[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"content-index":3,"content-layer:magnets:investigate":1434},{"release":4,"domains":9,"concepts":110,"edges":1322,"journeys":1431,"sources":1432,"glossary":1433,"lean":147},{"releaseId":5,"mode":6,"createdAt":7,"manifestHash":8},"remote-muarqumu","approved","2026-09-21T04:52:24.342Z","efdbdc0e58f4c54e74ab5330ffe7aa73dd8184fc4b473a83b828fd400c1b6143",[10,40,62,76,86,100],{"id":11,"title":12,"description":13,"order":14,"areas":15},"mathematics","Mathematics","Numbers, shapes, patterns and data — and the reasoning that connects them.",0,[16,20,24,28,32,36],{"id":17,"title":18,"description":19},"math-number","Numbers","Reading, writing and comparing large numbers, their properties, the four operations and the order we do them in.",{"id":21,"title":22,"description":23},"math-factors","Factors and multiples","Prime and composite numbers, twin primes and co-primes, HCF and LCM.",{"id":25,"title":26,"description":27},"math-patterns","Patterns","Finding the rule behind number and shape patterns, and using it to predict.",{"id":29,"title":30,"description":31},"math-geometry","Geometry","Shapes and solids, lines and rays, and the angles they make.",{"id":33,"title":34,"description":35},"math-measurement","Measurement","Measuring and constructing angles with a protractor, ruler and compass.",{"id":37,"title":38,"description":39},"math-data","Data handling","Collecting and organising data, and summarising it with mean, median, mode and range.",{"id":41,"title":42,"description":43,"order":44,"areas":45},"matter-energy","Physics","Light, sound, forces, energy and electricity — how the physical world behaves.",1,[46,50,54,58],{"id":47,"title":48,"description":49},"phys-light","Light","How light travels, what it does when it meets things, and why we see colour.",{"id":51,"title":52,"description":53},"phys-sound","Sound","Vibrations that travel through materials, and how we hear them.",{"id":55,"title":56,"description":57},"phys-forces","Forces and motion","Pushes, pulls and the force that holds moons, planets and falling apples.",{"id":59,"title":60,"description":61},"phys-electricity","Electricity and magnetism","Charge, circuits, power and magnets.",{"id":63,"title":64,"description":65,"order":66,"areas":67},"earth-space","Earth and space","Our planet, its oceans and skies, and the Sun and Moon that move them.",2,[68,72],{"id":69,"title":70,"description":71},"earth-space-astro","Sun, Moon and sky","What we see in the sky, why it changes, and what is really moving.",{"id":73,"title":74,"description":75},"earth-oceans","Oceans","Seas, coasts and the daily rise and fall of the tide.",{"id":77,"title":78,"description":79,"order":80,"areas":81},"living-world","Living world","Bodies, plants, animals and the systems that keep them alive.",3,[82],{"id":83,"title":84,"description":85},"bio-body","The human body","What is inside you, where it sits, and how the parts work together.",{"id":87,"title":88,"description":89,"order":90,"areas":91},"people-society","People and society","How people organise themselves, and what happens when they travel, trade and rule.",4,[92,96],{"id":93,"title":94,"description":95},"soc-government","Government and citizenship","Who makes the rules, who carries them out, and how people have a say.",{"id":97,"title":98,"description":99},"soc-exploration","Exploration and encounter","Why people set out into the unknown, and what followed for everyone involved.",{"id":101,"title":102,"description":103,"order":104,"areas":105},"technology","Technology","How tools, machines and computers are designed and used.",5,[106],{"id":107,"title":108,"description":109},"tech-engineering","Engineering and power","Designing machines, structures and energy systems.",[111,179,239,286,339,389,438,488,540,587,637,689,738,788,827,876,928,979,1029,1076,1125,1177,1227,1275],{"id":112,"slug":112,"title":113,"question":114,"promise":115,"domains":116,"areas":117,"keywords":118,"status":139,"layers":140,"questionBank":172},"human-body-anatomy","Anatomy of the human body","What is inside you, and where exactly does it all sit?","A guided tour of the body: bones that hold you up, muscles that move you, and the organs packed inside — what each one is, where it sits, and how big it really is.",[77],[83],[119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138],"anatomy","organ","skeleton","bone","muscle","heart","lungs","brain","stomach","liver","kidney","intestine","skin","joint","ribcage","spine","diaphragm","cell","tissue","body systems","available",[141,149,155,161,167],{"depth":142,"revision":44,"title":143,"subtitle":144,"summary":145,"estimatedMinutes":146,"reviewed":147,"reviewMethod":148},"discover","A guided tour of the body you live in","What is inside you, where it sits, and how big it really is","Climb the ladder from cells to organ systems, learn the words anatomists use for where things are, meet the 206 bones and their joints, find out why a muscle can only ever pull, and take an organ-by-organ tour with real sizes and positions — then measure your own body.",38,true,"owner_bulk",{"depth":150,"revision":44,"title":151,"subtitle":152,"summary":153,"estimatedMinutes":154,"reviewed":147,"reviewMethod":148},"understand","How the body is put together","Tissues, bone, joints, muscle and the cavities that hold the organs","Go one level below the organs to the four tissue types they are built from, learn the direction words and the standard pose they are measured from, see why bone is a living composite, count the skeleton to 206, and place every major organ in its cavity with its mass.",42,{"depth":156,"revision":44,"title":157,"subtitle":158,"summary":159,"estimatedMinutes":160,"reviewed":147,"reviewMethod":148},"investigate","Predict it, then test it","Seven claims about your body, tested with paper, a tape measure and real class data","Guess before you look: does a hollow tube beat a solid rod, does height equal arm span for everyone, can a bone reveal a stranger’s height, does exercise raise every pulse equally, are you really symmetric, and does your shoulder really out-move your hip? Seven hands-on tests against real evidence.",36,{"depth":162,"revision":44,"title":163,"subtitle":164,"summary":165,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"deepen","Why it works: levers, remodelling and a history of being corrected","Lever mechanics in every joint, bone that rebuilds under load, and how anatomy overturned a thousand years of error","Treat every muscle-moved bone as a lever and see why the body favours the class that trades force for speed. Meet bone that rebuilds along its real loads, the genuine edge cases in \"206 bones\", and how Vesalius corrected centuries of Galen’s animal-based errors.",40,{"depth":168,"revision":44,"title":169,"subtitle":170,"summary":171,"estimatedMinutes":146,"reviewed":147,"reviewMethod":148},"extend","Beyond the syllabus: animals, projects, puzzles and careers","Other body plans, three things to build, puzzles worth reasoning through, and where this knowledge earns a living","Compare your body plan with a giraffe, a bird, a snake and a boneless octopus; build a working paper hand and a life-size organ map; solve puzzles spanning the whole topic; meet seven careers built on this knowledge; finish with open questions.",{"count":173,"sections":174,"levels":175},79,10,{"foundation":176,"core":177,"stretch":178,"challenge":174},22,32,15,{"id":180,"slug":180,"title":181,"question":182,"promise":183,"domains":184,"areas":185,"keywords":186,"status":139,"layers":207,"questionBank":231},"angles","Angles","How much does a door turn when it opens — and how do we measure a turn?","What an angle is, types of angles, angle pairs (complementary, supplementary, linear pairs, vertically opposite) and how to use them to find missing angles.",[11],[29],[187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206],"angle","vertex","arm","degrees","acute","right angle","obtuse","straight angle","reflex","complete angle","complementary","supplementary","linear pair","vertically opposite","adjacent angles","angles at a point","clock angles","transversal","parallel lines","angle sum of a triangle",[208,213,218,222,227],{"depth":142,"revision":44,"title":209,"subtitle":210,"summary":211,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Angles are turns","Doors, clocks, scissors and compass directions: meet the angle and learn to name its size","See an angle as a turn and as two arms meeting at a vertex. Measure turns in degrees (full 360°, half 180°, quarter 90°), sort angles into seven types, turn through N, E, S, W, read angles on a clock and meet angle partners.",35,{"depth":150,"revision":44,"title":214,"subtitle":215,"summary":216,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Naming, sorting and pairing angles","Precise definitions, the seven types, and the angle pairs that let you find what you cannot measure","Define an angle as two rays with a common vertex, name it with ∠ABC, and use degrees and landmark angles. Pin down the seven types, clock and compass angles, then adjacent, complementary, supplementary, linear-pair, vertically opposite and around-a-point angles.",45,{"depth":156,"revision":44,"title":219,"subtitle":220,"summary":221,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Is it always true? Testing angle ideas","Predict, test with labs and numbers, hunt counterexamples and find the reasons behind angle patterns","Investigate angle estimation, sums of angle types, complement and supplement patterns, linear pairs and their bisectors, crossing lines, clock-hand puzzles, turning walks around shapes and the tear-the-corners experiment, sorting claims into always, sometimes and never.",{"depth":162,"revision":44,"title":223,"subtitle":224,"summary":225,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Why angles behave: proofs, parallels and polygons","From Babylonian 360 to Euclid's proofs: transversals, triangle and polygon angle sums, and hard missing-angle problems","Why a full turn is 360°, how to write a proof with reasons, why vertically opposite angles are equal, the angles made by a transversal on parallel lines and their converses, the triangle and polygon angle sums, bends and zigzags between parallels, and where 180° fails.",55,{"depth":168,"revision":44,"title":228,"subtitle":229,"summary":230,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Angles at work and play","Clock formulas, exterior angles, bearings, radians, real-world angles, olympiad puzzles and projects","Use |30h − 5.5m| for any clock time, prove and use the exterior angle property, navigate with bearings and runway numbers, meet the radian, see angles in ramps, ladders, bowling and pie charts, and tackle olympiad-style angle chases, projects and open questions.",{"count":232,"sections":233,"levels":234},80,9,{"foundation":235,"core":236,"stretch":237,"challenge":238},20,28,21,11,{"id":240,"slug":240,"title":241,"question":242,"promise":243,"domains":244,"areas":245,"keywords":246,"status":139,"layers":261,"questionBank":281},"body-systems","Body systems and how they connect","No organ works alone — so how does a mouthful of roti reach your toes as energy?","Digestive, circulatory, respiratory, nervous, muscular, skeletal and excretory systems, and the handovers between them that keep you alive every second.",[77],[83],[247,248,249,250,251,252,253,254,255,256,257,195,258,259,260],"digestive system","circulatory system","respiratory system","nervous system","excretory system","muscular system","skeletal system","blood","oxygen","nutrients","homeostasis","heart rate","breathing","interconnected",[262,266,270,273,277],{"depth":142,"revision":44,"title":263,"subtitle":264,"summary":265,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Seven teams, one body","What each system does, and where it hands the work to the next one","Meet the organ systems one at a time — digestive, respiratory, circulatory, excretory, nervous, muscular and skeletal — then follow a roti and a breath across the hand-over points where each system passes its work to the next.",{"depth":150,"revision":44,"title":267,"subtitle":268,"summary":269,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"How the systems work, and how they hand over","One design used six times: thin wall, huge surface, steep difference","Go inside each system: enzymes and the chemical works, the pressure trick that moves air, two circuits through a four-chambered heart, filter-and-reclaim kidneys, the reflex arc and the nerve-to-muscle gap — then follow a breath all the way to a working cell.",{"depth":156,"revision":44,"title":157,"subtitle":271,"summary":272,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Reaction time, a real enzyme test, exercise data and a fever that is not a malfunction","Turn the claims from earlier layers into experiments you can actually run: a ruler-drop reaction test, an iodine test for digested starch, pulse and breathing data before and after exercise, and a look at why a fever is a controlled response rather than a failure.",{"depth":162,"revision":44,"title":274,"subtitle":275,"summary":276,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Where the tidy rule bends","The mathematics of a thin wall, bone's double life, the lymphatic system, and why some hand-overs must be prevented","Quantify why hand-over barriers must be thin, meet the lymphatic system that returns leaked fluid and carries digested fat, see bone as a blood factory and calcium bank, and look at clotting and the blood-brain barrier as hand-overs the body deliberately controls or resists.",{"depth":168,"revision":44,"title":278,"subtitle":279,"summary":280,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"History, machines and weightlessness","Harvey's arithmetic, the stethoscope and ECG, three ways to image the body, artificial hand-overs, and bodies in orbit","Meet the arithmetic that proved blood circulates, the instruments that let doctors listen to and image a living body without cutting it, machines that rebuild a failed hand-over, what microgravity does to every system at once, and a few careers and open questions this topic leads to.",{"count":173,"sections":233,"levels":282},{"foundation":176,"core":283,"stretch":284,"challenge":285},25,19,13,{"id":287,"slug":287,"title":38,"question":288,"promise":289,"domains":290,"areas":291,"keywords":292,"status":139,"layers":313,"questionBank":335},"data-handling","What is a typical value — and how can one number summarise a whole class?","Collecting and organising data, tally marks and frequency tables, bar graphs, and summarising data with mean, median, mode and range.",[11],[37],[293,294,295,296,297,298,299,300,301,302,303,304,305,306,307,308,309,310,311,312],"data","mean","median","mode","range","average","tally","frequency table","bar graph","pictograph","pie chart","double bar graph","grouped data","outlier","survey","probability","census","rainfall","batting average","raw data",[314,318,322,326,330],{"depth":142,"revision":44,"title":315,"subtitle":316,"summary":317,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Counting what matters: meeting data","From a messy list of answers to one number that tells the story","Ask a question, collect answers, and turn a jumble of raw data into tally marks, tables, pictographs and bar graphs. Then meet four friendly numbers that sum up a whole group: the fair share (mean), the middle (median), the most common (mode) and the spread (range).",{"depth":150,"revision":44,"title":319,"subtitle":320,"summary":321,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Organise, picture, summarise: how the methods work","Kinds of data, tables and graphs done properly, and exact methods for mean, median, mode and range","Tell categorical from numerical data, build self-checking frequency tables, choose a key or scale for pictographs and bar graphs, and use exact methods for mean, median (odd and even counts), mode (two modes or none) and range, even from a frequency table.",{"depth":156,"revision":44,"title":323,"subtitle":324,"summary":325,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"What happens if…? Experiments with averages","Predict, change the data, and test: outliers, shifts, missing values and datasets built to order","Treat averages like a science experiment. Predict what adding a value, an outlier, or a change to every value does to the mean, median, mode and range, then test it in the labs. Build data sets to order, hunt missing values and compare real Indian data.",{"depth":162,"revision":44,"title":327,"subtitle":328,"summary":329,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Why averages work, and which one to trust","Balance points, proofs, grouped data, combined groups and the art of choosing an average","Prove the mean is a balance point and how it reacts to shifts and scaling. Combine groups correctly, handle grouped data with class intervals, read double bar graphs, and choose between mean, median and mode with outliers, cricket averages and average speeds. Plus a history of statistics in India.",{"depth":168,"revision":44,"title":331,"subtitle":332,"summary":333,"estimatedMinutes":334,"reviewed":147,"reviewMethod":148},"Data in the wild: pie charts, tricks, chance and projects","Draw pie charts, catch misleading graphs, talk about chance, and investigate real Indian data","Turn data into pie charts with angles, spot graphs that mislead, describe chance from impossible to certain, and run real projects on electricity bills, the census and monsoon rain. Think about privacy and fairness in data, meet careers built on data, and try olympiad-style puzzles.",60,{"count":232,"sections":233,"levels":336},{"foundation":337,"core":338,"stretch":176,"challenge":174},18,30,{"id":340,"slug":340,"title":341,"question":342,"promise":343,"domains":344,"areas":345,"keywords":346,"status":139,"layers":362,"questionBank":383},"eclipses","Eclipses","If the Moon goes round Earth every month, why isn't there an eclipse every month?","An eclipse is a shadow falling exactly where it can be seen. Learn the geometry of umbra and penumbra, why the Moon's tilted orbit makes eclipses rare, and how to watch one safely.",[63],[69],[347,348,349,350,351,352,353,354,355,356,357,358,359,360,361],"eclipse","solar eclipse","lunar eclipse","umbra","penumbra","annular","totality","syzygy","nodes","orbit tilt","Saros","corona","blood moon","eye safety","shadow",[363,367,371,375,379],{"depth":142,"revision":44,"title":364,"subtitle":365,"summary":366,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"An eclipse is a shadow that finds you","Two shadows, two kinds of eclipse, and how to watch one without hurting your eyes","Meet eclipses as what they really are: shadows. Learn whose shadow falls on what in solar and lunar eclipses, why the eclipsed Moon turns red, why we don't get one every month, and the safe ways to watch the Sun.",{"depth":150,"revision":44,"title":368,"subtitle":369,"summary":370,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"The geometry of a shadow in space","Umbra and penumbra, apparent sizes, nodes and seasons — and the reasons behind every safety rule","Work out the actual geometry: how long each shadow cone is, why the Moon's only just reaches us, why the discs match to 3%, how far from a node an eclipse can happen, why the Moon turns red, and the physics behind every solar viewing rule.",{"depth":156,"revision":44,"title":372,"subtitle":373,"summary":374,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Build it, test it, try to break it","A lamp-and-balls model, hands-on measurements, and predictions checked against real eclipses","Hands-on layer: build a scale model of the Earth-Moon-Sun system, test the new-moon\u002Ffull-moon rule and the shadow-width formula for yourself, find the tilt's hidden threshold, build a pinhole projector and check its numbers, and plan around three real upcoming eclipses.",{"depth":162,"revision":44,"title":376,"subtitle":377,"summary":378,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"The Saros cycle, and two eclipses that changed physics","The Saros arithmetic, the astronomers who computed it, and how a belief should really be tested","Deeper reasoning: rebuild the 1.474° eclipse limit term by term, derive the Saros and exeligmos cycles from three different lunar months, see how Aryabhata and Brahmagupta actually computed eclipses, and examine the two solar eclipses that discovered helium and tested general relativity.",{"depth":168,"revision":44,"title":380,"subtitle":381,"summary":382,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"The same shadow rule, everywhere in the Solar System","Moons too small to eclipse, a moon that eclipses constantly, transits at home, and other worlds' planets","Take the eclipse geometry beyond Earth: why Phobos and Deimos only ever transit the Sun from Mars, why Io causes true eclipses on Jupiter routinely, how Mercury and Venus transit the Sun from Earth, Venus's 243-year transit rhythm, and how the same trick finds other stars' planets.",{"count":384,"sections":385,"levels":386},68,8,{"foundation":235,"core":387,"stretch":388,"challenge":385},24,16,{"id":390,"slug":390,"title":391,"question":392,"promise":393,"domains":394,"areas":395,"keywords":396,"status":139,"layers":416,"questionBank":437},"electricity","Electricity","What actually happens between the power station and the switch under your finger?","Electricity is charge on the move. Learn what pushes it, what resists it, how it is made and delivered, what it costs, and how to stay safe around it.",[41,101],[59,107],[390,397,398,399,400,401,402,403,404,405,406,407,408,409,410,411,412,413,414,415],"voltage","current","resistance","Ohm's law","circuit","AC","DC","generator","power station","grid","transformer","kWh","electricity bill","safety","MCB","earth wire","battery","conductor","insulator",[417,421,425,429,433],{"depth":142,"revision":44,"title":418,"subtitle":419,"summary":420,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Electricity is charge on the move","From a balloon on your hair to a day that runs on it","Meet the charges hiding in every atom, see why a doorknob spark and lightning are the same idea, discover why slow electrons still light a bulb instantly, build circuits that break, and learn the first rules for staying safe.",{"depth":150,"revision":44,"title":422,"subtitle":423,"summary":424,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"The big three: voltage, current, resistance","The push, the flow and the pushback, and the one rule that ties them together","Build the pump-and-pipe picture of a circuit, then meet voltage (the push), current (the flow) and resistance (the pushback) with real numbers from AA cells to lightning. Finish with Ohm's law, V = I × R, and the mix-ups it clears up.",{"depth":156,"revision":44,"title":426,"subtitle":427,"summary":428,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Circuits you can test","Fair tests, meters, series and parallel, Ohm's law, fuses and fruit batteries","Design fair circuit tests, place ammeters and voltmeters correctly, compare series and parallel bulbs, test Ohm's law and see a filament bulb break it, work out when an MCB trips, and build a safe lemon battery.",{"depth":162,"revision":44,"title":430,"subtitle":431,"summary":432,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"How it's made and how it reaches you","From Faraday's spinning magnets to the socket on your wall","Follow electricity from a spinning magnet in a power station, through transformers and 765 kV lines, down to the 230 V socket in your room. Learn why the grid runs on AC at 50 Hz, why it transmits at high voltage, and why supply must match demand every second.",{"depth":168,"revision":44,"title":434,"subtitle":435,"summary":436,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Power, bills, safety and the future","From watts on a rating plate to units on your bill, the milliamps that matter, and the grid that is coming","Use P = V × I and E = P × t to read rating plates and work out a real electricity bill in units (kWh). Learn why current through the body is what injures, how earth pins, MCBs and RCCBs protect you, what to do in a shock emergency, and how solar, storage and smart meters are changing the grid.",null,{"id":439,"slug":439,"title":440,"question":441,"promise":442,"domains":443,"areas":444,"keywords":445,"status":139,"layers":463,"questionBank":485},"exploration","Exploration: reasons and consequences","What made people sail into oceans they could not map — and who paid