[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"content-index":3,"content-layer:magnets:understand":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":2535,"dependencyHashes":2536,"approval":2537,"releaseId":2541,"sources":2542},{"schemaVersion":44,"conceptId":789,"locale":1436,"depth":150,"revision":44,"title":808,"subtitle":809,"summary":810,"objectives":1437,"estimatedMinutes":805,"plate":1443,"blocks":1469,"sourceIds":2530,"reviewStatus":2531,"authoring":2532},"en",[1438,1439,1440,1441,1442],"Learners can explain why only certain materials (iron, nickel, cobalt and steel) stick to magnets while others (wood, plastic, copper, aluminium) do not.","Learners can describe how a material's atomic structure—specifically the alignment of magnetic domains—determines whether it is magnetic or non-magnetic.","Learners can distinguish between temporary and permanent magnets based on how easily their magnetic domains become disordered.","Learners can identify common misconceptions, such as believing all metals are magnetic or that magnetism works through all materials equally.","Learners can predict and justify whether an unfamiliar material would likely be attracted to a magnet using what they know about its composition.",{"title":1444,"rows":1445},"Understand",[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","11",{"label":1455,"value":1456},"Prior knowledge","Poles attract and repel; magnets have two poles",{"label":1458,"value":1459},"Units used","No new units; terms defined in Hindi and English",{"label":1461,"value":1462},"NCERT chapter","Grade 6, Chapter 4: Exploring Magnets",{"label":1464,"value":1465},"Time to read","About 35 minutes",{"label":1467,"value":1468},"Try at home","Iron filings, compass, steel spoon, copper wire, bar magnet",[1470,1474,1480,1483,1501,1507,1510,1521,1524,1529,1534,1537,1540,1551,1579,1590,1595,1598,1615,1635,1640,1643,1653,1664,1684,1689,1692,1697,1721,1729,1762,1779,1801,1804,1809,1812,1816,1819,1829,1833,1853,1862,1867,1870,1890,1894,1897,1907,1911,1939,1952,1956,1961,1964,1985,1988,1992,2001,2016,2054,2057,2062,2065,2069,2085,2089,2100,2122,2125,2128,2133,2136,2140,2162,2173,2177,2180,2185,2207,2212,2215,2243,2246,2257,2279,2283,2286,2291,2294,2401,2432,2435,2440,2450,2465,2524],{"id":1471,"type":1472,"markdown":1473},"prose-1","prose","Push a magnet toward an iron nail and it leaps into your hand; do the same with a copper coin and nothing happens. Most children learn this rule early — iron sticks, wood does not — yet the *why* stays hidden. This lesson opens that hidden world.\n\nWe will meet the tiny atomic teams called **magnetic domains**, see how their alignment creates attraction or emptiness, learn why steel stays magnetic while soft iron forgets quickly, and practise spotting the mix-ups that even adults repeat. By the end you can predict whether an unknown metal will stick, and you will understand what magnets truly cannot do.",{"id":1475,"type":1476,"title":1477,"eyebrow":1478,"navLabel":1479},"chapter-2","chapter","Two Surprises at the Breakfast Table","Chapter 01","Morning surprises",{"id":1481,"type":1472,"markdown":1482},"prose-3","Imagine you are setting the breakfast table on a rainy monsoon morning in Mumbai. Your mother asks you to hang a steel spoon on the fridge door with a small souvenir magnet from Goa. The spoon clicks into place and hangs there, swaying gently whenever someone opens the fridge for the milk. Later, she asks you to do the same with an aluminium kadai lid — the shiny, silver-coloured cover from a cooking pot. You press the magnet against it. Nothing. The lid slides down and clatters onto the floor.\n\nBoth objects are metals. Both feel cold to the touch. Both came from a kitchen shop. Yet one sticks and the other does not. If you walk into a classroom and ask thirty students, \"Do all metals stick to a magnet?\" more than half will probably say yes. They have seen metal keys stick, metal coins stick, metal spoons stick. The aluminium lid feels like a betrayal of that rule.\n\nThis chapter is about that surprise. The surprise is not that the spoon sticks. The surprise is that your everyday guess — \"metal means magnetic\" — fails so quickly. Science often begins when a habit of guessing runs into a solid wall. The wall here is the inside of the aluminium, and what we will call the magnetic family: a small club of materials with a special atomic arrangement that lets them respond to a magnet. Iron is in that club. Nickel and cobalt are too. Copper and aluminium, despite being excellent metals for wires and cooking, are not invited.