for it?","Curiosity, trade, faith, gold and rivalry sent people across oceans. Follow the voyages, the technology that made them possible, and the consequences — for those who travelled and for those already there.",[87],[97],[439,446,447,448,449,450,451,452,453,454,455,456,457,458,459,460,461,462],"voyage","navigation","trade route","spices","Vasco da Gama","Columbus","Zheng He","Silk Road","colonisation","Columbian exchange","monsoon winds","astrolabe","compass","cartography","empire","consequences","indigenous peoples",[464,468,473,477,481],{"depth":142,"revision":44,"title":465,"subtitle":466,"summary":467,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Why sail into an ocean nobody has mapped?","Reasons, routes and results, told from both ends of the voyage","Meet exploration honestly: what the word means and why 'discovery' misleads, six reasons people set out, the busy Indian Ocean world before European ships, how sailors found their way, four voyages worth knowing, and what followed - new foods, new maps, disease, slavery and empire.",{"depth":150,"revision":44,"title":469,"subtitle":470,"summary":471,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"How the navigator's toolkit actually works","Mechanisms behind the voyages: instruments, sails, clocks, charts and the economics of a monopoly","Go under Discover's story to the mechanisms: how a compass, kamal, astrolabe, lateen sail and sternpost rudder actually work, why longitude needed a clock and took decades to solve, how flat maps must distort a round Earth, and why a royal charter let a trading company become a ruler.",50,{"depth":156,"revision":44,"title":474,"subtitle":475,"summary":476,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Predict it, try it, compare it, test it","Lab-heavy investigations that check what the Discover layer told you","Compare stated reasons with actual results for Columbus and Zheng He, run a monsoon 'what if', judge whether one number sums up a disputed history, sort evidence against a claim about da Gama, read a paraphrased passage from two sides, and test sweeping generalisations against real voyages.",{"depth":162,"revision":44,"title":478,"subtitle":479,"summary":480,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Mechanism, harder numbers, and how historians know","Why the monsoon reverses, how clock drift compounds, and the method behind contested figures","Go beneath Discover's facts into mechanism and method: why the monsoon reverses, how clock drift compounds over a long voyage, an edge case in kamal readings, how historians back-project contested figures, how to weigh one account against another, and what shipwreck years teach about mean vs median.",{"depth":168,"revision":44,"title":482,"subtitle":483,"summary":484,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Beyond the horizon: exploration to today","Cook, the poles, space, the deep sea, and the questions nobody has answered yet","Carries exploration from Cook's Pacific voyage to today: the race to the poles and the treaty that followed, leaving Earth's gravity for the Moon and beyond, the deepest ocean trench, and the hardest open questions - who owns what nobody lives on, and who decides.",{"count":486,"sections":233,"levels":487},75,{"foundation":178,"core":236,"stretch":176,"challenge":174},{"id":489,"slug":489,"title":490,"question":491,"promise":492,"domains":493,"areas":494,"keywords":495,"status":139,"layers":515,"questionBank":536},"four-operations","Four operations","When should you add, subtract, multiply or divide — and how do you know your answer makes sense?","Addition, subtraction, multiplication and division with large numbers, choosing the right operation in real problems, and checking answers by estimating and by inverse operations.",[11],[17],[496,497,498,499,500,501,502,503,504,505,506,507,508,509,510,511,512,513,514],"addition","subtraction","multiplication","division","word problems","estimation","inverse operations","quotient","remainder","dividend","divisor","product","sum","difference","regrouping","long division","long multiplication","unitary method","word problems in rupees",[516,520,524,528,532],{"depth":142,"revision":44,"title":517,"subtitle":518,"summary":519,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Four ways to change a number","Adding, subtracting, multiplying and dividing: what each one means and when to use it","Meet the four operations through a kirana-shop trip, cricket scores, egg trays and shared laddoos. Learn what each operation means, how they undo each other, how to pick the right one from a story, and how to check that an answer is sensible.",{"depth":150,"revision":44,"title":521,"subtitle":522,"summary":523,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"How the column methods work","Carrying, borrowing, long multiplication and long division, and why every step is allowed","Learn the exact name for every part of a calculation, then master column addition and subtraction up to crores, long multiplication, long division with remainders and zeros in the quotient, checking with inverse operations, and working with money and units.",{"depth":156,"revision":44,"title":525,"subtitle":526,"summary":527,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Predict, test, check","Estimating first, changing the numbers, making sense of remainders and catching keyword traps","Predict before you calculate and test with labs and tables: estimate sums and products, see what happens when numbers change, decide what a remainder means in a story, catch misleading keywords and check answers by undoing them.",{"depth":162,"revision":44,"title":529,"subtitle":530,"summary":531,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Why the methods work","Regrouping, the distributive property, the division algorithm, checks, proportion and the history behind them","Prove why carrying, borrowing, long multiplication and long division work, meet the division algorithm and why dividing by zero is impossible, check with casting out nines, use the unitary method wisely, and solve India-sized multi-step problems.",{"depth":168,"revision":44,"title":533,"subtitle":534,"summary":535,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Other ways to calculate, and harder puzzles","Lattices, Vedic-style shortcuts, doubling, binary, classic puzzles, olympiad problems and real projects","Try the lattice, Napier's bones, Vedic-style shortcuts and Russian peasant multiplication and see why each works. Crack classic puzzles and olympiad problems, then plan real projects: a trip budget, a kirana bill, a harvest and a run chase.",{"count":537,"sections":385,"levels":538},74,{"foundation":178,"core":539,"stretch":176,"challenge":385},29,{"id":541,"slug":541,"title":542,"question":543,"promise":544,"domains":545,"areas":546,"keywords":547,"status":139,"layers":563,"questionBank":584},"gravity","Gravity","Why does everything fall down — and what is the Moon falling towards?","The force that pulls an apple to the ground is the same one that keeps the Moon circling Earth. Meet mass and weight, free fall, orbits and why astronauts float.",[41],[55],[541,548,549,550,551,552,553,554,555,556,557,558,559,560,561,562],"mass","weight","free fall","orbit","force","Newton","air resistance","g","acceleration","satellite","weightlessness","planet","tides","escape velocity","centre of mass",[564,568,572,576,580],{"depth":142,"revision":44,"title":565,"subtitle":566,"summary":567,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Why does everything fall down?","Meet the pull that drops a pencil, bends the Moon’s path and holds the sky together","Start with a dropped pencil and end with galaxies. Discover what a force is, why heavy things do not fall faster, how air changes everything, the real difference between mass and weight, and the true reason astronauts float.",{"depth":150,"revision":44,"title":569,"subtitle":570,"summary":571,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"How gravity works: weight, falling and orbits","Mass against weight, g against speed, drag against gravity — and why an orbit is a permanent miss","Turn the story into rules you can use: weight = mass × g, distance = ½ g t², why mass cancels in free fall, how drag sets terminal velocity, Newton’s universal law in words, and the real reason astronauts float.",{"depth":156,"revision":44,"title":573,"subtitle":574,"summary":575,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Test it: predictions, ramps, pendulums and Newton’s own proof","Predict, try, compare and ask \"is it always true?\" — with a ramp, a pendulum, a leaking cup and a spacecraft","Turn gravity into hands-on science: rebuild Galileo’s ramp, design fair tests for mass and shape, weigh the Earth with a pendulum, check whether Newton’s law survives the trip to the Moon, hunt for orbital speed by binary search, and see how ISRO climbs to the Moon and Mars one burn at a time.",{"depth":162,"revision":44,"title":577,"subtitle":578,"summary":579,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"The mathematics behind every number in this topic","G, orbits derived from first principles, Newton’s Moon test in full, and the coincidence Einstein could not ignore","Meet Newton’s law with its constant G, derive orbital and escape speed from scratch, redo Newton’s Moon test in full, explore why gravitational and inertial mass are equal, see why g is not uniform on Earth, and look at the mechanics behind ISRO’s orbit-raising missions.",{"depth":168,"revision":44,"title":581,"subtitle":582,"summary":583,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Curved spacetime, black holes and the questions nobody has answered yet","Einstein’s radical idea, tested and confirmed — and an honest look at where gravity’s biggest mysteries still are","Go beyond Newton to Einstein: gravity as curved spacetime, the rubber-sheet picture and its flaws, the tests that confirmed general relativity, black holes, gravitational waves, orbital puzzles from tidal locking to dark matter, and open questions with real projects.",{"count":585,"sections":233,"levels":586},70,{"foundation":388,"core":387,"stretch":235,"challenge":174},{"id":588,"slug":588,"title":589,"question":590,"promise":591,"domains":592,"areas":593,"keywords":594,"status":139,"layers":613,"questionBank":634},"hcf-and-lcm","HCF and LCM","When will two blinking lights flash together again — and what is the biggest tile that fits a floor exactly?","Highest common factor and lowest common multiple by listing, prime factorisation and division, their link HCF × LCM = product, and real problems that need them.",[11],[21],[595,596,597,598,599,600,601,602,603,604,605,606,607,608,609,610,500,611,612],"HCF","LCM","GCD","GCF","highest common factor","lowest common multiple","least common multiple","common factors","common multiples","prime factorisation","Venn diagram","long division method","Euclid's algorithm","common division method","co-prime","HCF × LCM","remainder problems","fractions",[614,618,622,626,630],{"depth":142,"revision":44,"title":615,"subtitle":616,"summary":617,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Sharing and meeting: meet the HCF and LCM","The biggest equal pieces and the next time things line up","Start from two puzzles, the biggest tile for a courtyard and the next time two lights flash together, and discover factors, multiples, common factors, common multiples, the HCF and the LCM, and how to tell which one a problem needs.",{"depth":150,"revision":44,"title":619,"subtitle":620,"summary":621,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Four ways to find the HCF and LCM","Listing, prime factors, long division and the ladder, and why they work","Precise definitions, then four methods: listing, prime factorisation with a Venn picture, long (continued) division for the HCF and common division for the LCM. Three numbers, the rule HCF × LCM = product, co-primes, fractions and the classic mix-ups.",{"depth":156,"revision":44,"title":623,"subtitle":624,"summary":625,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Predict, test and explain: HCF and LCM patterns","Always, sometimes or never? Find out with your own experiments","Make predictions and test them: when the LCM equals the product, why neighbours are co-prime, how HCF × LCM = a × b holds for two numbers but not three, what scaling does, how remainder puzzles work, and how changing a word problem changes the answer.",{"depth":162,"revision":44,"title":627,"subtitle":628,"summary":629,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Why it works: proofs, Euclid and the edges","Unique prime recipes, the product rule, Euclid’s algorithm and Bézout","Proofs in plain language: unique prime factorisation, why HCF takes smallest powers and LCM largest, why HCF × LCM = a × b (and why not for three numbers), why Euclid’s method works and how fast it is, Bézout’s identity, edge cases, harder problems and history.",{"depth":168,"revision":44,"title":631,"subtitle":632,"summary":633,"estimatedMinutes":334,"reviewed":147,"reviewMethod":148},"Cycles, gears and puzzles: HCF and LCM in the wild","Calendars, cicadas, tabla, bicycles, jugs, screens and olympiad problems","Expeditions beyond the textbook: cycles with head starts, calendars and planetary alignments (and why they are not LCMs), prime-cycle cicadas, gears and bicycle chains, tala rhythms, water jugs, ancient remainder puzzles, screen ratios, fractions, olympiad problems, careers and open questions.",{"count":173,"sections":385,"levels":635},{"foundation":235,"core":636,"stretch":337,"challenge":174},31,{"id":638,"slug":638,"title":639,"question":640,"promise":641,"domains":642,"areas":643,"keywords":644,"status":139,"layers":665,"questionBank":686},"government-india","How government works in India","Who decides what a country does — and where does a citizen fit in?","Parliament, the President and the Prime Minister, states and panchayats, courts and elections: how India makes its laws, carries them out and settles disputes, and how people have a say.",[87],[93],[645,646,647,648,649,650,651,652,653,654,655,656,657,658,659,660,661,662,663,664],"government","democracy","Parliament","Lok Sabha","Rajya Sabha","President","Prime Minister","Supreme Court","election","vote","constitution","panchayat","municipality","state","federal","law","rights","duties","citizen","judiciary",[666,670,674,678,682],{"depth":142,"revision":44,"title":667,"subtitle":668,"summary":669,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Who decides the rules?","From an hour in the school hall to a republic of a hundred and forty crore people","Start with thirty children, one football and no rules, and discover the three jobs every group has to invent: making rules, carrying them out and settling disputes. Then meet India's version — the Constitution, three organs, three levels, and the vote.",{"depth":150,"revision":44,"title":671,"subtitle":672,"summary":673,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"How each part actually works","Parliament's machinery, a bill's journey, the courts' ladder, and the levels beneath the Union","Go inside the institutions Discover introduced: how Parliament questions ministers, how a bill becomes an Act, what a President does that a Prime Minister does not, how courts check Parliament, and how the Union, States, Union Territories and local bodies share the work.",{"depth":156,"revision":44,"title":675,"subtitle":676,"summary":677,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Test it yourself: does the arithmetic hold up?","Seat share against vote share, real turnout data, and edge cases in how a bill becomes an Act","Put the rules from Understand under pressure: work through seat-versus-vote-share examples, test what happens when the two Houses disagree over a money bill, analyse real turnout data with mean, median and range, and sort everyday problems by the level of government actually responsible.",{"depth":162,"revision":44,"title":679,"subtitle":680,"summary":681,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Why it is built this way","The amendment procedure's arithmetic, the basic structure doctrine, and the freedom movement's fingerprints","Go after the reasoning: the arithmetic of amending the Constitution, the basic structure doctrine, how judges come to be chosen, the freedom movement's own arguments becoming institutions, and a few genuine edge cases put under pressure.",{"depth":168,"revision":44,"title":683,"subtitle":684,"summary":685,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Build it, test it, take it further","A mini-constitution, a mock Parliament, coalition puzzles, other countries' choices, and where this knowledge leads","Put the whole topic to work: draft and stress-test a mini-constitution, run a mock Parliament, prove a coalition-counting puzzle, compare India's design with other countries', research your own representatives, and meet real careers and open questions this knowledge connects to.",{"count":687,"sections":385,"levels":688},76,{"foundation":176,"core":636,"stretch":178,"challenge":385},{"id":690,"slug":690,"title":48,"question":691,"promise":692,"domains":693,"areas":694,"keywords":695,"status":139,"layers":713,"questionBank":735},"light","What is light, how does it travel, and why can you see this page at all?","Light travels in straight lines at extraordinary speed, bounces, bends, splits into colours and lets you see. Find out how, and why shadows, mirrors and rainbows behave as they do.",[41],[47],[690,696,697,698,361,699,700,701,702,703,704,705,706,707,708,709,710,350,711,712],"luminous","reflection","refraction","mirror","spectrum","colour","transparent","opaque","translucent","ray","speed of light","rainbow","prism","lens","eye","scattering","laser",[714,718,722,726,730],{"depth":142,"revision":44,"title":715,"subtitle":716,"summary":717,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Light: how you can see anything at all","Sources, straight lines, shadows, mirrors, bent straws and the colours hiding inside white","Meet light as the messenger that carries the world to your eyes: what makes its own light and what only reflects it, why light travels dead straight, how that one fact explains shadows, and first looks at mirrors, bending and the colours inside white light.",{"depth":150,"revision":44,"title":719,"subtitle":720,"summary":721,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"How light behaves: rays, angles and rules you can use","Shadow arithmetic, the law of reflection, what refraction really is, and the two kinds of colour mixing","Turn the facts of Discover into rules that predict. Work out shadow sizes with similar triangles, meet umbra and penumbra, apply the law of reflection to mirrors and periscopes, see why light bends when its speed changes, and separate the two opposite kinds of colour mixing.",{"depth":156,"revision":44,"title":723,"subtitle":724,"summary":725,"estimatedMinutes":154,"reviewed":147,"reviewMethod":148},"Chasing light: measuring, mirroring and bending it on purpose","How fast is light, and how would you find out? Predict and test curved mirrors, lenses, TIR and rainbows.","Step into the shoes of Rømer and Fizeau to measure something that seemed instant, then turn detective on curved mirrors, lenses pushed to a magnifier, total internal reflection in a diamond and a fibre-optic cable, and finally the exact geometry that puts a rainbow at 42 degrees from the Sun.",{"depth":162,"revision":44,"title":727,"subtitle":728,"summary":729,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Precise light: derivations, corrective lenses and the shape of a rainbow","Beyond the syllabus: derive the mirror formula, correct short and long sight, and see why a rainbow sits at 42 degrees.","Follow the speed of light to its modern exact definition, derive the mirror\u002Flens formula from similar triangles, work out lens powers for short and long sight, put numbers on fibre-optic latency, and see why the rainbow's angle is a genuine minimum.",{"depth":168,"revision":44,"title":731,"subtitle":732,"summary":733,"estimatedMinutes":734,"reviewed":147,"reviewMethod":148},"Waves, particles and the light you cannot see","Beyond visible light: wave versus particle, a real chocolate-bar experiment, and looking into the past with light-years.","Step past visible light into the wider spectrum, meet the wave-versus-particle debate (light is genuinely both), measure light's speed with a microwave and a chocolate bar, see how bending stretches every day, and use light-years to look into the past.",44,{"count":232,"sections":233,"levels":736},{"foundation":284,"core":737,"stretch":284,"challenge":178},27,{"id":739,"slug":739,"title":740,"question":741,"promise":742,"domains":743,"areas":744,"keywords":745,"status":139,"layers":763,"questionBank":784},"lines","Lines, rays and line segments","What is the difference between a line, a ray and a segment — and why do railway tracks never meet?","Points, lines, rays and line segments, intersecting, parallel and perpendicular lines, and where we see them in the world.",[11],[29],[746,747,705,748,749,750,751,752,205,753,754,204,755,756,757,758,759,760,761,762],"point","line","line segment","plane","collinear","concurrent","intersecting lines","perpendicular lines","perpendicular bisector","skew lines","horizontal and vertical","measuring segments","parallax error","Euclid's postulates","parallel postulate","vanishing point","railway tracks",[764,768,772,776,780],{"depth":142,"revision":44,"title":765,"subtitle":766,"summary":767,"estimatedMinutes":283,"reviewed":147,"reviewMethod":148},"Straight paths: points, lines, rays and segments","Meet the alphabet of geometry in torch beams, railway tracks and cricket creases","Meet points, line segments, rays and lines through everyday things, then see how two lines can cross, meet at square corners or run side by side forever.",{"depth":150,"revision":44,"title":769,"subtitle":770,"summary":771,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Names, notation and rules for lines","Precise definitions, careful measuring and the mix-ups they clear up","Pin down point, line and plane; name lines, rays and segments correctly; measure without parallax error; and define collinear, concurrent, parallel and perpendicular lines precisely.",{"depth":156,"revision":44,"title":773,"subtitle":774,"summary":775,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Test it: predictions about points and lines","Count, fold, measure and hunt for counterexamples","Predict and count how many lines, segments, rays and crossing points some points and lines can make; run a measuring experiment; beat optical illusions; and sort claims into always, sometimes and never true.",{"depth":162,"revision":44,"title":777,"subtitle":778,"summary":779,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Why it must be so: reasoning about lines","Euclid's rules, proofs, counting arguments and the puzzle of parallels","Build geometry from Euclid's postulates, prove key facts about intersecting, parallel and perpendicular lines, count with pairs, and follow the 2,000-year story of the parallel postulate from Alexandria to curved space.",{"depth":168,"revision":44,"title":781,"subtitle":782,"summary":783,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Lines in the wider world","Perspective, skew lines, maps, sport, careers, puzzles and open questions","See parallel lines meet in perspective drawings, find skew lines in rooms and solids, read lines on maps and sports grounds, meet people who use lines at work, and tackle puzzles from pizza cuts to string art.",{"count":232,"sections":233,"levels":785},{"foundation":786,"core":539,"stretch":176,"challenge":787},17,12,{"id":789,"slug":789,"title":790,"question":790,"promise":791,"domains":792,"areas":793,"keywords":794,"status":139,"layers":800,"questionBank":823},"magnets","Magnets: why do some things stick to a magnet and others do not?","A new science topic for learners aged 10 to 12 (Class 5-6, India). Cover: what a magnet is; poles, attraction and repulsion; which materials are magnetic (iron, nickel, cobalt, steel) and which are not (wood, plastic, copper, aluminium); th",[41],[59],[789,795,796,797,798,799],"some","things","stick","magnet","others",[801,807,811,815,819],{"depth":142,"revision":44,"title":802,"subtitle":803,"summary":804,"estimatedMinutes":805,"reviewed":147,"reviewMethod":806},"The Invisible Grip: How Magnets Pull and Push","A journey from fridge magnets to Earth's hidden force — why some things stick and others slip away","This lesson introduces magnets through everyday objects, explains how poles attract and repel, and shows how to test materials for magnetism. Readers will map invisible magnetic fields, make a simple compass, and connect it all to Earth acting as a giant magnet.",90,"per_lesson",{"depth":150,"revision":44,"title":808,"subtitle":809,"summary":810,"estimatedMinutes":805,"reviewed":147,"reviewMethod":806},"The Hidden Army Inside a Magnet","How tiny atomic teams line up to pull, stick or snap — and why heat or a hard knock sends them tumbling","This lesson reveals the invisible world of magnetic domains: why iron sticks but copper slips, how stroking or electricity organises atoms into a magnet, and why heat or hammering destroys that order. It also covers common mix-ups like 'all metals attract' and how to test unknown",{"depth":156,"revision":44,"title":812,"subtitle":813,"summary":814,"estimatedMinutes":805,"reviewed":147,"reviewMethod":806},"The Magnet Investigation Lab","How changing conditions, careful measurement and fair tests reveal what magnets really do","This lesson puts every magnet claim to the test. Learners plan fair comparisons, predict outcomes, gather evidence and use it to decide how magnets behave, how they weaken, and how an electromagnet's design changes its power.",{"depth":162,"revision":44,"title":816,"subtitle":817,"summary":818,"estimatedMinutes":805,"reviewed":147,"reviewMethod":806},"The Invisible Architecture of Magnetism","How atoms, domains, and field lines explain why some materials obey the magnet and others refuse","This lesson traces magnetism from everyday fridge magnets to atomic arrangements and magnetic domains, explaining why iron rushes to a magnet while copper stays still. Readers learn to predict magnetic behaviour, interpret field-line patterns, and calculate simple field relations",{"depth":168,"revision":44,"title":820,"subtitle":821,"summary":822,"estimatedMinutes":805,"reviewed":147,"reviewMethod":806},"The Invisible Push: Magnets at Work and at Scale","From iron filings to maglev trains — how hidden fields, domains and electromagnets shape our world","This lesson explores how magnetic domains explain why some materials become magnets and others do not, then builds to electromagnets, real engineering uses, and how to test magnetism fairly at home. It closes with open questions about magnetic storage and levitation that learners",{"count":824,"sections":66,"levels":825},52,{"foundation":826,"core":337,"stretch":787,"challenge":385},14,{"id":828,"slug":828,"title":829,"question":830,"promise":831,"domains":832,"areas":833,"keywords":834,"status":139,"layers":853,"questionBank":874},"constructing-angles","Measuring and constructing angles","How do you draw an exact 60° angle with only a compass and a ruler?","Reading a protractor correctly, measuring and drawing angles, and constructing 60°, 120°, 90°, 30° and 45° angles and bisectors with a ruler and compass.",[11],[33,29],[835,458,836,837,754,838,839,840,841,842,843,844,845,846,847,848,849,850,851,852],"protractor","construction","angle bisector","60 degrees","90 degrees","120 degrees","45 degrees","30 degrees","geometry box","set square","divider","measuring angles","drawing angles","reflex angle","inner and outer scale","ruler and compass","trisection","constructing triangles",[854,858,862,866,870],{"depth":142,"revision":44,"title":855,"subtitle":856,"summary":857,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Angles you can measure and make","The geometry box, the protractor and the compass trick for an exact 60°","Open the geometry box, learn what a degree is, estimate angles by eye, measure and draw angles with a protractor, and discover how a compass alone can make an exact 60° angle.",{"depth":150,"revision":44,"title":859,"subtitle":860,"summary":861,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Reading the protractor and the compass constructions","Why the two scales exist, how to measure and draw any angle, and why 60°, 90°, 30° and 45° constructions work","Learn the precise protractor method (and the wrong-scale trap), measure and draw reflex angles, copy lengths with a compass, and construct 60°, 120°, 90°, 30° and 45° angles and perpendicular bisectors with the reason each one works.",{"depth":156,"revision":44,"title":863,"subtitle":864,"summary":865,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Test it: estimates, radii and angle recipes","Predict, try and check: what really changes an angle, and what never does","Predict and test: does arm length matter, what does a wrong-scale reading look like, how good is your eye, does the compass radius matter, which angles can bisecting and set squares reach, how accurate can a check be, and why bisectors always work.",{"depth":162,"revision":44,"title":867,"subtitle":868,"summary":869,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Why the constructions work","Proofs behind the recipes, edge cases, accuracy and the problems the Greeks could not solve","Find out why each compass construction is exact: equilateral triangles for 60°, congruent triangles for bisectors, equidistant points for perpendiculars. Then test edge cases, measure reflex angles, analyse errors and meet the impossible trisection problem.",{"depth":168,"revision":44,"title":871,"subtitle":872,"summary":873,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Triangles, polygons and the impossible angle","Build triangles and regular polygons, meet Gauss's 17-gon, and find out why 20° can never be constructed","Construct triangles from SSS, SAS and ASA, draw regular polygons from a circle, discover which polygons and whole-degree angles are constructible (multiples of 3°), meet the trisection problem, and use angles in projects, puzzles and careers.",{"count":537,"sections":233,"levels":875},{"foundation":178,"core":338,"stretch":284,"challenge":174},{"id":877,"slug":877,"title":878,"question":879,"promise":880,"domains":881,"areas":882,"keywords":883,"status":139,"layers":903,"questionBank":924},"patterns","Number and shape patterns","How can you predict the 100th term without drawing 100 pictures?","Spotting rules in number sequences and growing shape patterns, describing them in words and symbols, and using the rule to predict.",[11],[25],[877,884,885,886,887,888,889,890,891,892,893,894,895,896,897,898,899,900,901,902],"sequence","rule","term","nth term","repeating patterns","growing patterns","arithmetic sequence","geometric sequence","square numbers","cube numbers","triangular numbers","Fibonacci","Pascal's triangle","matchstick patterns","odd numbers","even numbers","magic squares","kolam","algebra",[904,908,912,916,920],{"depth":142,"revision":44,"title":905,"subtitle":906,"summary":907,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"What comes next? Meeting patterns","Bangles, kolam borders, calendars, matchsticks and the rules that make them","Meet repeating and growing patterns in beads, rangoli, calendars and the hundred square. Find the unit, find the difference, describe the rule in words, and use jumps to predict terms far ahead.",{"depth":150,"revision":44,"title":909,"subtitle":910,"summary":911,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Rules, terms and sequences","Arithmetic and geometric sequences, special numbers, digit patterns and shape rules","Learn the precise language of sequences, the difference method for finding rules, arithmetic and geometric sequences, square, cube, triangular and Fibonacci numbers, digit patterns, and the rules behind growing matchstick and dot patterns.",{"depth":156,"revision":44,"title":913,"subtitle":914,"summary":915,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Pattern detectives: predict, test, explain","Matchstick challenges, Gauss’s trick, calendar magic, growth races and patterns that fool you","Investigate growing patterns like a detective: predict first, collect small cases, find the rule, test it and explain why it works. Includes far predictions, working backwards, odd sums, Gauss’s pairing, grid tricks and always-sometimes-never reasoning.",{"depth":162,"revision":44,"title":917,"subtitle":918,"summary":919,"estimatedMinutes":334,"reviewed":147,"reviewMethod":148},"Why patterns work: rules, algebra and proof","nth terms, equivalent expressions, picture proofs, Pingala’s rhythms, Meru Prastara and patterns that break","Turn rules into algebra and prove them: why the step becomes the coefficient of n, why odd numbers make squares, sums of powers and cubes, the Indian discovery of the Fibonacci numbers and Meru Prastara, why digit patterns stop, and why patterns that look certain can break.",{"depth":168,"revision":44,"title":921,"subtitle":922,"summary":923,"estimatedMinutes":334,"reviewed":147,"reviewMethod":148},"Pattern hunters: puzzles, projects and open questions","Magic squares from Khajuraho, tessellations, figurate numbers, cycles, olympiad problems and unsolved mysteries","Take patterns into the wider world: Lo Shu, Khajuraho and Ramanujan magic squares, tessellations and symmetry, figurate numbers, cycles of last digits and weekdays, the chessboard legend and binary, olympiad problems, patterns in music and careers, projects, and open questions like Collatz.",{"count":925,"sections":233,"levels":926},81,{"foundation":178,"core":927,"stretch":387,"challenge":233},33,{"id":929,"slug":929,"title":930,"question":931,"promise":932,"domains":933,"areas":934,"keywords":935,"status":139,"layers":955,"questionBank":976},"number-system","Number system","How do we read, write and compare really big numbers — and why do Indians and the rest of the world put commas in different places?","Place value, number names, expanded form, predecessors and successors, the Indian and International systems, and rounding — the toolkit for every large number you will ever meet.",[11],[17],[936,937,938,939,940,941,942,943,944,945,946,947,501,948,949,950,951,952,953,954],"place value","number names","expanded form","predecessor","successor","Indian number system","International number system","lakh","crore","million","billion","rounding","comparing numbers","face value","Roman numerals","arab and kharab","Hindu-Arabic numerals","binary","expanded form with powers of ten",[956,960,964,968,972],{"depth":142,"revision":44,"title":957,"subtitle":958,"summary":959,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Big numbers all around us","Ten digits, a few clever places, and every number you will ever need","Meet place value through bundles of sticks, cricket crowds and rupee notes. Learn to read and write big numbers the Indian way (lakh, crore) and the international way (million, billion), find the number just before and after, compare, round and even read Roman numerals.",{"depth":150,"revision":44,"title":961,"subtitle":962,"summary":963,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"How place value works, and how to use it","Precise rules for names, commas, comparing, forming, rounding and estimating","Exact rules for place and face value, expanded form, number names and both comma systems, with many worked examples. Then reliable methods for converting, comparing, ordering, forming numbers, rounding, estimating and Roman numerals, plus the mix-ups to avoid.",{"depth":156,"revision":44,"title":965,"subtitle":966,"summary":967,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Testing big-number ideas","Predict first, then try it: shifting digits, rollovers, rounding traps and estimation errors","Make predictions about place value and then test them: what moving a digit does, how many numbers of each size exist, when a successor gains a digit, which numbers round to the same value, how far off an estimate can be, and why 6174 keeps appearing.",{"depth":162,"revision":44,"title":969,"subtitle":970,"summary":971,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Why place value works","Powers of ten, proofs of the rules, error bounds and the Indian story of zero","Powers of ten, and proofs that the rules for comparing, rounding and forming numbers always work. Bound estimate errors, meet Sanskrit names for powers of ten, follow our digits from Brahmi to Aryabhata to Baghdad to Europe, and see metric units as place value.",{"depth":168,"revision":44,"title":973,"subtitle":974,"summary":975,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Beyond a billion, and beyond base ten","Arab, kharab and trillion; ISRO distances; binary and other bases; puzzles and projects","Stretch the number system in every direction: bigger names in both systems, real Indian large numbers from elections to Mars, number systems of the Babylonians, Maya and Egyptians, binary as a place-value system, olympiad-style puzzles, Fermi estimates, projects and open questions.",{"count":977,"sections":233,"levels":978},83,{"foundation":235,"core":338,"stretch":176,"challenge":238},{"id":980,"slug":980,"title":981,"question":982,"promise":983,"domains":984,"areas":985,"keywords":986,"status":139,"layers":1006,"questionBank":1027},"order-of-operations","Order of operations","Is 2 + 3 × 4 equal to 20 or 14 — and who decides?","Why we need an agreed order, the DMAS \u002F BODMAS rule, brackets, and how the distributive property explains it all.",[11],[17],[987,988,989,990,991,992,993,994,995,996,997,998,999,1000,1001,1002,500,1003,1004,1005],"DMAS","BODMAS","BIDMAS","PEMDAS","order of operations","brackets","simplify","expression","terms","left to right","precedence","vinculum","of","implied multiplication","four fours","24 game","calculator","distributive property","nested brackets",[1007,1011,1015,1019,1023],{"depth":142,"revision":44,"title":1008,"subtitle":1009,"summary":1010,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"One line of maths, one answer","Why 2 + 3 × 4 is 14 everywhere in the world, and the simple rules that make it so","Meet the puzzle 2 + 3 × 4 through a shopping bill, learn why everyone needs one agreed order, and practise the three rules: brackets first, then × and ÷, then + and −, with partners going left to right.",{"depth":150,"revision":44,"title":1012,"subtitle":1013,"summary":1014,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"The rule, precisely","Terms, memory words, three kinds of brackets, “of”, word problems and error-spotting","Make the order of operations precise: split expressions into terms, see why DMAS, BODMAS and PEMDAS all mean one rule, handle nested brackets and \"of\", write expressions from word problems and find mistakes in working.",{"depth":156,"revision":44,"title":1016,"subtitle":1017,"summary":1018,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Brackets under the microscope","Predict, test and explain: moving brackets, missing signs, calculators and targets","Experiment with the order of operations: count how many values brackets can make, find when brackets change nothing, test always\u002Fsometimes\u002Fnever statements, fill in missing signs, compare calculators and hit targets.",{"depth":162,"revision":44,"title":1020,"subtitle":1021,"summary":1022,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Why the rule is the rule","Repeated addition, the distributive property, powers, the vinculum, history and how machines read maths","Justify the order of operations: why × comes before + (repeated addition, the distributive property), why partners go left to right (negatives and reciprocals), where powers fit, the vinculum and history of brackets, expression trees, RPN and edge cases.",{"depth":168,"revision":44,"title":1024,"subtitle":1025,"summary":1026,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Puzzles, arguments and the wider world","Viral puzzles, four fours, the 24 game, olympiad problems, code and open questions","Take the order of operations further: why 8 ÷ 2(2 + 2) starts arguments, the four fours and 24 puzzles, olympiad problems, how code and spreadsheets differ, other notations, projects and open questions.",{"count":486,"sections":385,"levels":1028},{"foundation":284,"core":636,"stretch":786,"challenge":385},{"id":1030,"slug":1030,"title":1031,"question":1032,"promise":1033,"domains":1034,"areas":1035,"keywords":1036,"status":139,"layers":1053,"questionBank":1074},"phases-of-the-moon","Phases of the Moon","Why does the Moon change shape — and why is it never really a different shape at all?","Half the Moon is always lit. What changes is how much of the lit half faces us. Follow the monthly cycle, learn the names, and find out why the Moon is up in the daytime too.",[63],[69],[1037,1038,1039,1040,1041,1042,1043,1044,1045,1046,551,1047,1048,1049,1050,1051,1052],"moon","phases","new moon","full moon","crescent","gibbous","waxing","waning","lunar month","synodic","tithi","Purnima","Amavasya","terminator","earthshine","far side",[1054,1058,1062,1066,1070],{"depth":142,"revision":44,"title":1055,"subtitle":1056,"summary":1057,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"The shape that changes — except it never does","Why the Moon looks different every night, and what is really going on","Meet the Moon's monthly cycle: borrowed sunlight, a ball that is always half lit, and eight named phases. Learn to tell waxing from waning tonight, find out why the Moon is up in the daytime, and kill the biggest myth in astronomy — that the phases are Earth's shadow.",{"depth":150,"revision":44,"title":1059,"subtitle":1060,"summary":1061,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Reading the Moon: one angle explains everything","Elongation, lit fraction, rise times, the terminator and why one face always faces us","Turn the phase picture into a tool. Learn to go from the Sun-Earth-Moon angle to the shape, the fraction lit and the rise and set times; find out why craters show best at quarter moon, what earthshine is, and why the Moon keeps one face towards Earth.",{"depth":156,"revision":44,"title":1063,"subtitle":1064,"summary":1065,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Put the Moon on trial","Eight investigations, from an orange and a lamp to a month-long diary","Stop reading and start checking. Build a working model of the phases with a ball and a lamp, keep a month-long moon diary, measure the fifty-minute daily lag against your own rooftop, hunt earthshine, and predict a festival moonrise well enough to announce it.",{"depth":162,"revision":44,"title":1067,"subtitle":1068,"summary":1069,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"The chase, the wobble and the brake","Deriving 29.53 days, the elastic tithi, adhik maas, eclipse rarity and the recession, from first principles","Go past the rules to the reasoning: derive the synodic month from two orbital speeds, see why a tithi stretches and shrinks, work out how often adhik maas is needed, derive eclipse rarity from the 5.1-degree tilt, and follow the torque that locked the Moon and is now pushing it away.",{"depth":168,"revision":44,"title":1071,"subtitle":1072,"summary":1073,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"To the wobble, the far side and the far future","Libration, Chandrayaan-3 and the south pole, deep time, other calendars, puzzles and open questions","Push past the settled parts of the topic: measure libration for yourself, trace the far side from Luna 3 to Chandrayaan-3, work out why total eclipses have an expiry date, compare world calendars, and take on puzzles and open questions nobody has fully answered.",{"count":486,"sections":233,"levels":1075},{"foundation":284,"core":387,"stretch":337,"challenge":826},{"id":1077,"slug":1077,"title":1078,"question":1079,"promise":1080,"domains":1081,"areas":1082,"keywords":1083,"status":139,"layers":1102,"questionBank":1123},"prime-and-composite","Prime and composite numbers","Why are some numbers impossible to split into equal groups?","Factors and multiples, prime and composite numbers, the Sieve of Eratosthenes, divisibility tests, twin primes and co-primes.",[11],[21],[1084,1085,1086,1087,1088,609,1089,1090,604,1091,1092,1093,1094,1095,1096,1097,1098,1099,1100,1101],"prime number","composite number","factor","multiple","twin primes","sieve of Eratosthenes","divisibility rules","factor tree","1 is neither","relatively prime","prime triplet","trial division","fundamental theorem of arithmetic","Euclid","Goldbach conjecture","Mersenne prime","perfect number","periodical cicadas",[1103,1107,1111,1115,1119],{"depth":142,"revision":44,"title":1104,"subtitle":1105,"summary":1106,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Numbers that will not make rectangles","Factors, multiples and the numbers that can only stand in a single line","Share laddoos, set out chairs and build rectangles from tiles to meet factors and multiples. Discover prime numbers, composite numbers, the odd case of 1, the Sieve of Eratosthenes, twin primes and co-primes.",{"depth":150,"revision":44,"title":1108,"subtitle":1109,"summary":1110,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Factors, primes and how to test them","Precise definitions, reliable methods and the mix-ups to avoid","Find every factor with the factor-pair method, sieve to 100 and see why you can stop at 7, test any number for primality by trial division up to its square root, use divisibility rules, and meet twin primes, co-primes and factor trees.",{"depth":156,"revision":44,"title":1112,"subtitle":1113,"summary":1114,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Hunting patterns among the primes","Predict, test and decide: which prime patterns are real, and which ones fool you?","Test claims about primes like a mathematician: how fast primes thin out, the 6-column grid, last digits, twin prime hunts, why 3, 5, 7 stands alone, co-prime experiments, patterns that break, prime deserts and numbers with the most factors.",{"depth":162,"revision":44,"title":1116,"subtitle":1117,"summary":1118,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Why it all works: proofs about primes","Unique factorisation, the square-root rule, the reasons behind divisibility tests, and Euclid’s endless primes","Prove that every number is built from primes in exactly one way, see a world where that fails, count factors from a factorisation, explain the square-root rule and every divisibility test, follow Euclid’s proof that primes never end, and prove facts about co-primes and twin primes.",{"depth":168,"revision":44,"title":1120,"subtitle":1121,"summary":1122,"estimatedMinutes":334,"reviewed":147,"reviewMethod":148},"Primes in the wild: cicadas, codes and unsolved puzzles","From insect life cycles and online banking to record primes, perfect numbers and problems nobody has solved","Take primes into the world: prime cicada cycles, the prime-based codes behind online payments, Mersenne primes and perfect numbers, Goldbach’s and the twin prime conjectures, Indian mathematicians, other number bases, olympiad puzzles and projects.",{"count":173,"sections":233,"levels":1124},{"foundation":235,"core":236,"stretch":176,"challenge":233},{"id":1126,"slug":1126,"title":1127,"question":1128,"promise":1129,"domains":1130,"areas":1131,"keywords":1132,"status":139,"layers":1153,"questionBank":1174},"properties-of-numbers","Properties of numbers","Why does 7 × 8 equal 8 × 7, and how can such rules make mental maths easy?","The closure, commutative, associative and distributive properties, the special roles of 0 and 1, and how they turn hard calculations into easy ones.",[11],[17],[1133,1134,1135,1136,1137,1138,1139,1140,1141,1142,1143,1144,1145,1146,1147,1148,1149,1150,1151,1152],"commutative","associative","distributive","closure","identity","additive identity","multiplicative identity","natural numbers","whole numbers","number line","mental maths","properties of zero","properties of one","division by zero","even and odd","counterexample","always sometimes never","area model","integers","clock arithmetic",[1154,1158,1162,1166,1170],{"depth":142,"revision":44,"title":1155,"subtitle":1156,"summary":1157,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Rules that numbers always follow","Turn-around facts, friendly groups, breaking apart and the magic of 0 and 1","Meet the properties of numbers through chairs, laddoos, kirana bills and socks: why 4 × 6 = 6 × 4, why you can add in any order, how breaking numbers apart makes sums easy, and what 0 and 1 do.",{"depth":150,"revision":44,"title":1159,"subtitle":1160,"summary":1161,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"The properties, precisely","Closure, commutative, associative and distributive laws, and the special numbers 0 and 1","State each property of whole numbers exactly, in words and with letters; see