\n\nBefore we look at why this happens, let us first see how reliable your own guesses are.",{"id":1484,"type":1485,"prompt":1486,"options":1487,"explanation":1500},"prediction-4","prediction","You have four objects on a kitchen shelf: a steel spoon, an aluminium foil sheet, a copper wire, and a cast-iron tawa. You hold a strong bar magnet near each one, but not touching. Which objects will move toward the magnet or stick to it?",[1488,1491,1494,1497],{"id":1489,"label":1490},"all","All four will stick or move",{"id":1492,"label":1493},"steel-iron","Only the steel spoon and the cast-iron tawa",{"id":1495,"label":1496},"aluminium-copper","Only the aluminium foil and copper wire",{"id":1498,"label":1499},"steel-only","Only the steel spoon","The correct choice is 'Only the steel spoon and the cast-iron tawa.' Steel is mostly iron mixed with a little carbon; cast iron is almost pure iron. Both belong to the magnetic family. Aluminium and copper are metals, but they are outside that family. A magnet will not pull them at all. This is the exact surprise from the breakfast table: 'metal' and 'magnetic' are not the same word. Keep this result in mind — we will explain the atomic reason in later chapters.",{"id":1502,"type":1503,"variant":1504,"title":1505,"markdown":1506},"callout-5","callout","misconception","The Shiny-Metal Trap","**The most common wrong idea:** If something looks like a metal — shiny, hard, cold — it must stick to a magnet.\n\nThis guess works for iron and steel, so our brains overgeneralise. But copper wiring in your home, aluminium window frames, and brass door handles are all metals that a magnet ignores. The colour and shine reveal only the surface. Whether a magnet pulls depends on what kind of atoms are packed inside, not on how polished the surface looks.",{"id":1508,"type":1472,"markdown":1509},"prose-6","Why does this mistake survive so long? Partly because our first encounters with magnets are so staged. Toy magnets often come with iron paper clips, iron nails, and iron filings. The kit is rigged to succeed. A child rarely receives a magnet alongside an aluminium ruler or a copper coin. So the pattern \"magnet grabs metal\" gets reinforced dozens of times before the first counter-example appears.\n\nAnother reason is language. In Hindi and in English, we say \"dhaatu\" or \"metal\" as one big group. We do not have a casual word for \"the three magnetic metals plus their close mixtures.\" Scientists use the term **ferromagnetic materials** (from Latin *ferrum*, meaning iron) for this smaller club. We will meet that word properly in Chapter 3. For now, just remember that the magnetic family is a sub-group inside the larger city of metals, not the whole city.\n\nLet us make this concrete with a table you could actually test at home with a refrigerator magnet and a kitchen scale. The table lists common household items, what they are made of, and what a magnet does to them.",{"id":1511,"type":1512,"title":1513,"problem":1514,"steps":1515},"worked-example-7","worked_example","Testing an unknown metal key","Your grandfather gives you a heavy, dark-grey key. You suspect it might be iron, but it could also be a zinc alloy coated with dark paint. You have only a strong bar magnet and your eyes. How do you decide fairly?",[1516,1517,1518,1519,1520],"Wipe the key clean and dry so water or grease does not interfere.","Hold the magnet near the key without touching it. Does the key move toward the magnet? If yes, it is likely magnetic.","If there is no movement, touch the magnet to the key. Does it stick with any force at all?","If it still does not stick, try a different spot on the key — some keys have iron inside but a brass coating on the cut edge.","If no spot sticks, the key is probably zinc, brass, or another non-magnetic alloy. Record your result before guessing again.",{"id":1522,"type":697,"prompt":1523},"reflection-8","Look around the room you are in right now. List three objects you think are made of metal. For each one, ask yourself: do I have any evidence that a magnet would stick, or am I assuming it because the object is shiny and hard? What single test would settle the question?",{"id":1525,"type":1503,"variant":1526,"title":1527,"markdown":1528},"callout-9","observation","From Outside to Inside","The breakfast-table puzzle forces us to look inward. A magnet does not read the label on a kadai lid. It does not care about price, weight, or brand. It responds to a hidden property of the atoms inside the material. \n\nIn the next chapter we will name the members of the