why it holds for + and × but fails for − and ÷; learn why division by zero is undefined; and use the properties for fast, reliable mental maths.",{"depth":156,"revision":44,"title":1163,"subtitle":1164,"summary":1165,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Always, sometimes or never?","Predict, test and explain: counterexamples, grouping gaps, parity patterns and shortcut showdowns","Test claims about whole numbers the way mathematicians do: predict, hunt for counterexamples, measure how badly subtraction and division fail to swap or regroup, discover patterns and shortcuts, and explain why the true ones must be true.",{"depth":162,"revision":44,"title":1167,"subtitle":1168,"summary":1169,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Why the rules must be true","Proofs with arrays and boxes, the distributive law behind every method, zero through history, and the road to algebra","Prove the commutative, associative and distributive laws for every whole number, see why long multiplication and divisibility tests work, show why division by zero would make 0 = 1, prove parity facts with letters, and meet the properties as the rules of algebra.",{"depth":168,"revision":44,"title":1171,"subtitle":1172,"summary":1173,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Properties beyond the whole numbers","Integers, fractions, clocks, computers, puzzles and the problems nobody has solved","Take the properties into new worlds: integers and fractions that repair closure, clock arithmetic, non-commutative everyday actions, rounding inside computers, olympiad puzzles built on parity and the distributive law, projects to try and open questions like Goldbach.",{"count":1175,"sections":385,"levels":1176},85,{"foundation":237,"core":212,"stretch":284,"challenge":174},{"id":1178,"slug":1178,"title":1179,"question":1180,"promise":1181,"domains":1182,"areas":1183,"keywords":1184,"status":139,"layers":1204,"questionBank":1225},"shape-and-space","Shape and space","What makes a square a square, and how many edges does a cube really have?","2D shapes and their properties, 3D solids and their faces, edges and vertices, nets, views from different sides, and symmetry.",[11],[29],[1185,1186,1187,1188,1189,1190,1191,708,1192,1193,1194,1195,1196,1197,1198,1199,1200,1201,1202,1203],"polygon","triangle","quadrilateral","circle","diagonals","cube","cuboid","pyramid","faces edges vertices","net","views","line symmetry","rotational symmetry","Euler","Platonic solids","tangram","tessellation","2D","3D",[1205,1209,1213,1217,1221],{"depth":142,"revision":44,"title":1206,"subtitle":1207,"summary":1208,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Shapes all around us","Flat shapes, solid shapes, and how to count, fold, view and mirror them","Meet 2D and 3D shapes through things you know: carrom boards, dice, laddoos, honeycombs, the Ashoka Chakra and the Taj Mahal. Learn to name polygons, count faces, edges and corners, unfold a box into a net, and find lines of symmetry.",{"depth":150,"revision":44,"title":1210,"subtitle":1211,"summary":1212,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Naming shapes precisely","Definitions, properties and the mix-ups they clear up","Give every shape an exact definition: polygons and diagonals, triangles by sides and angles, the quadrilateral family tree, the parts of a circle, perimeter, prisms and pyramids, nets, views and line symmetry, with worked examples and common mix-ups.",{"depth":156,"revision":44,"title":1214,"subtitle":1215,"summary":1216,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Test it, fold it, count it","Predictions and experiments with diagonals, triangles, nets, views, symmetry and π","Predict, then test: how fast diagonals multiply, which three sticks make a triangle, what polygon angles add up to, which statements are always true, the F + V − E pattern, which six-square shapes fold into a cube, symmetry in letters, measuring π and which shapes tile a floor.",{"depth":162,"revision":44,"title":1218,"subtitle":1219,"summary":1220,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Why shapes behave as they do","Proofs, edge cases and history: diagonals, angle sums, inequality, Euler and symmetry","Turn patterns into proofs: the diagonal formula, why angles add to 180° and (n − 2) × 180°, the triangle inequality, quadrilateral inheritance, why wheels are round, a sketch proof of Euler’s formula and where it fails, cube-net rules, symmetry orders, and the history of π.",{"depth":168,"revision":44,"title":1222,"subtitle":1223,"summary":1224,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Projects, puzzles and the wider world of shape","Platonic solids, all 11 cube nets, rotational symmetry, tilings, olympiad problems and open questions","Build the five Platonic solids and hunt all 11 cube nets, design rangoli with rotational symmetry, explore tangram paradoxes and semi-regular tilings, count a football, see geometry in Indian monuments and nature, solve olympiad-style problems, and meet questions still unsolved.",{"count":232,"sections":233,"levels":1226},{"foundation":284,"core":636,"stretch":284,"challenge":238},{"id":1228,"slug":1228,"title":52,"question":1229,"promise":1230,"domains":1231,"areas":1232,"keywords":1233,"status":139,"layers":1252,"questionBank":1273},"sound","Why does a drum you cannot touch still reach your ears?","Sound is a vibration travelling through air, water and solids. Learn what makes a sound high or low, loud or soft, why space is silent, and how your ears turn shaking air into music.",[41],[51],[1228,1234,1235,1236,1237,1238,1239,1240,1241,1242,1243,1244,1245,1246,1247,1248,1249,1250,1251],"vibration","wave","pitch","frequency","amplitude","loudness","decibel","echo","medium","ultrasound","hertz","eardrum","resonance","speed of sound","noise","music","sonar","vacuum",[1253,1257,1261,1265,1269],{"depth":142,"revision":44,"title":1254,"subtitle":1255,"summary":1256,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Everything that sounds is shaking","Find the vibration behind every sound, follow it to your ear, and learn why space is silent","Feel your own throat buzz, watch a tuning fork throw water, and follow the shaking from a tabla skin across the room to the hair cells in your ear. Meet pitch, loudness, echoes and the thunder rule, and find out why nothing at all can be heard in space.",{"depth":150,"revision":44,"title":1258,"subtitle":1259,"summary":1260,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Compressions, rarefactions and the wave equation","What is really travelling, how fast, and how the ear turns it into a signal","See what a sound wave actually is: a train of squashed and stretched air marching outwards. Meet longitudinal waves on a slinky, the equation v = f × λ, why steel beats air by seventeen times, how decibels multiply, and the engineering of the human ear.",{"depth":156,"revision":44,"title":1262,"subtitle":1263,"summary":1264,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Predict it, try it: resonance, echoes and everyday sound technology","Test resonance with a swing and a singing glass, then use echoes the way sonar, ultrasound, bats and dolphins do","Push a swing at the wrong rhythm, make a wine glass sing, and find the sympathetic strings that ring inside a sitar untouched. Time an echo the way sonar and a hospital scanner do, compare a bat's call with a dolphin's, and see why India's noise rules are stricter near a hospital than in a market.",{"depth":162,"revision":44,"title":1266,"subtitle":1267,"summary":1268,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Why resonance, harmonics and reverberation work the way they do","Damping, aeroelastic flutter, singing granite pillars, harmonics and a physicist with 300 cushions","Find out why resonance cannot grow forever, why two famous bridge wobbles had different causes, and why 56 granite pillars at Hampi ring with different notes. Meet Wallace Sabine, who found the reverberation formula with borrowed cushions, and the arithmetic of combining decibels.",{"depth":168,"revision":44,"title":1270,"subtitle":1271,"summary":1272,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Doppler shifts, digital recording and listening to the Earth","The physics of a passing siren, why your recorded voice sounds strange, and how earthquakes get located","Work out how much a siren's pitch shifts as it passes, find out why your recorded voice sounds strange (a real anatomical reason), and see why 44,100 Hz was not an arbitrary choice. Try two projects, solve combined puzzles, and use sound's own reasoning to locate an earthquake.",{"count":687,"sections":233,"levels":1274},{"foundation":388,"core":927,"stretch":337,"challenge":233},{"id":560,"slug":560,"title":1276,"question":1277,"promise":1278,"domains":1279,"areas":1280,"keywords":1281,"status":139,"layers":1298,"questionBank":1319},"Tides","Why does the sea climb up the beach and slide back, twice a day, forever?","The Moon's pull stretches the ocean into two bulges and Earth turns through them. Learn why there are two high tides a day, why they arrive later each day, and what makes a spring tide.",[63],[73],[1282,1283,1284,1285,1286,1287,1288,541,1289,1290,1291,1292,1293,1294,1295,1296,1297],"tide","high tide","low tide","spring tide","neap tide","tidal range","bulge","Moon","Sun","tidal bore","estuary","tide table","coast","fishing","Chandipur","Hooghly",[1299,1303,1307,1311,1315],{"depth":142,"revision":44,"title":1300,"subtitle":1301,"summary":1302,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Tides: the sea's daily rise and fall","Why the whole ocean leans towards the Moon, twice a day, forever","Meet the tide: not a wave but the whole sea rising and falling. Find out how the Moon's pull makes two bulges, why most coasts get two high tides a day, why the tide is 50 minutes later each day, and what spring and neap tides are.",{"depth":150,"revision":44,"title":1304,"subtitle":1305,"summary":1306,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"How the Moon builds two bulges","Difference, not strength: the mechanism behind every tide","Work out why a pull towards the Moon makes a bulge away from it, where 24 h 50 min comes from, why the Sun's tide is only 46% of the Moon's, and why the same Moon gives Kochi one metre and Bhavnagar ten.",{"depth":156,"revision":44,"title":1308,"subtitle":1309,"summary":1310,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Investigate: predicting, classifying and staying safe","Test the ideas from Understand against a real tide table, real coasts and real disasters","Predict and check a day of tide heights, learn to tell semidiurnal, diurnal and mixed tides apart, meet the Hooghly bore and storm surges, see how tidal power and INCOIS's predictions work, and test the funnelling and resonance ideas with real numbers.",{"depth":162,"revision":44,"title":1312,"subtitle":1313,"summary":1314,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Deepen: the mathematics and history behind a tide table","Newton, Laplace, harmonic waves, closed-pipe resonance, and the physics of a bore","Trace the two-hundred-year path from Newton's equilibrium theory to Laplace's ocean waves and Kelvin's tide-predicting machine, meet the harmonic constituents that a real tide is built from, derive why a bay resonates at a quarter wavelength, and quantify Earth's own solid and atmospheric tides.",{"depth":168,"revision":44,"title":1316,"subtitle":1317,"summary":1318,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Extend: deep time, deep space, and open questions","Tidal friction across hundreds of millions of years, tides on other worlds, and what is still unknown","Follow tidal friction from a subtle offset in Earth's bulge to a shorter Cretaceous day, a measurably receding Moon, tidal heating on Io, Europa and Enceladus, and a set of open questions and careers built on this one idea.",{"count":1320,"sections":385,"levels":1321},71,{"foundation":786,"core":283,"stretch":284,"challenge":174},[1323,1326,1328,1331,1333,1335,1337,1339,1341,1343,1345,1347,1350,1353,1355,1357,1359,1361,1363,1365,1367,1369,1371,1373,1375,1377,1379,1381,1383,1385,1387,1389,1391,1393,1395,1397,1399,1401,1403,1405,1407,1409,1411,1413,1415,1417,1419,1421,1423,1425,1427,1429],{"from":929,"to":489,"relation":1324,"reason":1325},"helps_understand","Place value is what makes column addition, carrying and long division work.",{"from":929,"to":287,"relation":1324,"reason":1327},"Reading, comparing and rounding numbers comes first when you sort data and round a mean.",{"from":929,"to":877,"relation":1329,"reason":1330},"related_to","Place-value charts are full of patterns: each place is ten times the one to its right.",{"from":1126,"to":489,"relation":1324,"reason":1332},"Commutative, associative and distributive properties are the shortcuts behind fast, accurate calculation.",{"from":1126,"to":980,"relation":1324,"reason":1334},"The distributive property explains why multiplication is done before addition and how brackets change a result.",{"from":1126,"to":877,"relation":1329,"reason":1336},"Many number patterns — like the sum of consecutive odd numbers — are properties of numbers in disguise.",{"from":489,"to":980,"relation":1324,"reason":1338},"Once each operation is reliable, the next question is which one to do first when several appear together.",{"from":489,"to":1077,"relation":1324,"reason":1340},"Testing whether a number is prime is just careful division: does anything divide it exactly?",{"from":489,"to":287,"relation":1324,"reason":1342},"Finding a mean means adding every value and dividing by how many there are.",{"from":980,"to":877,"relation":1329,"reason":1344},"A pattern rule such as 3 × n + 1 is an expression — you need the order of operations to use it.",{"from":1077,"to":588,"relation":1324,"reason":1346},"Prime factorisation is the fastest route to both the HCF and the LCM.",{"from":1077,"to":877,"relation":1348,"reason":1349},"contrasts_with","Primes famously refuse to follow a simple pattern, unlike even numbers, squares or multiples.",{"from":588,"to":877,"relation":1351,"reason":1352},"applied_in","Two repeating cycles line up again after their LCM — the pattern behind blinking lights and bus timetables.",{"from":588,"to":1178,"relation":1351,"reason":1354},"The largest square tile that fits a rectangular floor exactly has a side equal to the HCF of its length and width.",{"from":877,"to":1178,"relation":1329,"reason":1356},"Growing shape patterns — matchstick squares, dot triangles — are geometry and number at the same time.",{"from":1178,"to":739,"relation":1329,"reason":1358},"Every polygon is built from line segments, and its sides can be parallel or perpendicular.",{"from":1178,"to":180,"relation":1329,"reason":1360},"The corners of shapes are angles: a square has four right angles and a triangle's angles add to 180°.",{"from":739,"to":180,"relation":1324,"reason":1362},"An angle is two rays that share an end point; intersecting lines make angle pairs.",{"from":739,"to":828,"relation":1324,"reason":1364},"Constructions rely on drawing straight lines, perpendiculars and bisectors accurately.",{"from":180,"to":828,"relation":1324,"reason":1366},"Knowing angle types and pairs tells you what you are measuring and checks if your construction is sensible.",{"from":180,"to":287,"relation":1351,"reason":1368},"In a pie chart each slice's angle shows a share of the data: 360° stands for the whole.",{"from":828,"to":1178,"relation":1351,"reason":1370},"Drawing accurate triangles, squares and regular polygons needs measured or constructed angles.",{"from":287,"to":390,"relation":1351,"reason":1372},"A family's monthly electricity use varies; the mean, median and range of a year of bills show what is typical.",{"from":929,"to":390,"relation":1351,"reason":1374},"Power stations are rated in megawatts and India uses lakhs of crores of units a year: reading such numbers needs place value and the Indian system.",{"from":489,"to":390,"relation":1351,"reason":1376},"An electricity bill is units × rate per unit, plus fixed charges, minus subsidies — all four operations in one sheet of paper.",{"from":180,"to":390,"relation":1351,"reason":1378},"A generator's coil turns through 360° every cycle — 50 full turns a second on India's 50 Hz supply.",{"from":1077,"to":390,"relation":1351,"reason":1380},"The encryption that protects smart meters and grid control systems relies on the difficulty of factorising huge numbers into primes.",{"from":690,"to":340,"relation":1324,"reason":1382},"An eclipse is a shadow, and shadows need light that travels in straight lines.",{"from":690,"to":1030,"relation":1324,"reason":1384},"The Moon has no light of its own: we see the half of it the Sun is lighting.",{"from":690,"to":112,"relation":1351,"reason":1386},"The eye is a lens, a screen and a shutter — optics built out of living tissue.",{"from":690,"to":1228,"relation":1348,"reason":1388},"Both travel as waves and carry energy, but light needs no material and races a million times faster than sound.",{"from":1228,"to":112,"relation":1351,"reason":1390},"The ear turns shaking air into signals a nerve can carry: a drum, three tiny bones and a spiral of fluid.",{"from":541,"to":1030,"relation":1324,"reason":1392},"Gravity is what keeps the Moon in the orbit that produces the monthly cycle of phases.",{"from":541,"to":560,"relation":1324,"reason":1394},"Tides are gravity made visible: the Moon pulls the near ocean harder than the far ocean.",{"from":541,"to":340,"relation":1324,"reason":1396},"Eclipses happen only because the Sun, Earth and Moon move on fixed gravitational paths we can predict.",{"from":1030,"to":340,"relation":1324,"reason":1398},"Eclipses can only happen at new moon or full moon — the two phases where the three bodies line up.",{"from":1030,"to":560,"relation":1329,"reason":1400},"Spring and neap tides follow the phases: the biggest tides come at new and full moon.",{"from":112,"to":240,"relation":1324,"reason":1402},"Once you know where each organ sits, you can follow how they pass work to each other.",{"from":240,"to":541,"relation":1329,"reason":1404},"Bones, muscles and blood pressure are all built for a life spent pulling against Earth's gravity — which is why astronauts weaken in orbit.",{"from":439,"to":638,"relation":1324,"reason":1406},"The empires that grew out of the voyages shaped the constitution and the freedoms India wrote for itself afterwards.",{"from":439,"to":560,"relation":1351,"reason":1408},"Sailing ships left harbour on the tide, and monsoon winds and currents set the whole calendar of Indian Ocean trade.",{"from":439,"to":1030,"relation":1351,"reason":1410},"Before clocks and satellites, the Moon and stars were how a navigator knew where they were.",{"from":638,"to":287,"relation":1351,"reason":1412},"A census, an election result and a budget are all data: counted, summarised and argued over.",{"from":638,"to":929,"relation":1351,"reason":1414},"Election results and budgets are read in lakhs and crores — place value with real consequences.",{"from":690,"to":390,"relation":1329,"reason":1416},"A bulb, an LED and a solar panel are all conversions between electricity and light.",{"from":1228,"to":390,"relation":1329,"reason":1418},"Microphones and speakers turn sound into current and current back into sound.",{"from":439,"to":1178,"relation":1351,"reason":1420},"Maps, globes and navigation are geometry: a round Earth flattened onto paper without lying too much.",{"from":340,"to":180,"relation":1351,"reason":1422},"Whether an eclipse is total or partial comes down to angles: the Moon's tilted orbit and the apparent size of two discs.",{"from":560,"to":287,"relation":1351,"reason":1424},"A tide table is a data set: measure the water twice a day for years, and the pattern lets you predict it.",{"from":112,"to":287,"relation":1351,"reason":1426},"Heart rate, height and lung capacity across a class are real data to collect, average and compare.",{"from":541,"to":489,"relation":1351,"reason":1428},"Weight on another world is your mass times that world's gravity — multiplication with an astonishing answer.",{"from":240,"to":287,"relation":1351,"reason":1430},"Pulse and breathing rate before and after exercise are real class data to average, compare and graph.",[],[],[],{"layer":1435,"contentHash":2775,"dependencyHashes":2776,"approval":2777,"releaseId":2781,"sources":2782},{"schemaVersion":44,"conceptId":789,"locale":1436,"depth":156,"revision":44,"title":812,"subtitle":813,"summary":814,"objectives":1437,"estimatedMinutes":805,"plate":1443,"blocks":1469,"sourceIds":2770,"reviewStatus":2771,"authoring":2772},"en",[1438,1439,1440,1441,1442],"Plan a fair-test to compare how many paper clips different magnet types can lift, controlling for surface area and distance.","Predict which classroom materials will be magnetic, then test and classify them by observable evidence.","Investigate how heating, dropping or stroking a magnet changes its strength using a repeatable measurement method.","Compare the pattern of iron filings around bar and horseshoe magnets to argue for the shape of their magnetic fields.","Design an electromagnet and test how the number of wire coils affects its lifting strength, keeping current constant.",{"title":1444,"rows":1445},"Investigate",[1446,1448,1451,1454,1457,1460,1463,1466],{"label":1447,"value":1444},"Depth",{"label":1449,"value":1450},"Reading time","About 90 minutes",{"label":1452,"value":1453},"Chapters","12",{"label":1455,"value":1456},"Prior knowledge","Know poles, attraction\u002Frepulsion, magnetic materials, basic",{"label":1458,"value":1459},"Units used","Grams (g), centimetres (cm), turns (count), degrees Celsius",{"label":1461,"value":1462},"Activities","Four hands-on fair tests with household materials",{"label":1464,"value":1465},"Safety","Never swallow small magnets; hot objects need adult help",{"label":1467,"value":1468},"Source cited","Curiosity: Textbook of Science for Grade 6, Chapter 4 (Explo",[1470,1474,1480,1483,1489,1517,1522,1534,1552,1555,1558,1563,1566,1570,1596,1627,1631,1641,1654,1657,1667,1672,1675,1703,1716,1772,1776,1787,1792,1817,1822,1825,1830,1851,1868,1871,1880,1906,1911,1933,1936,1941,1944,1968,1972,1982,1999,2028,2033,2036,2040,2059,2062,2072,2093,2097,2113,2135,2138,2143,2146,2151,2168,2177,2181,2184,2204,2217,2221,2226,2229,2242,2267,2290,2294,2304,2324,2327,2334,2339,2342,2360,2369,2399,2404,2407,2412,2447,2457,2461,2472,2477,2480,2496,2499,2527,2531,2540,2553,2575,2580,2583,2677,2681,2692,2695,2711,2764],{"id":1471,"type":1472,"markdown":1473},"prose-1","prose","You already know that a magnet attracts iron and that like poles repel. But how do you *prove* one magnet is stronger than another? How do you know if heating really destroys magnetism, or if that was just a bad magnet to begin with?\n\nThis lesson turns your desk into a laboratory. You will control variables, repeat measurements, and let evidence settle arguments. By the end you will design your own electromagnet, test it fairly, and know exactly why your results came out the way they did.",{"id":1475,"type":1476,"title":1477,"eyebrow":1478,"navLabel":1479},"chapter-2","chapter","The Argument on the Train","Chapter 01","A disagreement",{"id":1481,"type":1472,"markdown":1482},"prose-3","Saket and Meera board the 8:17 Churchgate slow local every school morning. One rainy July Monday, Saket pulls out a flat, colourful fridge magnet—the kind with a Mumbai dabbawala printed on it. Meera counters with a tiny, silver cylinder no bigger than a pencil eraser, a neodymium magnet from her older brother's broken earphone case. \"Mine's stronger,\" Saket declares, waving the dabbawala magnet. \"It's bigger. Look, it can hold half my water bottle if I press it to the window frame.\" Meera laughs. \"Pressing doesn't count. Mine can pull a paper clip from two centimetres away without touching it at all. Your big flat one barely moves it from one centimetre.