magnetic family precisely. Then in Chapter 3 we will open the atom itself and find the surprising fact: even inside iron, magnetism is not automatic. It appears only when billions of tiny atomic magnets line up like soldiers on a parade ground. The kadai lid fails because its soldiers point in random directions. The steel spoon succeeds because someone — perhaps a factory magnet during manufacturing — has already lined them up.",{"id":1530,"type":1476,"title":1531,"eyebrow":1532,"navLabel":1533},"chapter-10","The Magnetic Family: Iron, Nickel, Cobalt and Their Friends","Chapter 02","The magnetic family",{"id":1535,"type":1472,"markdown":1536},"prose-11","Walk into any kitchen in India and you will find metals everywhere: iron tawa for crisping rotis, aluminium foil covering yesterday's dal, copper-bottomed pans for even heat, and maybe a steel spoon stirring chai. But bring a magnet close, and something strange happens. The iron tawa leaps to meet it. The steel spoon comes too, though a little less eagerly. The aluminium foil? It falls back, indifferent. The copper pan? Not a twitch. Why does the magnet choose its friends so carefully?\n\nThe answer is not about weight, shine, or price. A heavy brass tap and a light iron nail look equally metallic, yet the magnet ignores the tap and hugs the nail. To understand this, we need to meet the magnetic family — a very small club of elements that naturally feel the pull of a magnet at ordinary temperatures.",{"id":1538,"type":1472,"markdown":1539},"prose-12","Notice how short the 'Yes' list is. Nickel and cobalt are the iron element's only pure-element companions in the magnetic club. Cobalt is so rare in everyday objects that most people never handle it except inside batteries or special alloys. Nickel appears in some older coins and in stainless steel. Iron, of course, is everywhere — from construction rods to your mother's iron press.\n\nBut what about steel? Steel deserves its own mention because it creates endless confusion. Steel is not an element. It is an alloy: mostly iron mixed with small amounts of carbon and, in stainless varieties, chromium and nickel. Because iron dominates, steel keeps the magnetic invitation. However, the extra ingredients change the personality of the metal. Soft iron — the kind in nails and transformer cores — gives up its magnetism the moment the external magnet is removed. Hard steel, as in a good knife or a permanent magnet itself, holds onto magnetism for years. The same kitchen magnet that clings fiercely to a steel fridge may slide off an aluminium window frame without a whisper of attraction.\n\nHere is where many students stumble. They learn that 'metals' conduct electricity, and they know magnets stick to metals, so they assume all metals must stick to magnets. This is a trap. Conductivity and magnetism are separate talents. Copper wires carry electricity brilliantly but laugh at magnets. Gold jewellery gleams and conducts, yet a magnet treats it like wood.",{"id":1541,"type":1512,"title":1542,"problem":1543,"steps":1544},"worked-example-13","Sorting scrap at a Mumbai recycling unit","A Mumbai recycling yard receives a mixed pile of copper wires, aluminium window frames, iron rods, and steel pipes. Workers must separate the ferromagnetic metals quickly using a large electromagnet on a crane. The supervisor notices one steel pipe and one iron rod are identical in length and diameter. Both stick to the magnet. How should the workers tell them apart without chemical tests?",[1545,1546,1547,1548,1549,1550],"Recall that iron is 'soft' ferromagnetic: it magnetises strongly while the external field is present, but loses nearly all magnetism when the magnet is removed.","Steel, especially hard carbon steel, is 'hard' ferromagnetic: it retains some magnetism after the external field is removed.","Lift both objects with the electromagnet, then switch the electromagnet off and watch what happens.","The iron rod will drop almost immediately — it was only temporarily magnetic.","The steel pipe will cling to the electromagnet for a moment longer, or may even pull toward any nearby iron, betraying its retained magnetism.","This simple behaviour test separates them: temporary versus retained magnetism, caused by the same underlying domain structure arranged differently.",{"id":1552,"type":1553,"itemId":1554,"prompt":1555,"check":1556,"hints":1572,"feedback":1576},"practice-14","practice","magnets.p001","Rani finds four metal strips in her father's workshop: copper, aluminium, iron, and steel. She has only a bar magnet. She knows copper and aluminium will not stick. How can she tell the iron strip from the steel strip using only the magnet and her eyes?",{"kind":1557,"options":1558,"correct":1571},"choice",[1559,1562,1565,1568],{"id":1560,"label":1561},"a","Look for rust; only iron rusts, steel never does",{"id":1563,"label":1564},"b","Both iron and steel stick, but iron loses magnetism faster when the bar is removed",{"id":1566,"label":1567},"c","Steel is always heavier than iron, so she should weigh them",{"id":1569,"label":1570},"d","Hit them with a hammer; only iron makes a ringing sound",[1563],[1573,1574,1575],"Think about what happens after the magnet is taken away, not just during contact.","Remember the difference between soft and hard magnetic materials.","Rusting and weight depend on conditions and exact composition, not just the iron\u002Fsteel distinction.",{"correct":1577,"incorrect":1578},"Correct. Both iron and steel are ferromagnetic, so both stick. The difference is that soft iron loses its induced magnetism almost immediately, while hard steel retains some. Rani can stroke each strip with the magnet, lift it, then remove the magnet and see which stays magnetic longer.","Not quite. Rust depends on environment and steel type; weight varies with size; sound tests are unreliable. The reliable difference is magnetic retention: iron loses magnetism quickly, steel keeps some.",{"id":1580,"type":1581,"title":1582,"points":1583},"summary-15","summary","The magnetic family in brief",[1584,1585,1586,1587,1588,1589],"Only three pure elements are naturally ferromagnetic at room temperature: iron, nickel, and cobalt.","Steel is magnetic because it is mostly iron, but its extra ingredients change how strongly and how permanently it magnetises.","Common metals like copper, aluminium, brass, gold, and silver are not ferromagnetic, even though they are metals.","Magnetism and electrical conductivity are independent properties; a metal can be excellent at one and terrible at the other.","Soft iron gains and loses magnetism easily; hard steel retains magnetism — a difference that has practical uses in industry.","Always test with a real magnet rather than assuming a metal is or is not magnetic based on appearance alone.",{"id":1591,"type":1476,"title":1592,"eyebrow":1593,"navLabel":1594},"chapter-16","Domains: The Invisible Teams Inside Iron","Chapter 03","Tiny teams",{"id":1596,"type":1472,"markdown":1597},"prose-17","Walk into any scrap yard in India and you will see a giant electromagnet lifting a car, dropping it, then lifting it again. The car was not a magnet a moment ago; it became one in seconds. How can a plain piece of iron suddenly pull, then stop? The answer is not magic. It is something happening deep inside the metal, at a scale far too small to see even with an ordinary microscope. Scientists picture iron as being full of invisible teams called **magnetic domains**. In this chapter we will build that picture step by step, treat it honestly as a *model* — a useful simplified story — and see how it explains why your iron tawa can stick to a fridge magnet while your aluminium bowl cannot.",{"id":1599,"type":1600,"tone":1601,"items":1602},"spec-18","spec","blue",[1603,1606,1609,1612],{"label":1604,"value":1605},"Typical domain size","about 0.001 mm to 0.1 mm across — smaller than a grain of sand, larger than a living cell",{"label":1607,"value":1608},"Atoms per domain","roughly 10 billion to 1 trillion atoms, each with electrons spinning like tiny current loops",{"label":1610,"value":1611},"Domains in a nail","billions of domains packed together, each with its own north-south direction",{"label":1613,"value":1614},"What we actually see","nothing; domains are inferred from experiments and patterns, not photographed directly",{"id":1616,"type":1617,"title":1618,"items":1619},"steps-19","steps","How domains create 'no magnetism' in ordinary iron",[1620,1623,1626,1629,1632],{"title":1621,"text":1622},"Start with atomic magnets","Inside iron, every atom has electrons spinning. Each spinning electron acts like a tiny magnet. This is quantum behaviour, but we can picture it as a tiny arrow.",{"title":1624,"text":1625},"Form domains","Neighbouring atoms team up into domains, where all their tiny arrows point the same direction. A domain behaves like one small bar magnet.",{"title":1627,"text":1628},"Random directions","In unmagnetised iron, each domain points a different way. One domain points left, another up, another down-right, and so on.",{"title":1630,"text":1631},"Cancellation","Where two domains meet, a north pole faces a