\" They argue all the way from Dadar to Mahim, but they have no winner. Both are measuring different things in different ways. Saket measures clinging force with pressure. Meera measures pulling distance through air. The argument is stuck because they never agreed on what \"stronger\" means or how to test it fairly. This chapter is about why that argument matters and how to build a test both would trust.",{"id":1484,"type":1485,"variant":1486,"title":1487,"markdown":1488},"callout-4","callout","definition","What is a fair test?","A **fair test** is a comparison where only one factor is changed at a time, while everything else that could affect the result is kept the same. The changed factor is called the **variable**. If you change more than one thing, you cannot know which change caused the difference. Repeating the test and recording results makes the evidence stronger than a single try.",{"id":1490,"type":1491,"title":1492,"items":1493},"steps-5","steps","The pattern every investigation follows",[1494,1498,1501,1505,1509,1513],{"title":1495,"tag":1496,"text":1497},"State the question","PLAN","Write what you want to find out in one sentence. Example: Which magnet lifts more paper clips?",{"title":1499,"tag":1496,"text":1500},"List the variables","Name what you could change (magnet size, shape, material) and what you will measure (number of clips, distance, time).",{"title":1502,"tag":1503,"text":1504},"Control what you can","FAIR","Keep the paper clips the same size, start from the same position, use the same motion each trial.",{"title":1506,"tag":1507,"text":1508},"Measure what changes","MEASURE","Use a number, not a feeling. Count clips, measure centimetres with a scale, time with a stopwatch.",{"title":1510,"tag":1511,"text":1512},"Repeat and record","REPEAT","Do each test at least three times. Write numbers in a table, not memory.",{"title":1514,"tag":1515,"text":1516},"Conclude with evidence","CONCLUDE","Say what happened and why your controls make you trust it. Offer what could still be uncertain.",{"id":1518,"type":1485,"variant":1519,"title":1520,"markdown":1521},"callout-6","misconception","\"I can just feel which is stronger\"","Human touch is surprisingly poor at comparing small forces. Pressing a magnet against your palm gives different results on a hot day, after exercise, or when you expect one result. Feel is useful for a quick guess, but it is **subjective evidence**: it changes with the person and the moment. Fair tests need **objective evidence**: numbers anyone can read and repeat.",{"id":1523,"type":1524,"title":1525,"problem":1526,"steps":1527},"worked-example-7","worked_example","Redesigning Saket and Meera's test","Saket claims his big fridge magnet is stronger because it holds a water bottle when pressed. Meera claims her tiny neodymium magnet is stronger because it pulls a paper clip from farther away. Design one fair test that settles which magnet has stronger magnetic pull.",[1528,1529,1530,1531,1532,1533],"Agree on one measure of 'strength.' Let us choose: how many identical paper clips can each magnet lift, hanging in a chain, without any other force helping?","Keep the test surface and motion identical. Place each magnet flat on a clean, dry steel lunch box lid. Lower paper clips one by one until the chain falls.","Use identical objects. Same brand, same size paper clips. Do not mix small and large clips.","Remove human pressure. Let the magnet rest under its own weight. Do not press or tilt.","Repeat three times for each magnet. Record the number of clips held each time. Average the three trials.","Compare the averages. The magnet with the higher average clip count showed stronger pull under these controlled conditions. Note: if one magnet is much thicker, its distance to the box lid differs slightly—this is a remaining uncertainty to report.",{"id":1535,"type":1536,"prompt":1537,"options":1538,"explanation":1551},"prediction-8","prediction","Saket and Meera now agree to test which magnet holds more paper clips. Before they start, Meera predicts the tiny neodymium magnet will win. Saket predicts the big fridge magnet will win. Which outcome would MOST strongly show that size alone does NOT determine magnetic strength?",[1539,1542,1545,1548],{"id":1540,"label":1541},"a","The big magnet holds more clips, and the tiny magnet holds none.",{"id":1543,"label":1544},"b","The tiny magnet holds more clips than the big magnet.",{"id":1546,"label":1547},"c","Both magnets hold exactly the same number of clips.",{"id":1549,"label":1550},"d","Neither magnet holds any clips at all.","Option B is correct. If the smaller magnet holds more clips, it directly contradicts Saket's assumption that bigger means stronger. This is the power of fair-test evidence: it can overturn expectations. Option C would be interesting but less decisive about size. Option A would support Saket's assumption without testing it. Option D would only show the test failed or the magnets were too far from the surface.",{"id":1553,"type":1472,"markdown":1554},"prose-9","Arguments like Saket and Meera's happen everywhere around magnets. In your kitchen, your classroom, at a scrap dealer's yard. Magnets are common, but judging their strength is tricky because magnets interact differently with different materials and at different distances. Without a fair test, you might buy a \"strong\" magnet that fails your need, or miss a tiny magnet perfect for your project. The eleven chapters after this one apply the same six-step pattern to questions across the whole world of magnetism: which materials stick, what weakens a magnet, how to make one, how Earth itself behaves like a magnet, and how electromagnets let engineers switch magnetism on and off. Each question deserves evidence you can trust, not just today's mood or yesterday's guess.",{"id":1556,"type":697,"prompt":1557},"reflection-10","Think of a time you argued with a friend about which object was \"better\" or \"stronger\"—a bat, a rubber band, a school bag. What did you measure? What did you ignore? Write two sentences about how a fair test would have changed the argument.",{"id":1559,"type":1476,"title":1560,"eyebrow":1561,"navLabel":1562},"chapter-11","Planning Your First Fair Test: How Many Paper Clips?","Chapter 02","Fair test one",{"id":1564,"type":1472,"markdown":1565},"prose-12","The first time Priya pulled out her new bar magnet on the Mumbai–Pune Deccan Queen, her brother Arjun snorted. \"That tiny thing? My horseshoe magnet from the school lab can lift way more.\"\n\n\"Prove it,\" said Priya.\n\nArjun grabbed a handful of paper clips from her pencil case and touched them to his horseshoe magnet. Six stuck. Priya touched her bar magnet to the same pile. Four stuck. \"See?\" Arjun grinned. \"Horseshoe wins.\"\n\nBut Priya frowned. She had used smaller clips, and Arjun had swept his magnet through the pile while she had only touched hers to the top. Also, her magnet had been lying in her hot bag while his had been in the air-conditioned compartment. Was the horseshoe really stronger, or had the test been unfair?\n\nIn science, a **fair test** is one where you change only the thing you want to compare and keep everything else exactly the same. If you do not control the conditions, your evidence is weak and your conclusion is shaky. In this chapter, you will learn how to plan a fair test to compare magnet strengths using nothing more than paper clips, patience, and a table.",{"id":1567,"type":1485,"variant":1486,"title":1568,"markdown":1569},"callout-13","Fair test and variables","A **fair test** is an investigation in which only one factor is changed at a time. The factor you deliberately change is the **independent variable**. The factor you measure to see the effect is the **dependent variable**. Everything else that could affect the result is a **controlled variable** — you keep it the same to make the comparison valid.",{"id":1571,"type":1491,"title":1572,"items":1573},"steps-14","Setting up your fair test",[1574,1578,1582,1585,1588,1592],{"title":1575,"tag":1576,"text":1577},"Choose your magnets","Independent variable","Pick 2–4 magnets to compare: bar, horseshoe, ring, or a small neodymium disc. Label each with masking tape so you do not mix them up.",{"title":1579,"tag":1580,"text":1581},"Pick one paper clip brand","Controlled variable","Use only one type of paper clip, same size and coating. Rusty or bent clips are not allowed. If you must switch brands mid-test, start over with all new trials.",{"title":1583,"tag":1580,"text":1584},"Decide the lifting method","Touch one clip to the magnet's pole, then dangle a second clip from the first, and so on, until the chain falls. Do not sweep through a pile.",{"title":1586,"tag":1580,"text":1587},"Fix the pole and orientation","Always use the same pole (say, the north pole) and hold the magnet the same way — vertical, horizontal, or flat on the table. Orientation changes the chain length.",{"title":1589,"tag":1590,"text":1591},"Count and record three trials","Dependent variable","For each magnet, build the longest chain you can, count the clips, and write the number in a table. Repeat twice more. Outliers happen; three trials help you spot them.",{"title":1593,"tag":1594,"text":1595},"Calculate the average","Analysis","Add the three trial numbers and divide by three. Use the average to compare magnets, not just your lucky best try.",{"id":1597,"type":1598,"caption":1599,"columns":1600,"rows":1606},"table-15","table","Sample data table for magnet strength comparison",[1601,1602,1603,1604,1605],"Magnet type","Trial 1 (clips)","Trial 2 (clips)","Trial 3 (clips)","Average (clips)",[1607,1612,1617,1622],[1608,1609,1610,1609,1611],"Bar magnet (red\u002Fblue)","4","5","4.3",[1613,1614,1614,1615,1616],"Horseshoe magnet (school lab)","6","7","6.3",[1618,1619,1619,1620,1621],"Neodymium disc (₹15 shop)","8","9","8.3",[1623,1624,1625,1624,1626],"Ring magnet (fridge toy)","3","2","2.7",{"id":1628,"type":1485,"variant":1519,"title":1629,"markdown":1630},"callout-16","\"More paper clips = always stronger\"","A horseshoe magnet usually lifts more paper clips than a bar magnet of the same material, but that is partly because it has two poles close together. A tiny neodymium disc can beat both. The shape concentrates the field; the material sets the ceiling. Shape and material are *different* variables, so comparing a bar magnet to a horseshoe without stating their sizes and materials is not a clean fair test. Always describe what you are actually holding, not just the magnet's shape.",{"id":1632,"type":1524,"title":1633,"problem":1634,"steps":1635},"worked-example-17","Ari's messy first test — what went wrong?","Ari tested three magnets: a school bar magnet, a broken toy horseshoe, and a refrigerator magnet. He used paper clips from two different boxes, tested the bar magnet in the hot kitchen and the others in the cool living room, and did only one trial each because \"it was boring.\" His bar magnet lifted 3 clips, the horseshoe 6, and the fridge magnet 1. He concluded: \"Horseshoe magnets are the strongest kind.\"",[1636,1637,1638,1639,1640],"Ari changed the magnet type (good) but also changed the paper clip brand, the room temperature, and the number of trials (bad). These are uncontrolled variables.","Temperature matters because heat can weaken a magnet — we will study this in Chapter 4. A hot bar magnet is not playing fair against a cool horseshoe.","Different paper clip brands have different masses and coatings. Heavier clips fall off sooner, making the magnet look weaker even if its field is unchanged.","Only one trial means a single shaky hand or bent clip ruins the evidence. Science repeats to catch accidents.","His conclusion overgeneralises from one broken toy to all horseshoe magnets. A fair test needs named magnets, controlled conditions, and repeated trials before any claim is made.",{"id":1642,"type":1536,"prompt":1643,"options":1644,"explanation":1653},"prediction-18","Priya has two identical-looking bar magnets, but one has a hairline crack across the middle. She plans one fair-test trial: she will lift paper clips with the cracked magnet and compare to the uncracked one. What is the biggest problem with her plan before she even starts?",[1645,1647,1649,1651],{"id":1540,"label":1646},"She should use iron filings instead of paper clips",{"id":1543,"label":1648},"She is only doing one trial, and the crack might change how the magnetic domains line up",{"id":1546,"label":1650},"Bar magnets cannot be cracked; they only snap in half",{"id":1549,"label":1652},"She should test both magnets at exactly 45°C in an oven","The correct answer is (b). One trial is too weak to trust, and a crack can break the magnetic domain alignment inside the material, possibly weakening or even splitting the field. We will learn about domains in Chapter 11. Option (a) switches tools without fixing the deeper issue. Option (c) is false — magnets can crack. Option (d) would add heat, an uncontrolled variable that weakens magnets, making the test even less fair.",{"id":1655,"type":1472,"markdown":1656},"prose-19","Once your table is filled and your averages calculated, you are ready to argue like Priya and Arjun — but with evidence instead of shouting. In the next chapter, you will apply this same fair-test discipline to a wider set of classroom materials. You will discover which ones are pulled by a magnet and which ones ignore it completely, building a classification that will matter for every chapter that follows.",{"id":1658,"type":1659,"title":1660,"points":1661},"summary-20","summary","What to carry forward",[1662,1663,1664,1665,1666],"A fair test changes only the independent variable and controls everything else.","In this investigation: magnet type = independent; paper clips lifted = dependent; clip brand, orientation, temperature, and number of trials = controlled.","Three trials plus an average protect you from outliers and shaky hands.","Shape and material are different variables; do not confuse them when comparing magnets.","Detail your method so someone else can repeat your test exactly — this is called reproducibility.",{"id":1668,"type":1476,"title":1669,"eyebrow":1670,"navLabel":1671},"chapter-21","Testing and Classifying Classroom Materials","Chapter 03","Predict and test",{"id":1673,"type":1472,"markdown":1674},"prose-22","Priya and Arun have finally reached school after their train argument about whether all metal objects must stick to a magnet. They brought a small neodymium magnet in their pencil box, and now their science teacher has challenged the whole class: *Before you test anything, write down what you think will happen.*\n\nThis is the heart of a fair test. A **prediction** is your best guess about what will happen, made *before* you collect evidence. If you guess after seeing the result, it is not a prediction — it is just a description. Priya believes that \"all metal things will stick.\" Arun thinks only \"some metal things will stick.\" Who is closer to the truth? The only way to settle it is to test objects one by one, record what actually happens, and let the evidence decide.\n\nIn this chapter you will learn a simple testing protocol — a step-by-step method — that lets you classify classroom materials by how they respond to a magnet. You will discover why some metals surprise you, and why \"metal\" is too broad a word to use when you really mean \"magnetic.\"",{"id":1676,"type":1491,"title":1677,"items":1678},"steps-23","A Reliable Testing Protocol",[1679,1683,1687,1691,1695,1699],{"title":1680,"tag":1681,"text":1682},"Predict first","before testing","List each object. Beside it, write 'will stick,' 'will not stick,' or 'not sure.' Do not change this after testing.",{"title":1684,"tag":1685,"text":1686},"Prepare the magnet","setup","Wipe the magnet clean. Check it sticks firmly to a known iron nail so you know the magnet is working.",{"title":1688,"tag":1689,"text":1690},"Approach slowly","test","Hold the magnet near the object. Do not smash it against the surface. Watch for any pull, even a slight tug.",{"title":1692,"tag":1693,"text":1694},"Test all parts","compound objects","If the object has different materials (a plastic pen with a metal clip), test each part separately and record separately.",{"title":1696,"tag":1697,"text":1698},"Record the evidence","record","Write exactly what happened: 'strong stick,' 'weak pull,' or 'no effect.' Evidence beats your first guess.",{"title":1700,"tag":1701,"text":1702},"Sort by result","classify","Group objects into 'strongly attracted,' 'weakly attracted,' and 'not attracted.' Do not group by what they are made of yet.",{"id":1704,"type":1536,"prompt":1705,"options":1706,"explanation":1715},"prediction-24","A shiny steel spoon, a copper coin, an aluminium foil ball, and a wooden pencil are on your desk. You have tested nothing yet. Which objects do you predict will be strongly attracted to a bar magnet?",[1707,1709,1711,1713],{"id":1540,"label":1708},"Steel spoon and copper coin",{"id":1543,"label":1710},"Steel spoon and aluminium foil ball",{"id":1546,"label":1712},"Steel spoon only",{"id":1549,"label":1714},"All four objects","Only the steel spoon should be strongly attracted. Steel is mostly iron, which is a magnetic material. Copper and aluminium are metals, but they are not attracted to a magnet at ordinary strength — a fact that surprises many people because 'metal' and 'magnetic' feel like the same category in everyday speech. The wooden pencil contains no iron, nickel, or cobalt, so it shows no attraction.",{"id":1717,"type":1598,"caption":1718,"columns":1719,"rows":1725},"table-25","Typical classroom materials and their magnetic response",[1720,1721,1722,1723,1724],"Object","Common material","Predicted response","Actual response","Evidence notes",[1726,1731,1736,1742,1746,1750,1755,1760,1764,1768],[1727,1728,1729,1729,1730],"Iron nail","Iron","Strong stick","Jumps toward magnet; holds weight",[1732,1733,1729,1734,1735],"Stainless steel spoon","Steel (varies by grade)","Varies: strong or none","Some spoons stick; kitchen '18\u002F10' often does not",[1737,1738,1739,1740,1741],"Brass door key","Copper + zinc alloy","May stick","No effect","Metal, but not magnetic — surprises many",[1743,1744,1739,1740,1745],"Aluminium foil","Aluminium","Very light; even a tiny pull would show; none does",[1747,1748,1739,1740,1749],"Copper wire","Copper","Shiny metal, no attraction",[1751,1752,1753,1740,1754],"Cobalt-blue glass bead","Glass with cobalt pigment","Unclear","Cobalt *element* is magnetic, but locked in glass",[1756,1757,1729,1758,1759],"Nickel coin (old)","Nickel or nickel alloy","Usually weak to strong","Modern coins vary; pure nickel is magnetic",[1761,1762,1740,1740,1763],"Plastic ruler","Plastic polymer","Confirms prediction easily",[1765,1766,1740,1740,1767],"Wooden pencil","Wood + graphite","Graphite is carbon; not magnetic",[1769,1770,1729,1729,1771],"Paper clip","Steel wire","Classic test; use to verify your magnet works",{"id":1773,"type":1485,"variant":1519,"title":1774,"markdown":1775},"callout-26","\"All metals are magnetic\" — a common trap","Many learners — and adults — say \"metal\" when they mean \"iron-like.\" This is a **model** of how people talk, not how nature works. In reality, only three common elements are strongly magnetic: **iron**, **nickel**, and **cobalt**. Some mixtures called **alloys** (like steel) can also be magnetic if they contain enough iron and are processed the right way. But copper, aluminium, zinc, lead, silver, and gold are all metals with *no* attraction to a magnet. The word \"metal\" describes how shiny or bendy something is, or how it conducts electricity. \"Magnetic\" describes how it responds to a magnetic field. These two ideas overlap, but they are not the same shape. Using \"metal\" to mean \"magnetic\" is like using \"fruit\" to mean \"sweet\" — most fruits are sweet, but cucumbers and tomatoes are fruits too, and they are not sweet at all.",{"id":1777,"type":1524,"title":1778,"problem":1779,"steps":1780},"worked-example-27","Sorting Priya and Arun's Bag of Objects","Priya and Arun emptied their bags: a steel water bottle, a copper wire from a broken circuit, an aluminium foil snack wrapper, a nickel-coated key ring, and a plastic comb. After testing each object with a bar magnet, how should they classify them by evidence?",[1781,1782,1783,1784,1785,1786],"Test the steel water bottle: the magnet snaps to the side. Record: STRONGLY ATTRACTED. Material contains iron in steel.","Test the copper wire: the magnet rests against it with no pull. Record: NOT ATTRACTED. Copper is a non-magnetic metal.","Test the aluminium foil: crumple it so it is easy to grip. The magnet shows no tug. Record: NOT ATTRACTED. Aluminium is a non-magnetic metal.","Test the nickel-coated key ring: the magnet sticks firmly. Record: STRONGLY ATTRACTED. Nickel coating or nickel alloy is magnetic.","Test the plastic comb: nothing happens. Record: NOT ATTRACTED. Plastic contains no iron, nickel, or cobalt.","Now classify by the *evidence*, not by the object name: Group 1 (strongly attracted): steel bottle, nickel key ring. Group 2 (not attracted): copper wire, aluminium foil, plastic comb. Notice that three objects were metals, but only two were magnetic.",{"id":1788,"type":1485,"variant":1789,"title":1790,"markdown":1791},"callout-28","nuance","Stainless steel: when metal looks identical but behaves differently","Your school might have two stainless steel spoons that look exactly the same. One sticks to a magnet; the other does not. This happens because **stainless steel is a family of alloys**, not one single recipe. Some stainless steels contain nickel and chromium in proportions that let iron keep its magnetic domains — these stick. Others, called **austenitic** stainless steels, are designed to resist magnets for kitchen and medical use — these do not stick. This is why you cannot predict magnetism from the word \"steel\" alone. You must *test*.",{"id":1793,"type":1794,"itemId":1795,"prompt":1796,"check":1797,"hints":1809,"feedback":1814},"practice-29","practice","magnets.p001","You find a mystery object in the classroom: silvery, shiny, and cold to touch. You think it might be made of aluminium or steel. You have a bar magnet. What is the quickest fair-test to decide, and what result means what?",{"kind":1798,"options":1799,"correct":1808},"choice",[1800,1802,1804,1806],{"id":1540,"label":1801},"Heat the object; if it melts, it is aluminium",{"id":1543,"label":1803},"Slowly bring the magnet near; strong stick means steel, no stick means aluminium",{"id":1546,"label":1805},"Weigh it; steel is always heavier than aluminium",{"id":1549,"label":1807},"Drop it; steel bounces higher than aluminium",[1543],[1810,1811,1812,1813],"Melting requires dangerous heat and both metals melt above 600 °C — not a classroom test.","Magnetism is a property that cleanly separates most steel (magnetic) from aluminium (not magnetic).","Weight depends on size; a large aluminium block can outweigh a small steel washer.","Bounciness depends on shape, not just material.",{"correct":1815,"incorrect":1816},"Correct. Magnetism is the reliable divider here. A strong stick suggests iron-containing steel; no attraction points toward aluminium or another non-magnetic metal. Always test with the same magnet and same slow approach for a fair comparison.","Think about which test gives a clear yes\u002Fno answer and can be done safely at a desk. Magnetism separates these two metals directly, without needing heat, scales, or guesswork about shape.",{"id":1818,"type":1476,"title":1819,"eyebrow":1820,"navLabel":1821},"chapter-30","What Weakens a Magnet? Heat, Drop and Strike","Chapter 04","Damage tests",{"id":1823,"type":1472,"markdown":1824},"prose-31","By the time you reach chapter 4, you already know how to test if something is magnetic and how to compare strengths. Now imagine this: your team has a strong bar magnet that lifts twelve paper clips. Your cousin leaves it on a sunny windowsill in May. Your little brother uses it to hold drawings on the fridge, and it falls twice a day. Your uncle once tried to \"fix\" a dented magnet by tapping it with a hammer. Each of these stories raises the same question: does a magnet stay a magnet forever, or do everyday events slowly kill it?\n\nThis chapter is a fair-test investigation. You will change one condition at a time, predict the outcome, measure the evidence, and compare it to your starting point. The tool is simple: count how many standard paper clips the magnet can lift straight off the table. We call this the **baseline** — the measurement before anything is changed. Every later test is compared back to this baseline. A **fair test** means you change only the one factor you are studying; everything else stays identical. Same magnet, same clips, same lifting motion, same room.