south pole. Their magnetic fields leak out, curve around, and cancel each other nearby.",{"title":1633,"text":1634},"Net effect","With no preferred direction, the billions of tiny fields add up to zero. The iron nail does not attract iron filings.",{"id":1636,"type":1503,"variant":1637,"title":1638,"markdown":1639},"callout-20","model_limit","Domains are a model, not a photograph","No one has ever looked inside an iron nail and seen little football teams wearing 'North' and 'South' jerseys. Domains are a **model**: a deliberately simplified picture that helps us predict what will happen. Scientists actually use quantum mechanics and complex mathematics to describe why iron is magnetic. The domain story is like describing a cricket match by saying 'the team decided to bat aggressively' — useful, easy to follow, but missing thousands of individual details. When we say 'domains line up,' we mean the real atomic magnets behave *as if* they formed such teams.",{"id":1641,"type":1472,"markdown":1642},"prose-21","Now imagine stroking that same nail with a strong bar magnet, north pole to tip, again and again. Something changes. The domains that happened to point near the stroking direction grow larger. Domains pointing other directions shrink, split, or rotate. After enough strokes, most domains point the same way. The nail now has a net north pole at one end and a south pole at the other. It picks up paper clips. The invisible teams have been given a common captain.",{"id":1644,"type":1512,"title":1645,"problem":1646,"steps":1647},"worked-example-22","Calculating how domain alignment changes the field","An iron nail is placed near a strong magnet. Before stroking, it has 1000 domains pointing randomly in all directions, giving zero net field. After stroking, 800 domains point roughly north and 200 still point randomly. If each aligned domain contributes a tiny field of 2 microtesla and each random domain averages to zero, what is the approximate net field of the nail?",[1648,1649,1650,1651,1652],"First, identify which domains matter. The 200 random domains cancel each other out and contribute approximately zero to the net field.","Calculate the contribution from aligned domains: 800 domains × 2 microtesla each = 1600 microtesla total if they all acted alone.","However, domains do not simply add like numbers. In reality the material's shape and内部 structure mean only a fraction appears outside. For this model, we treat the aligned contribution as the dominant term and the random term as negligible.","Net field ≈ 1600 microtesla = 1.6 millitesla. For comparison, Earth's magnetic field is about 25–65 microtesla. The nail's surface field is therefore roughly 25–60 times stronger than Earth's field, enough to move a compass needle or lift a small paper clip.","This worked example uses the domain model to connect invisible atomic behaviour to a measurable number, showing why the model is useful even though it simplifies quantum reality.",{"id":1654,"type":1485,"prompt":1655,"options":1656,"explanation":1663},"prediction-23","You have two identical iron rods. Rod A is heated red-hot and then cooled in Earth's magnetic field, pointing north-south. Rod B is heated red-hot and cooled lying east-west. Both are then tested with iron filings. What do you predict?",[1657,1659,1661],{"id":1560,"label":1658},"Both rods attract filings equally strongly.",{"id":1563,"label":1660},"Rod A attracts filings weakly; Rod B shows almost no attraction.",{"id":1566,"label":1662},"Both rods lose all magnetism permanently from heating.","The correct answer is that Rod A (b) may show weak magnetisation and Rod B almost none. When iron cools through its Curie temperature, its domains can form in alignment with any external field present. Earth's field is weak but present. Rod A, pointing north-south during cooling, can pick up some weak domain alignment along that axis. Rod B, perpendicular to Earth's field, has no preferred direction for domains to lock into. However, this effect is subtle and requires careful isolation from other fields. Many textbooks simplify this; in practice both rods might show very weak effects unless the experiment is carefully controlled. This illustrates both the power and the limits of the domain model.",{"id":1665,"type":1553,"itemId":1666,"prompt":1667,"check":1668,"hints":1677,"feedback":1681},"practice-24","magnets.p002","A student claims: 'If I cut a magnetised iron nail in half, I get one piece with only north pole and one piece with only south pole.' Use the domain model to explain what actually happens, then