\n\nWe will test three conditions that Curiosity: Textbook of Science for Grade 6, Chapter 4 (Exploring Magnets) warns about: heat, dropping, and hammering. The surprise is that some damage is permanent and some is not, and the evidence is hidden in how the tiny internal structure responds.",{"id":1826,"type":1485,"variant":1827,"title":1828,"markdown":1829},"callout-32","model_limit","The Paper-Clip Count Is a Model","Counting paper clips gives a useful *comparison* of strength, but it is not a precise scientific unit. Magnet strength is measured in teslas (T) with proper instruments. We use paper clips because they are cheap, identical, and easy to count at home. Always label a simplified tool as a model, so you do not confuse \"lifts eight clips\" with \"has eight units of magnetism.\"",{"id":1831,"type":1491,"title":1832,"items":1833},"steps-33","Setting Your Baseline Before Any Test",[1834,1838,1841,1845,1848],{"title":1835,"tag":1836,"text":1837},"Mark the magnet","control","Use tape to label one pole N and the other S. Always lift with the same pole facing down so orientation is constant.",{"title":1839,"tag":1836,"text":1840},"Choose standard clips","Pick plain steel paper clips of one size. Rusty or plastic-coated clips have different masses and may stick less.",{"title":1842,"tag":1843,"text":1844},"Lift gently","measure","Lower the magnet until it touches a clip on the table, then lift straight up slowly. Count how many hang in a chain.",{"title":1846,"tag":1697,"text":1847},"Record three trials","Shake the clips off, wait ten seconds, repeat. Write the three numbers. The middle value is your baseline.",{"title":1849,"tag":1836,"text":1850},"Check the room","Note the room temperature. Hotter rooms already give slightly weaker lifts, so keep conditions steady.",{"id":1852,"type":1536,"prompt":1853,"options":1854,"explanation":1867},"prediction-34","You have a bar magnet with a baseline of 10 paper clips. You place it in 60°C water for five minutes, let it cool to room temperature, and retest. What do you predict?",[1855,1858,1861,1864],{"id":1856,"label":1857},"ten","Still 10 clips — water cannot hurt a solid magnet",{"id":1859,"label":1860},"eight","About 8 clips — some weakening, but small",{"id":1862,"label":1863},"four","Around 4 clips — heat badly weakens magnets",{"id":1865,"label":1866},"zero","0 clips — the magnet is completely ruined","The correct expectation is closer to 8 clips at 60°C for many common classroom magnets: noticeable weakening, but far from total loss. Heat adds energy to the internal structure called **magnetic domains** (tiny regions where atomic magnets line up). At 60°C, some domains jumble, so fewer line up with the field. At 80°C the drop is larger. Every material has a **Curie temperature** where domains randomise completely and magnetism disappears; for iron this is 770°C, far above boiling water, but weaker grades of bar magnet can show partial loss well below that.",{"id":1869,"type":1472,"markdown":1870},"prose-35","Now study the table carefully. The heat trend is smooth: hotter water, fewer clips. That pattern is called a **trend** — a consistent direction in data. The mechanical tests lookdifferent. Dropping is gentler than hammering, so the drop lost three clips while hammering lost six. But here is the deeper puzzle: after the hammer test, leave the magnet alone for two days and retest. Some groups find it recovers one or two clips. Why would a battered magnet partially heal?\n\nThe answer lies in those magnetic domains again. Inside the metal, billions of tiny atomic magnets normally point the same way, adding up to one strong bar magnet. A sharp shock from a hammer can knock some domains sideways or even flip them to point the opposite way. Domains pointing against the majority cancel out some of the total strength. However, in some **hard magnetic materials**, left alone, a few domains slowly drift back toward the majority direction. The recovery is usually small and never full. In **soft magnetic materials**, like the iron core inside a transformer, domains jumble easily and the magnet nearly dies. Material matters enormously, which is why you must always test the same magnet, not swap in a new one.",{"id":1872,"type":1524,"title":1873,"problem":1874,"steps":1875},"worked-example-36","Did the Heat Test Use a Fair Test? Check the Setup","One student heated her magnet in 100°C boiling water for five minutes, then immediately lifted paper clips while the magnet was still wet and hot. She found only 2 clips and concluded \"heat destroys magnetism.\" Her friend pointed out a problem. What is it, and how should she redo the test?",[1876,1877,1878,1879],"Identify the changed factor. The student wanted to test temperature effect, but she also changed wetness and temperature at the moment of lifting. Wet clips may stick differently, and a hot magnet has more thermal motion in the metal.","Separate the variables. She should cool the magnet back to room temperature and dry it completely before retesting. Then only temperature history differs from baseline, not present temperature or moisture.","Control the cooling. Place the hot magnet on a wooden surface in the same room as baseline tests. Wait until it feels room-temperature to the back of your hand.","Retest with the same pole, same clips, same lifting speed. Record the new count and compare to baseline, not to the unfair hot-and-wet measurement.",{"id":1881,"type":1794,"itemId":1882,"prompt":1883,"check":1884,"hints":1899,"feedback":1903},"practice-37","magnets.p002","A student baselines a magnet at 12 clips. He drops it 10 times from 30 cm and retests at 9 clips. Then he hammers it 10 times and retests at 4 clips. Two days later he retests and gets 5 clips. He claims \"magnets get stronger over time after damage.\" Is his conclusion supported? Pick the best answer.",{"kind":1798,"options":1885,"correct":1898},[1886,1889,1892,1895],{"id":1887,"label":1888},"yes","Yes — the magnet healed itself completely",{"id":1890,"label":1891},"partial","Partially — some recovery is possible, but the baseline of 12 was never reached again",{"id":1893,"label":1894},"no","No — 5 clips is random error, not real recovery",{"id":1896,"label":1897},"wrong","Wrong — he should have used a different magnet for the retest",[1890],[1900,1901,1902],"Compare the final 5 to the two previous numbers, not just to the hammer result.","Consider whether domains can partially re-align.","A fair test uses the same magnet; a different magnet would break the comparison.",{"correct":1904,"incorrect":1905},"Right. The data shows partial recovery from 4 to 5 clips, probably some domains re-aligning. But 5 is far below the baseline 12, so \"healed completely\" is false. The trend supports limited, not full, recovery.","Look again. The magnet never returns to 12 clips, so \"healed completely\" is wrong. The jump from 4 to 5 is small but consistent across many groups, so calling it random ignores the domain explanation. Using the same magnet is correct fair-test practice.",{"id":1907,"type":1485,"variant":1908,"title":1909,"markdown":1910},"callout-38","careful","Safety with Hot Water and Hammers","Adult supervision is essential for boiling-water tests. Use tongs, not fingers, to remove the magnet. Hammer tests should strike wood placed over the magnet, never the magnet directly on a hard anvil, to avoid shattering. Wear eye protection. Small magnet chips are dangerous if swallowed; keep them away from young children.",{"id":1912,"type":1913,"tone":1914,"items":1915},"spec-39","spec","amber",[1916,1920,1923,1926,1929],{"label":1917,"big":1918,"value":1919},"Baseline clips","10","Middle of three trials with same pole, same clips, dry conditions",{"label":1921,"big":1619,"value":1922},"Heat loss at 100°C","Clips lost after 5 min boiling, cooled to room temperature (example data)",{"label":1924,"big":1624,"value":1925},"Drop loss","Typical clips lost after 10 falls from 30 cm (example data)",{"label":1927,"big":1614,"value":1928},"Hammer loss","Typical clips lost after buffered taps (example data)",{"label":1930,"big":1931,"value":1932},"Domain size","~0.01 mm","Typical width of a magnetic domain in iron; invisible without microscopes, detected by iron-filing patterns instead",{"id":1934,"type":697,"prompt":1935},"reflection-40","Look around your home: where are magnets stored near heat (stove, sunlight, laptops) or where they might fall? List two places where moving or shielding a magnet could make it last longer. What is one thing you cannot easily protect it from, and why does that not worry you for fridge magnets?",{"id":1937,"type":1476,"title":1938,"eyebrow":1939,"navLabel":1940},"chapter-41","Seeing the Field: Iron Filings as Evidence","Chapter 05","Field patterns",{"id":1942,"type":1472,"markdown":1943},"prose-42","Have you ever watched iron filings dance around a magnet? In Chapter 3, you sorted classroom materials into magnetic and non-magnetic piles. Now you will ask a deeper question: *where* exactly is the magnetic pull strong, weak, or barely there?\n\nScientists cannot see magnetic force directly, so they need visible evidence. Iron filings — tiny slivers of iron that you can buy in a ₹15 packet at most school-supply shops — become temporary magnets when they are near a real magnet. Each filing turns into a tiny compass needle, swinging until it lines up with the local magnetic force. Where many filings crowd together and stand on end, the field is strong. Where they lie flat and scattered, the field is weak. Clusters and gaps are your evidence.\n\nIn this chapter you will compare three magnet shapes: a straight bar magnet, a horseshoe magnet, and a ring magnet. You will predict, test, and use the filing pattern to argue about where the invisible field goes. Remember: what you see on paper is only a *slice* — a flat cross-section — of a three-dimensional invisible structure. We will label it honestly as a model, not the full picture.",{"id":1945,"type":1491,"title":1946,"items":1947},"steps-43","How to Map a Magnetic Field with Iron Filings",[1948,1952,1956,1960,1964],{"title":1949,"tag":1950,"text":1951},"Set up","Prepare","Place the magnet flat on a table. Lay a clean white A4 sheet over it so the magnet is hidden underneath. No tape on top — you need to tap later.",{"title":1953,"tag":1954,"text":1955},"Sprinkle","Add filings","Hold the iron-filing packet about 15 cm above the paper. Tap the packet gently so filings fall like light rain. Cover the whole page, but do not dump a thick pile.",{"title":1957,"tag":1958,"text":1959},"Tap and watch","Reveal pattern","Lightly tap the paper with a pencil or finger. Filings will jump, spin, and settle into curved chains. Stop when the pattern is clear but before the paper slides.",{"title":1961,"tag":1962,"text":1963},"Sketch fast","Record","Trace the main lines and dense patches onto a second sheet before anyone bumps the table. Label N and S from the magnet underneath.",{"title":1965,"tag":1966,"text":1967},"Clean up","Restore","Lift the paper carefully and bend it to pour filings back into the packet. Keep filings dry; rusted filings stick and lie.",{"id":1969,"type":1485,"variant":1827,"title":1970,"markdown":1971},"callout-44","The Flat-Paper Trap: Why This Is Only a Model","Iron filings on paper show you a **two-dimensional slice** of a **three-dimensional field**. The real field also rises above and sinks below the paper. If you could freeze filings in a clear jelly block, you would see the lines bulge out of the page like a doughnut around a ring magnet, or arc over and under a bar magnet like a rainbow. Always label your iron-filing sketch as a *model* or *cross-section*. Saying 'the field is flat lines on paper' is a simplification, not the full truth. Curiosity: Textbook of Science for Grade 6, Chapter 4 shows the side-view diagram for this reason.",{"id":1973,"type":1524,"title":1974,"problem":1975,"steps":1976},"worked-example-45","Comparing Field Strength from Filing Density: A Scrapyard Case","A scrapyard owner has two magnets: a long thin bar magnet and a horseshoe magnet of the same weight. She wants to lift heavy iron plates from a pile. From iron-filing tests, the bar magnet shows dense clusters only at its two ends, with almost no filings in the middle. The horseshoe magnet shows dense, straight, parallel filing rows across its whole gap. Which magnet should she choose, and why?",[1977,1978,1979,1980,1981],"Identify the evidence: filing density maps field strength. Dense filings mean strong field; sparse filings mean weak field.","Map the bar magnet: strong only at poles, weak middle. The total 'strong zone' is two small spots.","Map the horseshoe magnet: strong field fills the entire gap between poles. The 'strong zone' is a broad, uniform strip.","Connect to the job: lifting a heavy plate needs a large area of strong pull, not two pinpoints. A plate might slip off a bar magnet's middle but sit securely across a horseshoe gap.","Conclusion: choose the horseshoe magnet. The parallel, dense filing pattern predicted a large, usable zone of strong field — evidence matched the practical need.",{"id":1983,"type":1536,"prompt":1984,"options":1985,"explanation":1998},"prediction-46","You sprinkle iron filings on a paper above a ring magnet and tap gently. Where will the filings be MOST densely packed and standing nearly upright?",[1986,1989,1992,1995],{"id":1987,"label":1988},"rim","Along the outer curved rim of the ring",{"id":1990,"label":1991},"faces","On the two flat top and bottom faces near the hole",{"id":1993,"label":1994},"middle-hole","Exactly at the centre of the hole, floating in air",{"id":1996,"label":1997},"random","Randomly everywhere, because a ring has no poles","The correct answer is 'On the two flat top and bottom faces near the hole.' A ring magnet's poles are its flat faces, not its rim. Field lines leave one face, loop through the hole, and re-enter the other face. Filings near those faces feel the strongest, most directed pull and stand upright in dense brushes. The rim has some field but it is weaker and more spread out. Filings cannot float in air, so the hole centre stays empty unless the field is strong enough to pull filings inward from the edges — which does happen, creating the characteristic loop pattern.",{"id":2000,"type":1598,"caption":2001,"columns":2002,"rows":2007},"table-47","Iron-filing patterns: what to look for and what it means",[2003,2004,2005,2006],"Magnet shape","Filing pattern you see","Field strength clue","Real-life use",[2008,2013,2018,2023],[2009,2010,2011,2012],"Bar magnet","Curved lines from N to S, sparse middle","Strongest at two ends (poles)","Compass needles, simple demonstrations",[2014,2015,2016,2017],"Horseshoe magnet","Straight parallel rows in the gap","Strong, uniform across gap","Scrapyard cranes, lab clamps",[2019,2020,2021,2022],"Ring magnet","Loops through hole, curves outside","Strong at flat faces, contained","Speakers, motors, magnetic bearings",[2024,2025,2026,2027],"Two bar magnets (N-N facing)","Filings bend away from gap; gap stays sparse","Repulsion zone between like poles","Maglev train levitation (model)",{"id":2029,"type":1476,"title":2030,"eyebrow":2031,"navLabel":2032},"chapter-48","Making and Losing a Magnet by Stroking","Chapter 06","Create and test",{"id":2034,"type":1472,"markdown":2035},"prose-49","You have probably seen a tailor or your grandmother run a steel needle through their hair before threading it. That simple motion can leave the needle slightly magnetic, enough to pick up another needle. But how exactly does stroking turn an ordinary steel needle into a magnet? And does stroking it more times make it stronger? In this chapter you will test the stroking method like a real investigator, controlling every variable so that only the number of strokes changes. You will also find out why a homemade magnet fades over time — and why heating it brings that fading forward.\n\nThe idea you are testing is the **domain theory of magnetism**, a model we introduced earlier. In this model, a piece of steel contains tiny regions called **domains**, each with its own tiny north and south pole. In an unmagnetised needle these domains point in random directions, so their effects cancel out. Stroking with a strong magnet nudges more and more domains to line up in the same direction. The more strokes, the more domains align — up to a limit. That is your prediction to test.",{"id":2037,"type":1485,"variant":1827,"title":2038,"markdown":2039},"callout-50","A model, not a photograph","The domain model is a useful picture, but no one has ever photographed an individual domain inside a sewing needle. Scientists infer domains from larger-scale behaviour — like how a magnetised needle behaves differently from an unmagnetised one. We label this a **model** because it explains the pattern, not because we have seen the domains directly.",{"id":2041,"type":1491,"title":2042,"items":2043},"steps-51","The single-stroke method, done correctly",[2044,2047,2050,2053,2056],{"title":2045,"text":2046},"Prepare the needle","Choose a plain steel sewing needle. Test it first: try to lift steel pins with it. It should fail — this confirms it starts unmagnetised.",{"title":2048,"text":2049},"Mark the poles","Hold the north pole of a strong bar magnet at the needle’s eye (the flattened end). The south pole should point toward the needle’s point.",{"title":2051,"text":2052},"Stroke steadily","Drag the bar magnet along the needle from eye to point in one smooth motion. Keep the magnet tilted so the same pole (north) stays in contact.",{"title":2054,"text":2055},"Lift and return high","At the end of each stroke, lift the magnet well away to the side and bring it back above the starting position. Do not slide it backward along the needle.",{"title":2057,"text":2058},"Repeat with count","Count each complete stroke. Needle A gets 5 strokes; Needle B gets 50 strokes. Both use identical stroking direction.",{"id":2060,"type":1472,"markdown":2061},"prose-52","Why lift the magnet away at the end of each stroke? If you slide the magnet back along the needle, the opposite pole rubs the needle the wrong way and partly reverses the alignment you just created. The lift-and-return keeps every stroke working in the same direction. This is a control on your experiment: both needles feel the same pole moving the same way, differing only in how many times it happens.",{"id":2063,"type":1524,"title":2064,"problem":2065,"steps":2066},"worked-example-53","Counting strokes and predicting lift","Rohan strokes Needle A 5 times and Needle B 50 times. He predicts Needle B will lift more pins because more strokes align more domains. He tests both needles immediately. Needle A lifts 3 pins; Needle B lifts 12 pins. One week later, without re-stroking, he repeats the test. What should he expect, and why?",[2067,2068,2069,2070,2071],"Prediction: Needle B should still lift more pins than Needle A, but both numbers should drop.","Reason: More strokes initially create stronger alignment, so Needle B retains an advantage.","Time allows thermal energy to jostle domains. Some domains drift back to random directions, weakening both needles.","The needle with more aligned domains (Needle B) has 'further to fall' but starts from a higher level, so it stays stronger.","Rohan records: Needle A now lifts 1 pin; Needle B now lifts 7 pins. The gap narrowed, but the ranking held.",{"id":2073,"type":1598,"caption":2074,"columns":2075,"rows":2081},"table-54","Rohan’s controlled stroking experiment, recorded immediately and after 7 days",[2076,2077,2078,2079,2080],"Needle","Strokes given","Pins lifted: Day 0","Pins lifted: Day 7","Change",[2082,2086,2090],[2083,1610,1624,2084,2085],"A","1","–2",[2087,2088,1453,1615,2089],"B","50","–5",[2091,2092,2092,2092,2092],"Control (unstroked)","0",{"id":2094,"type":1485,"variant":1908,"title":2095,"markdown":2096},"callout-55","Heating is an accelerator, not magic","Gently warming a magnetised needle over a candle flame (use tongs, not fingers) makes it lose magnetism faster than sitting in a drawer. The heat adds energy that lets domains tumble out of alignment. This is the same process as slow fading, just sped up. It is not a different process, and it does not prove the needle was never a true magnet.",{"id":2098,"type":1536,"prompt":2099,"options":2100,"explanation":2112},"prediction-56","Rohan now takes Needle B (50 strokes, 7 pins after one week) and heats it gently for 20 seconds. How many pins should it lift immediately after cooling?",[2101,2104,2107,2110],{"id":2102,"label":2103},"more","More than 7, because heat rearranges domains into better order",{"id":2105,"label":2106},"same","Still 7, because heat has no effect on magnetism",{"id":2108,"label":2109},"fewer","Fewer than 7, because heat randomises aligned domains",{"id":1865,"label":2111},"Exactly zero, because any heat destroys a magnet completely","The correct answer is 'fewer than 7'. Heat gives energy to the domains, letting them tumble out of alignment. The magnet weakens but may not drop to zero instantly — that depends on temperature, time and material. 'Exactly zero' is too extreme; 'more' confuses heat with stroking; 'same' ignores the well-tested effect of temperature on magnetic retention.",{"id":2114,"type":1794,"itemId":2115,"prompt":2116,"check":2117,"hints":2128,"feedback":2132},"practice-57","magnets.p003","A student strokes a steel needle 100 times and it lifts 15 pins. She then stores it for two weeks and retests. Choose the most reasonable result.",{"kind":1798,"options":2118,"correct":2127},[2119,2121,2123,2125],{"id":1540,"label":2120},"18 pins",{"id":1543,"label":2122},"15 pins",{"id":1546,"label":2124},"10 pins",{"id":1549,"label":2126},"0 pins",[1546],[2129,2130,2131],"Think about what happens to aligned domains over time without the strong magnet present.","The domains do not all flip instantly, but random motion works against alignment.","Compare your choice to Rohan’s data: his 50-stroke needle dropped from 12 to 7 pins.",{"correct":2133,"incorrect":2134},"Yes. Some domains randomise over time, so strength drops but does not usually vanish immediately. Ten pins is a reasonable decline.","Look again. Without re-stroking, domains drift toward randomness. Strength falls, but a total collapse to zero in two weeks is less likely than partial fading.",{"id":2136,"type":1472,"markdown":2137},"prose-58","Your investigation shows that stroking is not an all-or-nothing switch. Magnetism by stroking is **induced magnetism** — the strong bar magnet creates it in the steel needle without ever touching the needle with wires or batteries. The strength depends on how many strokes you apply, the pole you use and the material you stroke. Steel works well because its domains can align but do not flip back instantly; soft iron aligns easily but also loses alignment quickly, making it better for temporary electromagnets than for keepsake bar magnets.\n\nIn the next chapter you will step far outside the laboratory and discover that Earth itself behaves like a giant bar magnet. No stroking required, no iron bar to carry — just a spinning planet with a molten core. The compass needle you magnetised today already knows this secret, and you are about to learn how.",{"id":2139,"type":1476,"title":2140,"eyebrow":2141,"navLabel":2142},"chapter-59","Earth the Magnet: No Wires, No Bar, No Batteries","Chapter 07","Earth's field",{"id":2144,"type":1472,"markdown":2145},"prose-60","Imagine you are on a trek in the Western Ghats, far from any town. No mobile tower, no power lines, no fridge magnets in your bag. You pull out a small compass to find which way to walk. The needle swings, settles, and points north. But there is nothing around you — no wire, no battery, no bar magnet. What is pushing that tiny needle into line?