choose the correct description.",{"kind":1557,"options":1669,"correct":1676},[1670,1672,1674],{"id":1560,"label":1671},"Each half has a north pole at one end and a south pole at the other, but weaker.",{"id":1563,"label":1673},"One half becomes pure north; the other becomes pure south.",{"id":1566,"label":1675},"Both pieces lose all magnetism instantly.",[1560],[1678,1679,1680],"Think about what domains look like inside each half after cutting.","Remember that domains themselves do not change when you cut; you just expose new surfaces.","Does cutting change the direction domains point inside each piece?",{"correct":1682,"incorrect":1683},"Exactly. Cutting exposes new end surfaces, but the domains inside each half still point the same way they did before. Each half becomes a smaller magnet with its own north and south poles. You cannot isolate a single pole this way — this is why magnetic monopoles remain hypothetical in classical magnetism.","Review the domain model. Cutting does not rotate domains or remove poles. Each half retains aligned domains, so each half must have both a north end and a south end. The magnetism is weaker simply because there is less aligned material, not because poles separate.",{"id":1685,"type":1476,"title":1686,"eyebrow":1687,"navLabel":1688},"chapter-25","Alignment Makes the Pull: How Magnetism Appears","Chapter 04","Alignment creates pull",{"id":1690,"type":1472,"markdown":1691},"prose-26","Picture a classroom full of students asked to face the blackboard. If they sit randomly—some facing the door, some the windows, some the board—the room looks chaotic and nothing much gets done. But when the teacher calls, \"All eyes on the board,\" suddenly every student turns the same way. The room has a clear direction.\n\nInside every piece of unmagnetised iron, billions of tiny magnetic teams called domains are just like those students before the teacher speaks. Each domain has its own tiny north and south pole, but they point in every possible direction. One domain's north pole points left, another's points up, another's points right. Because they are jumbled, their tiny magnetic fields cancel each other out, like equal teams pulling in opposite directions. The iron shows no overall magnetism; it will not attract a pin at a distance.\n\nMagnetism appears when something forces most of these domains to rotate and point the same way. This chapter explains how that alignment happens, why it makes a pull we can feel, and why some materials hold their new formation while others slip back into chaos the moment the external force disappears.\n\nWe will use a labelled model of domains. A model is a simplified story we tell to explain what we observe; we cannot photograph a domain with an ordinary camera, but the model correctly predicts what happens when we stroke iron with a magnet or heat it and drop it.",{"id":1693,"type":1503,"variant":1694,"title":1695,"markdown":1696},"callout-27","definition","Domain alignment","**Domain alignment** means the condition in which most magnetic domains inside a material are rotated so that their north poles point in roughly the same direction. When domains align, their individual magnetic fields add together instead of cancelling, producing a net magnetic field with clear north and south poles.",{"id":1698,"type":1617,"title":1699,"items":1700},"steps-28","How stroking magnetises a piece of iron",[1701,1705,1709,1713,1717],{"title":1702,"tag":1703,"text":1704},"Start with jumbled domains","Before","The iron nail contains domains pointing randomly. No net north or south pole exists. The nail does not attract iron filings at a distance.",{"title":1706,"tag":1707,"text":1708},"Apply a strong external field","During","Stroke one end of the nail with the same pole of a strong bar magnet, always moving in the same direction. Each stroke applies a magnetic force to the domains.",{"title":1710,"tag":1711,"text":1712},"Domains rotate","Change","Domains closest to the magnet's pole feel the strongest pull. They swivel so their internal north poles point away from the magnet's north pole (and toward its south pole).",{"title":1714,"tag":1715,"text":1716},"Alignment spreads","Spread","With repeated strokes in the same direction, more and more domains lock into parallel orientation. Their tiny fields begin to reinforce rather than cancel.",{"title":1718,"tag":1719,"text":1720},"Net pole appears","After","The nail now has a recognisable north pole at one end and a south pole at the other. It lifts iron filings and sticks to the refrigerator door.",{"id":1722,"type":1512,"title":1723,"problem":1724,"steps":1725},"worked-example-29","From zero pull to lifting five pins","An iron nail does not attract pins. After 20 single-direction strokes with a strong bar magnet, it lifts five pins. After heating the nail in a candle flame and cooling it, it lifts none. Explain what changed inside the nail at each stage.",[1726,1727,1728],"Before stroking: The nail's domains are randomly oriented. For every domain with its north pole pointing toward the pin, another points away. The vector sum of all tiny fields is approximately zero. No net field reaches the pin.","After 20 strokes: Each stroke exerts a torque on domains near the surface. Repeated strokes in the same direction rotate domains so a majority point the same way—say, 70 percent aligned. Their fields add. The nail now has a net north pole at one tip and a south pole at the other. The field extends far enough to magnetise the steel pins temporarily, causing attraction. The nail lifts five pins.","After heating and cooling: Thermal energy makes atoms vibrate violently. This random motion jostles domains back into random directions. When the nail cools, the domains freeze in a new disordered arrangement. The fraction aligned drops back near 50\u002F50. B_net returns to nearly zero. The nail again lifts no pins.",{"id":1730,"type":1731,"caption":1732,"columns":1733,"rows":1737},"table-30","table","Soft iron versus steel after alignment",[1734,1735,1736],"Property","Soft iron","Steel",[1738,1742,1746,1750,1754,1758],[1739,1740,1741],"Ease of domain alignment","Very easy; domains swivel freely","Harder; domains resist rotation",[1743,1744,1745],"External field needed","Weak field sufficient","Stronger field needed",[1747,1748,1749],"Time to align","Few strokes","Many strokes",[1751,1752,1753],"Retention after field removed","Poor; domains jumble quickly","Good; domains stay locked",[1755,1756,1757],"Everyday use","Electromagnet cores (relay, bell)","Permanent magnets, compass needles",[1759,1760,1761],"Model reason","Low 'friction' between domains","High 'friction' or crystal pinning",{"id":1763,"type":1485,"prompt":1764,"options":1765,"explanation":1778},"prediction-31","You stroke two identical-looking nails 20 times each with the same bar magnet. Nail A is soft iron. Nail B is steel. You then try to lift iron filings from a tray. What do you predict?",[1766,1769,1772,1775],{"id":1767,"label":1768},"same","Both nails lift exactly the same amount.",{"id":1770,"label":1771},"soft-more","Nail A lifts more immediately after stroking, but loses its pull within an hour.",{"id":1773,"label":1774},"steel-more","Nail B lifts more immediately after stroking and stays strong for days.",{"id":1776,"label":1777},"neither","Neither nail lifts anything because stroking cannot create magnetism.","The correct choice is 'soft-more.' Soft iron domains align very easily during stroking, so Nail A shows strong magnetism immediately. However, because those domains are also free to jumble, Nail A loses most of its magnetism within minutes to hours. Steel domains resist alignment initially, so Nail B may lift slightly less right after stroking, but it retains magnetism far longer. 'Nail B lifts more immediately' is the common mix-up; students confuse 'harder to align' with 'weaker when aligned.'",{"id":1780,"type":1553,"itemId":1781,"prompt":1782,"check":1783,"hints":1794,"feedback":1798},"practice-32","magnets.p003","A blacksmith heats a steel chisel until it glows red, then hammers it on an anvil while it cools. Why might the chisel become *less* magnetic than before, even though steel normally keeps its domains aligned?",{"kind":1557,"options":1784,"correct":1793},[1785,1787,1789,1791],{"id":1560,"label":1786},"Hammering always creates magnetism, so the chisel should become more magnetic.",{"id":1563,"label":1788},"Heat and mechanical vibration randomise domains, overwhelming steel's natural tendency to stay aligned.",{"id":1566,"label":1790},"Steel turns into copper when heated, and copper has no domains.",{"id":1569,"label":1792},"The chisel's mass decreases, so it has fewer domains total.",[1563],[1795,1796,1797],"Think about what happens to domains during both heating and hammering.","Consider whether steel's 'good retention' can be overcome by strong disorder.","Remember: the question asks why the chisel becomes *less* magnetic, not more.",{"correct":1799,"incorrect":1800},"Correct. Heat gives atoms enough kinetic energy to jostle domains out of alignment. Hammering adds mechanical vibration that also randomises domain directions. Together, these effects can overcome steel's tendency to retain alignment, leaving the chisel with weaker net magnetism than before.","Think again. Hammering does not create magnetism—it shakes domains. Heat adds energy that randomises direction. Steel resists disorder, but strong heating and vibration together can overwhelm that resistance.",{"id":1802,"type":1472,"markdown":1803},"prose-33","The key insight of this chapter is that magnetism is not created from nothing when you stroke iron. The domains were already there, magnetic all along, merely hiding in plain sight because they pointed every which way. Alignment reveals what was always present. Disorder conceals it again.