\n\nIn Chapter 2 you hung a bar magnet on a thread and watched it swing until one end pointed north. A compass needle is itself a small magnet, shaped like a arrow and mounted so it turns freely. Left alone, it too lines up north-south, over and over, anywhere on Earth. That reliable pattern is the clue we need. The only way a small magnet can keep pointing the same direction across continents and oceans is if the entire planet is acting like one enormous magnet. In this chapter we treat that claim as a hypothesis and look for evidence. We will use a suspended magnet, a compass, and a simple model to argue that Earth carries a magnetic field — and we will face a puzzle about which pole is which.",{"id":2147,"type":1485,"variant":2148,"title":2149,"markdown":2150},"callout-61","observation","The reliable alignment test","A single observation could be luck. But travellers, sailors, and trekkers have tested this for centuries: a freely balanced magnetic needle points north-south in Kerala, in Ladakh, on a boat in the Bay of Bengal, and in your school corridor. Repeating the test under many conditions is one way scientists build confidence that the cause is large and steady, not local and accidental.",{"id":2152,"type":2153,"title":2154,"items":2155},"timeline-62","timeline","From floating needle to global magnet",[2156,2160,2164],{"time":2157,"title":2158,"text":2159},"~1088 CE","Shen Kuo describes compass use","Chinese scholar Shen Kuo records that a magnetised needle, floated on water or hung by silk thread, points south. He notes the direction is not perfectly true, hinting at more than one reference point.",{"time":2161,"title":2162,"text":2163},"1269","Peregrinus maps pole directions","French crusader Pierre de Maricourt (Peregrinus) draws a map of how magnetised needles arrange around a spherical lodestone. He shows they converge at two opposite points, like lines of longitude.",{"time":2165,"title":2166,"text":2167},"1600","Gilbert's *De Magnete*","English physician William Gilbert shapes a lodestone into a sphere, calls it a *terrella* (little Earth), and shows that a small compass needle behaves on it just as real compasses behave on Earth — including dipping downward near the poles.",{"id":2169,"type":1524,"title":2170,"problem":2171,"steps":2172},"worked-example-63","Where does the compass north point?","Your teacher says: \"The geographic North Pole is near Earth's magnetic south pole.\" You protest: \"Then my compass needle is lying! Its north end points toward the Arctic, so it must be pointing to a north pole.\" Settle the argument using the attraction rule.",[2173,2174,2175,2176],"Recall the rule: opposite poles attract, like poles repel. A compass needle is a magnet. Its north-seeking end is attracted to whatever pole lies near the geographic North Pole.","If that pole were also a north pole, the needle would be repelled, not attracted. The needle points there voluntarily, so the pole near the Arctic must be a south magnetic pole.","Geographers name the Arctic region \"North\" by the rotation axis, not by magnetism. The magnetic pole sitting there is therefore called the magnetic south pole, even though it is in the north.","Our confusion comes from one word — north — doing two jobs. It names a place on the globe, and it names one type of magnetic pole. This is a labelling problem, not a fault in the compass.",{"id":2178,"type":1485,"variant":1519,"title":2179,"markdown":2180},"callout-64","The 'compass lies' trap","Children — and adults — often think the magnetic pole near the Arctic must be a north pole because the compass needle's north end points to it. The mistake is forgetting that the needle moves because of *force*, not because of shared names. Labels on maps are human conventions; magnetic forces follow the attraction rule. When you hear \"magnetic south pole is near geographic north,\" treat it as a description of where the pole sits, not what it does. The pole's type is defined by its force effect, not its address.",{"id":2182,"type":1472,"markdown":2183},"prose-65","Gilbert's 1600 experiment gave another piece of evidence. He floated his lodestone *terrella* in water and held a small compass near it. The needle not only pointed toward the poles; it also tilted downward, dipping into the surface. Sailors had already noticed that real compasses dip when carried far north or south. Gilbert argued that if a model magnet ball reproduces both direction and dip, the real Earth is probably a magnet too. This was an early example of using a labelled model — the *terrella* — to make a prediction that Earth then satisfied.\n\nModern measurements confirm the picture. The magnetic field lines rise from the southern hemisphere, loop through space, and plunge back in near the Arctic. The field is weak — about 25 to 65 microtesla across India — but it is enough to torque a light compass needle against friction. Spacecraft can map it from above, and geologists read its past direction trapped in ancient volcanic rocks. All of this supports the same conclusion Gilbert reached with his stone ball and hand-held needle.",{"id":2185,"type":1598,"caption":2186,"columns":2187,"rows":2191},"table-66","Poles named by place versus poles named by force",[2188,2189,2190],"Named by","What it means","Example",[2192,2196,2200],[2193,2194,2195],"Geographic place","Position on Earth's rotation axis","Geographic North Pole, Arctic Ocean",[2197,2198,2199],"Magnetic type","How the pole acts on other magnets","Magnetic north pole (currently in southern ocean near Antarctica)",[2201,2202,2203],"Where they sit","The magnetic pole near each geographic region","Magnetic south pole sits near geographic north; magnetic north pole sits near geographic south",{"id":2205,"type":1536,"prompt":2206,"options":2207,"explanation":2216},"prediction-67","You are camping in the Nilgiris. You forget your compass but have a bar magnet and a thread. You suspend the magnet so it can spin freely. Once it stops swinging, which statement best matches what you will observe?",[2208,2210,2212,2214],{"id":1540,"label":2209},"The magnet points in a random direction and stays there.",{"id":1543,"label":2211},"The magnet aligns roughly north-south, with the same end pointing north each time.",{"id":1546,"label":2213},"The magnet points straight down into the ground.",{"id":1549,"label":2215},"The magnet spins forever because no field acts on it.","The correct answer is (b). A freely suspended bar magnet aligns roughly north-south because Earth's magnetic field exerts a torque on it, just as it does on a compass needle. The alignment is not perfectly exact because magnetic north and geographic north differ by a few degrees — the declination — but the pattern is stable. Option (a) would mean no field; (c) describes magnetic dip, which is real but is a tilt, not a vertical plunge at Indian latitudes; (d) ignores the field entirely.",{"id":2218,"type":1485,"variant":1827,"title":2219,"markdown":2220},"callout-68","The bar-magnet-in-Earth model has limits","We often draw Earth as having a giant bar magnet inside, tilted about 11 degrees from the rotation axis. This is a useful labelled model: it predicts field lines, poles, and rough compass direction. But Earth does not contain an actual iron bar. The field is generated by moving liquid iron in the outer core — a dynamo process, not a solid magnet. The model therefore explains direction and dip, but not *how* the field is made. For that we need deeper physics taught in higher classes. Always ask: what does this model predict correctly, and where does it stay silent?",{"id":2222,"type":1476,"title":2223,"eyebrow":2224,"navLabel":2225},"chapter-69","Building an Electromagnet: Coils and Core","Chapter 08","Make and vary",{"id":2227,"type":1472,"markdown":2228},"prose-70","Imagine you could turn a magnet on and off like a light switch. That is exactly what an electromagnet does. Unlike the permanent magnet on your refrigerator door, an electromagnet is a magnet only when electric current flows through a wire coiled around an iron core. The moment you break the circuit, the magnetic effect disappears. This makes electromagnets incredibly useful: railway signals, hospital MRI machines, and the loudspeakers in your phone all rely on this switchable power.\n\nIn this chapter, you will build a simple electromagnet using only an iron nail, insulated copper wire, and a 1.5 V dry cell. You will then investigate a specific question: *Does adding more turns of wire around the same nail make the electromagnet stronger?* To answer this fairly, you will keep everything else unchanged — same nail, same battery, same wire thickness, same paper clips — and change only the number of turns. This is a controlled investigation, the kind engineers at ISRO use when testing how a new motor design behaves under different conditions.\n\nBefore you wind a single turn, pause and predict: if you double the turns, do you double the strength? Let us test your intuition, then build.",{"id":2230,"type":1536,"prompt":2231,"options":2232,"explanation":2241},"prediction-71","You wrap 20 turns of insulated copper wire around an iron nail, connect it to a fresh 1.5 V cell, and lift paper clips. You then rewind with 80 turns on the *same* nail using the *same* wire and battery. How many paper clips do you expect the 80-turn coil to lift compared to the 20-turn coil?",[2233,2235,2237,2239],{"id":1540,"label":2234},"About the same; the battery limits everything.",{"id":1543,"label":2236},"Roughly 4 times as many, because turns multiply directly.",{"id":1546,"label":2238},"More, but less than 4 times maybe 2 to 3 times as many.",{"id":1549,"label":2240},"Fewer, because the battery drains faster with more wire.","Most students initially pick (b), and the prediction direction is right — more turns do strengthen the electromagnet. But the real outcome usually lands closer to (c). With 80 turns the wire is longer, so its resistance increases slightly, the current drops a little, and the battery also drains faster during repeated tests. These hidden variables mean strength rises, but not in perfect proportion to turns. Spotting this gap between ideal prediction and real result is exactly what fair testing is for.",{"id":2243,"type":1491,"title":2244,"items":2245},"steps-72","Building and Testing Your Electromagnet",[2246,2249,2252,2255,2258,2261,2264],{"title":2247,"text":2248},"Gather materials","Iron nail (about 8 cm), 2 m insulated copper wire, 1.5 V dry cell, sandpaper, paper clips, tape, notebook.",{"title":2250,"text":2251},"Prepare the wire ends","Strip 2 cm of insulation from both ends with sandpaper to expose bright copper.",{"title":2253,"text":2254},"Wind 20 turns","Wrap 20 tight, even turns around the middle of the nail, all in the same direction. Leave 15 cm tails at each end.",{"title":2256,"text":2257},"Connect and lift","Touch one bare end to each battery terminal for 10 seconds. Lift slowly and count paper clips held.",{"title":2259,"text":2260},"Repeat and average","Do three trials with 20 turns. Record each count, then average them.",{"title":2262,"text":2263},"Wind 40, 60, 80 turns","Keep the same nail and wire. Rewind carefully, counting aloud. Test each the same way.",{"title":2265,"text":2266},"Watch for battery sag","If later counts drop unexpectedly, the battery may be weakening. Note this as a possible extra variable.",{"id":2268,"type":1598,"caption":2269,"columns":2270,"rows":2276},"table-73","Sample results from a Class 6 investigation ( Mumbai, 2024 )",[2271,2272,2273,2274,2275],"Turns","Trial 1","Trial 2","Trial 3","Average",[2277,2280,2283,2286],[2278,1624,1609,1624,2279],"20","3.3",[2281,1615,1614,1615,2282],"40","6.7",[2284,1918,1620,1918,2285],"60","9.7",[2287,1453,2288,1918,2289],"80","11","11.0",{"id":2291,"type":1485,"variant":1908,"title":2292,"markdown":2293},"callout-74","The Battery Is Part of Your Circuit","A 1.5 V cell is not an endless source. Every time you connect it, chemical reactions inside produce current. After many connections, the voltage falls — a phenomenon called **battery sag**. If your 80-turn test happens after several minutes of testing, a weaker battery can hide the true effect of more turns. The only honest fix: use a fresh cell for each turn count, or at least rest the battery between full sets and record its age in your notes.",{"id":2295,"type":1524,"title":2296,"problem":2297,"steps":2298},"worked-example-75","Analysing Turn Data from a Fair Test","Priya tests 20, 40, 60, and 80 turns with the same nail and a fresh battery for each set. Her averages are 4, 9, 14, and 16 paper clips. She predicts 80 turns should lift double what 40 turns does. Does her evidence fully support this?",[2299,2300,2301,2302,2303],"Check the prediction: double of 9 is 18 paper clips.","Compare to actual: 80 turns lifted 16, not 18.","Calculate the ratio: 16 ÷ 9 = 1.78, not 2.0.","Consider why: the battery was fresh each time, but 80 turns means more total wire length, slightly more resistance, and slightly less current than ideal.","Conclusion: the evidence supports the direction — more turns strengthen the magnet — but challenges the exact doubling prediction. Priya should revise her model to include resistance and current, not just turn count.",{"id":2305,"type":1794,"itemId":2306,"prompt":2307,"check":2308,"hints":2317,"feedback":2321},"practice-76","magnets.p004","Look at Priya's data above. If she tested 100 turns with a slightly tired battery and got 14 clips, what should she conclude about that single result?",{"kind":1798,"options":2309,"correct":2316},[2310,2312,2314],{"id":1540,"label":2311},"100 turns is weaker than 80 turns, so she should reject the whole pattern.",{"id":1543,"label":2313},"The tired battery is a confounding variable; she cannot fairly compare it to the other results.",{"id":1546,"label":2315},"14 clips proves magnets have a maximum strength limit at 80 turns.",[1543],[2318,2319,2320],"Which condition changed this time that did not change before?","Priya's earlier tests all used fresh batteries.","A tired battery means lower current, regardless of turns.",{"correct":2322,"incorrect":2323},"Correct. The battery condition changed, so the 14-clip result confuses turn count with power source weakness. To test fairly, she needs a fresh battery for the 100-turn trial too.","Think again: what else changed in this trial? The battery was tired, unlike before. That means two things changed at once, violating the controlled test idea.",{"id":2325,"type":1472,"markdown":2326},"prose-77","When you coil a current-carrying wire around an iron nail, every loop contributes to a combined magnetic field inside the iron. The iron core itself is a soft magnetic material: its atomic magnets align with the field from the coil but snap back when current stops. This is why an electromagnet is temporary, not permanent. More loops mean more alignment force, up to the point where the iron becomes nearly fully aligned — a state called magnetic saturation. In a school experiment with a small nail and a 1.5 V cell, you are unlikely to reach saturation, but the concept reminds us that no magnet can strengthen forever.\n\nElectromagnets power real devices you use daily. The vibration motor in your parent's smartphone contains a tiny electromagnet pulling a mass back and forth. Loudspeakers rely on an electromagnet pushing and pulling a paper cone to create sound waves. Even the door buzzer in many Indian apartments uses an electromagnet to strike a metal plate. In the next chapter, you will compare electromagnets directly with permanent magnets to understand when each type wins.",{"id":2328,"type":2329,"items":2330},"formulas-78","formulas",[2331],{"expression":2332,"caption":2333},"Strength ∝ (Turns × Current)","A simplified model: electromagnet strength rises with more turns and more current, assuming no saturation.",{"id":2335,"type":1476,"title":2336,"eyebrow":2337,"navLabel":2338},"chapter-79","Electromagnet or Permanent Magnet? A Comparison","Chapter 09","Two kinds compared",{"id":2340,"type":1472,"markdown":2341},"prose-80","Imagine you are designing a sorting yard for a recycling plant in Mumbai. Trucks dump mixed metal waste, and your job is to separate the iron and steel from aluminium, plastic and glass. You could use a permanent magnet hanging from a chain, but once it grabs the scrap, how do you drop it? You would have to pry the metal off with a crowbar, which is slow and dangerous. You could instead use an electromagnet: switch the current on, lift the iron, move it, switch the current off, and the scrap falls cleanly into a bin. The same task, two very different magnets, and the choice changes everything about safety, speed and cost.\n\nIn the last chapter we built a simple electromagnet by wrapping insulated copper wire around an iron nail and passing current from a battery. Now we compare that device with a permanent magnet — the kind you find in a compass, a school badge, or a speaker — to understand when each one wins. The comparison rests on four ideas: control (can you switch it off?), strength (can you change it?), cost (energy and money), and best use (which fits the job).",{"id":2343,"type":1913,"tone":2344,"items":2345},"spec-81","neutral",[2346,2350,2354,2357],{"label":2347,"big":2348,"value":2349},"Permanent magnet","Always on","Needs no battery, circuit, or fuel. Magnetic field is fixed unless physically damaged or heated above its Curie temperature.",{"label":2351,"big":2352,"value":2353},"Electromagnet","Switchable","Needs continuous electric current. Field appears when current flows and disappears when it stops, though an iron core may keep slight residual magnetism.",{"label":2347,"big":2355,"value":2356},"Fixed strength","Strength set by material and shape at factory. Cannot be turned up for a heavy job or down for a delicate one.",{"label":2351,"big":2358,"value":2359},"Adjustable","Strength changes with number of coil turns, current size, and core material. Can be tuned for the exact force needed.",{"id":2361,"type":1524,"title":2362,"problem":2363,"steps":2364},"worked-example-82","The Scrap-Yard Crane: Why Electromagnet Wins","A crane operator in a steel recycling yard must lift a 500 kg pile of iron scrap, move it 20 metres, and release it exactly into a waiting truck. Explain why an electromagnet is used instead of a permanent magnet, and state the one main disadvantage.",[2365,2366,2367,2368],"Step 1: Identify the control problem. A permanent magnet would grip the scrap firmly, but there is no 'off switch'. Releasing half a tonne of metal held by a strong magnet requires mechanical force and risks damaging the magnet or injuring workers.","Step 2: Apply the electromagnet advantage. When the crane reaches the truck, the operator opens the circuit. Current drops to zero, the magnetic field collapses, and the scrap falls by gravity. The release is instant and requires no physical contact.","Step 3: Note the energy cost. The crane must keep the electromagnet powered during the entire lift. If the power fails, the load drops immediately — a safety risk that backup circuits must address. This continuous energy need is the main disadvantage compared with a permanent magnet.","Step 4: Best-use conclusion. Jobs that need 'grab, move, release' cycles favour electromagnets. Jobs that need 'hold forever without power' favour permanent magnets.",{"id":2370,"type":1598,"caption":2371,"columns":2372,"rows":2374},"table-83","Permanent magnet versus electromagnet: a practical comparison",[2373,2347,2351],"Feature",[2375,2379,2383,2387,2391,2395],[2376,2377,2378],"Power needed","None","Continuous electric current",[2380,2381,2382],"Switch off?","No; field is always present","Yes; field stops when current stops",[2384,2385,2386],"Change strength?","Hard; only by damage or heating","Easy; change current or coil turns",[2388,2389,2390],"Make at home?","Hard; needs special alloys","Easy; wire, nail, battery",[2392,2393,2394],"Typical lifetime","Years to decades","Coils and cores last, but overheating or wire breaks are risks",[2396,2397,2398],"Best example","Fridge magnet, compass needle","Scrap-yard crane, door lock",{"id":2400,"type":1476,"title":2401,"eyebrow":2402,"navLabel":2403},"chapter-84","Where Strength Matters: Motors, Speakers, Maglev and Recycling","Chapter 10","Real uses",{"id":2405,"type":1472,"markdown":2406},"prose-85","Think of the last time you rode in an electric train or auto-rickshaw, listened to music through a speaker, or dropped a plastic bottle into a recycling bin. Magnets were working hard in every one of those moments, but they were not all the same kind of magnet. Engineers choose between permanent magnets and electromagnets based on what the job really needs: steady grip or quick release, fixed position or rapid motion, constant field or one that switches on and off thousands of times per second. In this chapter we treat four real devices like experiments. We ask: what condition must the magnetic field satisfy? Then we check whether a permanent bar magnet or an electromagnet can meet that condition. This is the investigative habit you have built across the previous chapters, now applied to machines that shape daily life in India and around the world.",{"id":2408,"type":1485,"variant":2409,"title":2410,"markdown":2411},"callout-86","example","The electric motor in a ceiling fan","A typical Indian ceiling fan contains a motor with copper coils wound around an iron core. When current flows, the core becomes an electromagnet. The field must flip direction every fraction of a second so the rotor keeps spinning. A permanent magnet cannot flip its poles on command, so electromagnets are essential here. The *shape* of the field and the *timing* of the flip matter more than brute strength.",{"id":2413,"type":2414,"title":2415,"prompt":2416,"options":2417},"explorer-87","explorer","Pick a device: what happens if we swap the magnet?","Imagine an engineer replaces the designed magnet with the wrong type. Choose one device to see the failure chain.",[2418,2428,2437],{"id":2419,"label":2420,"chain":2421,"note":2427},"motor","Ceiling fan motor",[2422,2423,2424,2425,2426],"Swap electromagnet for permanent magnet","Poles cannot reverse","Rotor locks in one position","Fan hums but does not spin","Motor overheats and trips","The fan needs timed pole reversals. A permanent magnet gives a fixed north and south. The rotor would align once and stall. Real induction motors use alternating current to create a rotating field without brushes, but the principle of a *changing* field remains essential.",{"id":2429,"label":2430,"chain":2431,"note":2436},"recycling","Scrap-yard crane",[2422,2432,2433,2434,2435],"Lifts steel cans easily","Cannot release at drop zone","Worker must pry each piece loose","Sorting slows to a crawl","This is why scrap yards in industrial areas like Mumbai's Dharavi recycling clusters or Jindal steel plants use giant electromagnets on cranes. The operator lifts a load, moves it, and drops it with a switch. A permanent magnet would create a permanent problem.",{"id":2438,"label":2439,"chain":2440,"note":2446},"maglev","Maglev train",[2441,2442,2443,2444,2445],"Try to levitate with permanent magnets","Gap between track and train changes","Permanent force cannot adjust","Train crashes into track or floats away","No viable control","Japan's SCMaglev and China's Shanghai Transrapid both use superconducting electromagnets for levitation and ordinary electromagnets for propulsion. The control system samples the gap thousands of times per second. Permanent magnets alone would fail the fair test of safe, stable levitation.",{"id":2448,"type":1524,"title":2449,"problem":2450,"steps":2451},"worked-example-88","How loudspeaker designers choose magnet strength and gap shape","A loudspeaker must convert an electrical music signal into sound. A coil of wire sits in a narrow circular gap around a permanent magnet's pole piece. The coil vibrates forward and backward. Why is a strong *permanent* magnet used, and why must the gap be uniform all around?",[2452,2453,2454,2455,2456],"The coil experiences force only where magnetic field lines cross the wire at right angles. The field must be dense and consistent across the gap.","A permanent magnet gives this steady field with no electrical power, so the speaker works even with the amplifier off (though it produces no sound until current flows in the coil).","If the gap is uneven, the coil 'rubs' against one side during loud passages. That produces distortion or destroys the speaker.","An electromagnet here would waste power continuously, add heat, and risk field drift that changes the sound colour. The permanent magnet wins on stability and efficiency.","Real test: measure the magnetic flux density (in millitesla) at ten points around the gap. A fair-test speaker design keeps variation under 5%.",{"id":2458,"type":1485,"variant":1519,"title":2459,"markdown":2460},"callout-89","\"Stronger magnet always means better machine\"","This is a common prediction error. In a maglev train, a magnet *too strong* for the current speed would slam the train into the track. In an MRI scanner at AIIMS Delhi, the field is strong (1.5 to 3 tesla) but also *extremely uniform*; a stronger but uneven field would blur the body image. Engineers optimise strength, shape and control together. Strength is only one variable in the fair test.",{"id":2462,"type":1536,"prompt":2463,"options":2464,"explanation":2471},"prediction-90","A recycling plant in Chennai receives mixed aluminium soft-drink cans and steel food cans on a conveyor. The separator magnet is switched on. What do you predict happens?",[2465,2467,2469],{"id":1540,"label":2466},"Both aluminium and steel cans stick to the magnet",{"id":1543,"label":2468},"Only steel cans stick, and they release when the magnet switches off",{"id":1546,"label":2470},"No cans stick because both metals look silvery","Aluminium is not ferromagnetic. Only steel, which is mostly iron, is attracted to the magnet. The steel cans lift and move to a separate chute. The operator then switches the electromagnet off and the steel drops. This is the separation step in many Indian metal-recycling units. The prediction tests your understanding that magnetic attraction is material-specific, not appearance-specific.",{"id":2473,"type":1476,"title":2474,"eyebrow":2475,"navLabel":2476},"chapter-91","Magnetic Domains: A Model You Can Sketch","Chapter 11","Domain model",{"id":2478,"type":1472,"markdown":2479},"prose-92","After everything you have tested — the paper clips, the heat, the hammer, the iron filings, the electromagnet coil — one quiet question remains: what is actually happening inside the metal? You cannot cut open a steel pin and watch magnetism leak out. You cannot slice iron thin enough to see its atoms line up with a classroom microscope. Yet scientists needed a way to explain why stroking works, why heating undoes it, why soft iron and hard steel behave so differently. Their answer is not a photograph; it is a model called **magnetic domains**.\n\nA **model** is a simplified story or picture that explains real behaviour without copying every detail. The domain model says this: inside iron, nickel, cobalt and some steels, atoms group into small regions called **domains**, each region acting like a tiny magnet with its own north pole and south pole. When the bar is unmagnetised, these domains point in random directions, so their effects cancel out. When the bar is magnetised, the domains line up, and their tiny fields add together into one strong field you can feel. This chapter shows how to sketch that model, how to use it to explain your experiments, and why you must always remember it is a tool, not a photograph.",{"id":2481,"type":1491,"title":2482,"items":2483},"steps-93","How to sketch the domain model in three stages",[2484,2488,2492],{"title":2485,"tag":2486,"text":2487},"Draw the unmagnetised bar","Stage 1","Draw a rectangle for the iron bar. Inside it, draw 6–8 small arrows pointing in random directions — up, down, left, right, diagonal. Label each arrow \"domain.\" Add a note: \"No overall N or S; fields cancel.\"",{"title":2489,"tag":2490,"text":2491},"Show partial magnetisation","Stage 2","Draw a second bar. Show a strong magnet nearby, or a stroking arrow along the bar. Now draw most arrows pointing right, but leave 1–2 still tilted. Label: \"Domains aligning; weak overall magnetism.\"",{"title":2493,"tag":2494,"text":2495},"Show full magnetisation","Stage 3","Draw a third bar with all arrows pointing the same direction, right to left. Label one end \"N\" and the other \"S.\" Add: \"Aligned domains; strong external field.\"",{"id":2497,"type":1472,"markdown":2498},"prose-94","Now run your experiments backward through the model. When you stroked the steel needle with a bar magnet, you were nudging domains to swivel and stay aligned. The more strokes, the more domains joined the crowd pointing one way. That is why the needle could then lift paper clips — enough tiny fields added up to matter. When you heated the same needle over a candle, the heat made atoms vibrate faster. The vibration jostled domains out of alignment; they fell back to random directions. The model predicts what you saw: heat weakens magnetism because it scrambles order into disorder.\n\nDropping or hammering does something similar. A sharp blow sends a shock wave through the metal. Domains that were neatly lined up get knocked sideways. The model also explains why soft iron makes a good electromagnet core but a poor permanent magnet. In soft iron, domains swivel easily when the coil is switched on, so the field rises fast. But they also swivel back easily when the current stops, so the iron loses magnetism almost immediately. Hard steel is the opposite: its domains resist change. They need strong force to align, and once aligned they stay that way. That resistance makes steel useful for permanent refrigerator magnets, but useless as a relay core that must switch on and off hundreds of times a minute.",{"id":2500,"type":1598,"caption":2501,"columns":2502,"rows":2506},"table-95","Soft iron versus hard steel in the domain model",[2503,2504,2505],"Property","Soft iron","Hard steel",[2507,2511,2515,2519,2523],[2508,2509,2510],"Domains move...","easily","only under strong force",[2512,2513,2514],"Magnetise with coil?","Yes, quickly","Slowly or not at all",[2516,2517,2518],"Lose magnetism when current stops?","Almost immediately","Barely",[2520,2521,2522],"Best use","Electromagnet cores, relays","Permanent magnets, compass needles",[2524,2525,2526],"Your home example","Iron nail in a coil","Fridge magnet or door latch magnet",{"id":2528,"type":1485,"variant":1827,"title":2529,"markdown":2530},"callout-96","No one has photographed a single domain with school tools","The domain model is powerful, but it is a **human-built simplification**, not a snapshot from a camera. Scientists infer domains from indirect evidence — how crystals scatter X-rays, how electron beams bend near metal surfaces, how computer simulations behave. A single magnetic domain is smaller than a grain of sand by a factor of millions. Your classroom microscope, even the best light microscope, cannot resolve anything close to that scale. So when you sketch arrows inside a bar, you are drawing a useful story, not an eyewitness report. Good scientists treat the model as a torch that lights the path, not as the path itself.",{"id":2532,"type":1524,"title":2533,"problem":2534,"steps":2535},"worked-example-97","Explaining stroking with the domain model","A student strokes an iron nail from end to end with the north pole of a bar magnet, always moving in the same direction. After thirty strokes the nail lifts three paper clips. Use the domain model to explain: (a) why the nail becomes a magnet, and (b) why dragging the magnet back and forth randomly produces little or no effect.",[2536,2537,2538,2539],"Imagine the unmagnetised nail: domains point every which way, like a crowd facing all directions. Their tiny magnetic fields cancel; the nail cannot lift anything.","Each stroke pushes domains near the bar magnet's pole to swivel and align with the magnet's field direction. Because the student always strokes the same way, domains get a repeated nudge in one direction.","After many strokes most domains point the same way along the nail. Their fields add up. One end of the nail behaves as a north pole, the other as a south pole, and the nail lifts clips.","If the student scrubs back and forth randomly, domains are nudged left, then right, then left again. They never settle into a lasting majority direction. The crowd stays mixed; fields still cancel. The nail remains weak or unmagnetised.",{"id":2541,"type":1536,"prompt":2542,"options":2543,"explanation":2552},"prediction-98","You have two identical steel needles. You magnetise both by stroking fifty times. Then you place needle A in a freezer overnight and needle B in hot sunlight for three hours. Using the domain model, predict which needle lifts more paper clips the next morning.",[2544,2546,2548,2550],{"id":1540,"label":2545},"Needle A (frozen) lifts more; cold helps domains stay aligned.",{"id":1543,"label":2547},"Needle B (heated) lifts more; heat excites domains and strengthens them.",{"id":1546,"label":2549},"Both lift the same; temperature does not affect steel magnetism.",{"id":1549,"label":2551},"Neither lifts any; both needles lose all magnetism quickly.","The correct prediction is **A**. The domain model says that heat makes atoms vibrate and jostle domains out of alignment. Cold reduces this jostling, so aligned domains stay aligned longer. Needle B's heating period gives domains more chance to randomise, weakening the overall field. Needle A stays stronger. This matches your earlier fair-test investigation with heat and magnets, now explained by a mechanism you cannot see directly.",{"id":2554,"type":1794,"itemId":2555,"prompt":2556,"check":2557,"hints":2568,"feedback":2572},"practice-99","magnets.p005","A relay in a railway signal uses a soft-iron core inside a copper coil. When current flows, the relay must pull a switch closed within a fraction of a second. When current stops, the switch must spring open within a fraction of a second. Explain why soft iron is chosen, not hard steel, using the domain model.",{"kind":1798,"options":2558,"correct":2567},[2559,2561,2563,2565],{"id":1540,"label":2560},"Soft iron's domains align quickly and return quickly; hard steel's domains resist both changes.",{"id":1543,"label":2562},"Soft iron is cheaper to buy at Indian railway workshops.",{"id":1546,"label":2564},"Hard steel would melt from the current in the coil.",{"id":1549,"label":2566},"Soft iron has no domains, so it cannot stay magnetised.",[1540],[2569,2570,2571],"Think about what 'soft' means in the domain model, not in everyday language.","Would a signal that stays stuck 'on' after the power fails be safe or dangerous?","Does the core need to keep magnetism after the switch turns off?",{"correct":2573,"incorrect":2574},"Correct. Soft iron's domains swivel easily, so the relay responds fast to both 'on' and 'off' commands. Hard steel would stay magnetised, keeping the switch stuck closed even when the power fails — a safety risk.","Revisit the table comparing soft iron and hard steel. The key difference is how easily domains change direction. Cost and melting are not the deciding factors here, and soft iron definitely does have domains.",{"id":2576,"type":1476,"title":2577,"eyebrow":2578,"navLabel":2579},"chapter-100","Check Yourself, and What Comes Next","Chapter 12","Quiz and bridge",{"id":2581,"type":1472,"markdown":2582},"prose-101","You have now carried out investigations about attraction and repulsion, tested which materials stick, weakened magnets on purpose, mapped invisible fields with iron filings, built an electromagnet from wire and a nail, and used the domain model to explain why some materials become magnets while others do not. Along the way you met the compass, maglev trains, recycling yards, and the giant magnet that is Earth itself. This closing chapter is your chance to check what has stuck — and to peek at where the next depth of study will take you. Grab a pencil, read each question carefully, and treat every option as a small investigation of its own.",{"id":2584,"type":2585,"title":2586,"questions":2587},"quiz-102","quiz","Magnet Investigation Lab — Final Check",[2588,2601,2614,2625,2638,2651,2664],{"itemId":2589,"prompt":2590,"options":2591,"correct":1543,"why":2600},"magnets.q006","In a fair test to find which magnet shape holds the most paper clips, what must stay the same for every trial?",[2592,2594,2596,2598],{"id":1540,"label":2593},"The number of paper clips available in the box",{"id":1543,"label":2595},"The size and material of each paper clip, and how they are added",{"id":1546,"label":2597},"The colour of the magnet",{"id":1549,"label":2599},"The humidity in the room, even if it changes","A fair test changes only the independent variable (magnet shape) and keeps controlled variables identical. Paper clip size, material, and adding method must stay the same so that any difference in count is caused by shape, not by the clips themselves. Curiosity: Textbook of Science for Grade 6, Chapter 4 (Exploring Magnets) discusses fair-test design in investigation activities.",{"itemId":2602,"prompt":2603,"options":2604,"correct":1543,"why":2613},"magnets.q007","A student heats a bar magnet in a pan over a flame, then tries to pick up iron filings. Fewer filings stick than before. What is the most likely reason?",[2605,2607,2609,2611],{"id":1540,"label":2606},"The filings melted and became plastic",{"id":1543,"label":2608},"Heat made the magnetic domains lose their common alignment",{"id":1546,"label":2610},"The magnet's mass decreased",{"id":1549,"label":2612},"Iron filings are always non-magnetic above 30 °C","Heating adds energy that randomises the magnetic domains, destroying the organised alignment that produces the overall field. The domains model — treated as a simplified model in this lesson — explains why heat weakens or destroys magnetism.",{"itemId":2615,"prompt":2616,"options":2617,"correct":1546,"why":2624},"magnets.q008","Which of these materials is strongly attracted to a permanent magnet?",[2618,2620,2622,2623],{"id":1540,"label":2619},"Aluminium soft-drink can",{"id":1543,"label":2621},"Copper electrical wire",{"id":1546,"label":1727},{"id":1549,"label":1765},"Iron is a ferromagnetic material. Aluminium, copper and wood are not attracted to magnets. Curiosity: Textbook of Science for Grade 6, Chapter 4 (Exploring Magnets) classifies iron, nickel and cobalt as magnetic materials.",{"itemId":2626,"prompt":2627,"options":2628,"correct":1543,"why":2637},"magnets.q009","You wrap insulated copper wire around an iron nail and connect it to a 1.5 V cell. What happens?",[2629,2631,2633,2635],{"id":1540,"label":2630},"Nothing, because nails cannot become magnets",{"id":1543,"label":2632},"The nail becomes a temporary magnet while current flows",{"id":1546,"label":2634},"The wire melts instantly",{"id":1549,"label":2636},"The cell charges the nail permanently","Electric current through a coil creates a magnetic field. The iron core strengthens this field. When current stops, the nail usually loses most of its magnetism — an electromagnet, not a permanent magnet.",{"itemId":2639,"prompt":2640,"options":2641,"correct":1543,"why":2650},"magnets.q010","Why does a compass needle point north?",[2642,2644,2646,2648],{"id":1540,"label":2643},"The needle is attracted to the North Star",{"id":1543,"label":2645},"Earth behaves like a giant magnet with a magnetic field",{"id":1546,"label":2647},"Wind in the upper atmosphere pushes the needle",{"id":1549,"label":2649},"The compass contains a tiny battery","Earth has a magnetic field, generated by moving material in its outer core. A compass needle, itself a small magnet, aligns with this field. The geographic North Pole is near the magnetic south pole — a nuance worth remembering.",{"itemId":2652,"prompt":2653,"options":2654,"correct":1543,"why":2663},"magnets.q011","A student says: \"My compass needle points to the right side of my bar magnet, so that side must be the north pole.\" Is this reasoning always correct?",[2655,2657,2659,2661],{"id":1540,"label":2656},"Yes, because the needle always points to north poles",{"id":1543,"label":2658},"No, because the compass could be repelling from the south pole if the needle flips",{"id":1546,"label":2660},"No, because compasses only work outdoors",{"id":1549,"label":2662},"Yes, because colours on the magnet show the poles","A compass needle's north-seeking end points away from a magnetic north pole (like poles repel) and toward a magnetic south pole. The student must observe attraction versus repulsion, not just the direction of pointing, to identify poles reliably. This is a common mix-up addressed earlier in the lesson.",{"itemId":2665,"prompt":2666,"options":2667,"correct":1543,"why":2676},"magnets.q012","Using the domain model, explain why repeatedly dropping a magnet on a hard floor makes it weaker.",[2668,2670,2672,2674],{"id":1540,"label":2669},"Domains break into smaller pieces like shattered glass",{"id":1543,"label":2671},"Physical shock gives energy that randomises domain alignment, so their fields no longer add up",{"id":1546,"label":2673},"Gravity reverses the magnetic field direction",{"id":1549,"label":2675},"The magnet loses iron atoms with each bounce","The domain model describes regions where atomic magnets line up. Dropping or hammering disturbs this alignment. The model simplifies real crystal behaviour but correctly predicts that disorder weakens the overall field.",{"id":2678,"type":1485,"variant":1908,"title":2679,"markdown":2680},"callout-103","A common slip in electromagnet planning","When students plan to test 'how many coils makes the strongest electromagnet,' some change the wire length and the number of coils together. This is not a fair test. If you double the coils by adding twice as much wire, you also change resistance and how the coils pack together. To test coil number alone, keep the same wire length and thickness, but wind it into different numbers of turns on an identical iron core each time. Control your variables so the claim is about turns, not about total wire.",{"id":2682,"type":1524,"title":2683,"problem":2684,"steps":2685},"worked-example-104","Designing a fair test for electromagnet strength","Priya wants to find whether an iron nail or a steel bolt makes a stronger electromagnet core. She has two identical coils of insulated copper wire, one 1.5 V cell, and a box of identical steel paper clips. How should she set up a fair test?",[2686,2687,2688,2689,2690,2691],"Keep the number of turns, wire thickness, cell voltage, and the way clips are counted exactly the same for both cores.","Wrap one coil onto the iron nail and the other onto the steel bolt, making sure the turns are as similar as possible in tightness and position.","Connect each electromagnet to the same type of cell, one at a time, and count how many paper clips hang in a chain from the end.","Repeat each test three times and calculate the average, because single measurements can be affected by how a clip was placed.","Compare the averages. The core with the higher average clip count is the stronger electromagnet under these conditions.","Record that iron concentrates magnetic field more strongly than steel for temporary electromagnets, though steel may keep some magnetism after the current stops.",{"id":2693,"type":1472,"markdown":2694},"prose-105","Where does study go after 'investigate'? The next depth — 'extend' — treats magnetic field direction as a precise mathematical idea. You will learn that field at any point has both strength and direction, making it a vector quantity. For electromagnets, the right-hand grip rule lets you predict the north pole from the way current curls through the coil, without guessing. Most excitingly, you will design a simple DC motor: here the secret is not just the magnetic field, but the timing of field switching, so the spinning armature is pushed around continuously rather than snapping to one position and stopping. The electromagnet you built with a nail and wire is the ancestor of every motor in a train, fan, or washing machine — and at 'extend' depth you will see exactly why the switching must be timed so carefully.",{"id":2696,"type":1659,"title":2697,"points":2698},"summary-106","What to carry forward from this lesson",[2699,2700,2701,2702,2703,2704,2705,2706,2707,2708,2709,2710],"A magnet attracts iron, nickel, cobalt and some steels; it does not attract most other common materials.","Every pole of a magnet is either north or south: like poles repel, unlike poles attract.","Magnetic field is invisible, but iron filings and compass needles give reproducible evidence of its shape and direction.","A fair test changes only one variable at a time and repeats measurements to reduce uncertainty.","Heat, dropping and hammering weaken permanent magnets by disturbing magnetic domain alignment.","Stroking an iron object with a magnet can magnetise it temporarily or permanently, depending on the material.","Earth has a magnetic field; a compass needle aligns with this field and therefore points approximately north.","An electromagnet needs electric current through a coil and is strengthened by an iron core; it can be switched on and off.","Permanent magnets keep their magnetism without power; electromagnets offer control but usually need continuous current.","Magnetic domains are a useful model, not tiny physical switches, for explaining why some materials magnetise and others do not.","Magnets appear in motors, speakers, MRI scanners, maglev trains and recycling separators because they produce force without contact.","No magnet attracts non-magnetic materials like wood, plastic, copper or aluminium under ordinary conditions.",{"id":2712,"type":2713,"title":2714,"terms":2715},"glossary-107","glossary","Key terms from this lesson",[2716,2720,2724,2728,2732,2736,2740,2744,2747,2751,2755,2758,2761],{"term":2717,"meaning":2718,"example":2719},"Magnet","An object that produces a magnetic field and can attract iron, nickel, cobalt and certain steels.","A bar magnet from a school laboratory.",{"term":2721,"meaning":2722,"example":2723},"Magnetic pole","A region on a magnet where the magnetic effect is strongest; every magnet has at least a north pole and a south pole.","The red-painted end of a bar magnet is often labelled north.",{"term":2725,"meaning":2726,"example":2727},"Attraction","The pulling force between opposite magnetic poles or between a magnet and a magnetic material.","A magnet pulling an iron nail across a table.",{"term":2729,"meaning":2730,"example":2731},"Repulsion","The pushing force between like magnetic poles (north-north or south-south).","Two north poles facing each other slide apart.",{"term":2733,"meaning":2734,"example":2735},"Magnetic field","The region around a magnet where magnetic forces act on other magnets or magnetic materials.","The pattern shown by iron filings scattered around a bar magnet.",{"term":2737,"meaning":2738,"example":2739},"Ferromagnetic material","A material that is strongly attracted to magnets and can be magnetised, such as iron, nickel or cobalt.","An iron nail or a steel paper clip.",{"term":2741,"meaning":2742,"example":2743},"Non-magnetic material","A material not attracted to magnets and not easily magnetised.","Wood, plastic, copper or aluminium.",{"term":2351,"meaning":2745,"example":2746},"A magnet made by passing electric current through a coil of wire, usually with an iron core.","A nail wrapped with copper wire connected to a cell.",{"term":2748,"meaning":2749,"example":2750},"Magnetic domain","A small region within a ferromagnetic material where atomic magnets are aligned; a model used to explain magnetisation and demagnetisation.","In an unmagnetised nail, domains point randomly; in a magnetised nail, many domains point the same way.",{"term":2752,"meaning":2753,"example":2754},"Fair test","An investigation in which only the variable being tested is changed, while all other conditions are kept the same.","Testing magnet strength with identical paper clips each time.",{"term":1580,"meaning":2756,"example":2757},"A factor that is kept constant in an experiment so it does not affect the outcome.","Using the same size paper clips when comparing different magnets.",{"term":1576,"meaning":2759,"example":2760},"The factor deliberately changed by the investigator to test its effect.","The number of turns in the coil when testing electromagnet strength.",{"term":1590,"meaning":2762,"example":2763},"The factor that is measured to see how it responds to changes in the independent variable.","The number of paper clips lifted by the electromagnet.",{"id":2765,"type":2766,"sourceIds":2767},"sources-108","sources",[2768,2769],"magnets-ncert-curiosity-6-ch4","angles-wiki-degree",[2768,2769],"needs_review",{"generatedBy":2773,"notes":2774},"claude-code","generated from work item wi-61bfa1ee (12 chapters)","1eda4fb4f8a790c499c73c4840dc4a23ef3b23d93219894c43ce8b5e8c350fa3",{},{"state":6,"reviewer":2778,"selfReview":2779,"reviewedAt":2780,"method":806},"curator",false,"2026-09-21T04:52:13.354622+00:00","generation-19f885ad-fe89-48be-9528-20ae7eee520b",[2783,2791],{"id":2769,"title":2784,"publisher":2785,"url":2786,"kind":2787,"accessed":2788,"usage":2789,"verification":2790},"Degree (angle)","Wikipedia","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FDegree_(angle)","reference","2026-09-20","Supports the history of dividing a full turn into 360 parts (Babylonian sexagesimal astronomy, closeness to the days in a year, many divisors of 360) and minutes and seconds of arc.","machine_checked",{"id":2768,"title":2792,"publisher":2793,"url":2794,"kind":2795,"accessed":2796,"usage":2797,"verification":2790},"Curiosity: Textbook of Science for Grade 6, Chapter 4 (Exploring Magnets)","NCERT","https:\u002F\u002Fncert.nic.in\u002Ftextbook\u002Fpdf\u002Ffecu104.pdf","educational","2026-09-21","Magnets and magnetic materials: which objects a magnet attracts (iron, nickel, cobalt) and which it does not; poles of a bar magnet; attraction and repulsion between poles; the magnetic compass and finding directions; keeping magnets safe. NCERT Class 6 Science (Curiosity), Reprint 2026-27."]