\n\nThis is why a magnetised steel needle stays magnetic for years while a soft iron nail forgets its magnetism before the end of a school period. The same domains exist in both. The difference is how stubbornly they hold their formation. We will use this idea in later chapters when we ask why electromagnets use soft iron cores, why compasses need steel needles, and why dropping a magnet on a hard floor can slowly ruin it—not by breaking domains, but by jarring them out of step.",{"id":1805,"type":1476,"title":1806,"eyebrow":1807,"navLabel":1808},"chapter-34","Why Copper and Aluminium Refuse to Stick","Chapter 05","Why others refuse",{"id":1810,"type":1472,"markdown":1811},"prose-35","You already know that an iron nail leaps toward a magnet while a wooden pencil stays still. But what about metals that look shiny and solid yet refuse to stick? Hold a neodymium magnet near an aluminium window frame or a copper water pipe. Nothing happens. No tug, no click, no slow creep across the gap. Aluminium and copper are metals. They carry electric current. They even feel warm in summer. So why does the magnet act as if they are invisible?\n\nThe answer lies inside the atoms, but it is not enough to say \"copper has atoms.\" Every solid has atoms. The real question is what those atoms *do* when a magnet comes close. In iron, tiny groups of atoms called **domains** can swing together like rows of tiny compass needles, all pointing the same way, and that organised team creates the pull you feel. In copper and aluminium, such teams either never form or fall apart faster than you can blink. To understand why, we must look at how electrons behave inside each kind of metal.",{"id":1813,"type":1503,"variant":1694,"title":1814,"markdown":1815},"callout-36","Paramagnetic and diamagnetic","**Paramagnetic** materials have atoms whose electrons create tiny magnetic fields, but these fields point randomly and cancel out. A strong external magnet can nudge them slightly, but they snap back when the magnet is removed. **Diamagnetic** materials develop weak opposite fields when exposed to a magnet, actually pushing away very slightly. Most non-magnetic metals, including copper and aluminium, fall into one of these categories.",{"id":1817,"type":1472,"markdown":1818},"prose-37","In iron, each atom behaves like a tiny magnet because of how its electrons spin and orbit. Crucially, neighbouring iron atoms *talk* to each other. They encourage their neighbours to point the same way, and groups of millions or billions of atoms lock into stable **domains**. When you bring a magnet near, whole domains rotate together. That massive, organised response is what you feel as attraction.\n\nCopper and aluminium atoms also contain spinning electrons, but the arrangement of their electron shells is different. The outer electrons in copper areShared so freely between atoms that they form a **sea of electrons**, good for carrying current but poor at locking neighbouring atoms into magnetic alignment. In aluminium, the electron configuration similarly prevents the strong neighbour-to-neighbour *exchange interaction* that builds stable domains. Without domains, there is no large team of atoms waiting to swing into line. Each atom responds alone, and its response is swamped by thermal jiggling at ordinary temperatures.",{"id":1820,"type":1512,"title":1821,"problem":1822,"steps":1823},"worked-example-38","The moving magnet over copper: a hidden effect","Take a strong neodymium magnet and drop it through a copper pipe or through a slit in a thick copper plate. The magnet falls very slowly, as if the copper is grabby. Yet holding the magnet still against the copper gives no pull at all. Why?",[1824,1825,1826,1827,1828],"With the magnet still, copper acts non-magnetic. No domains align, no force.","When the magnet moves, its changing magnetic field pushes on copper's free electrons (the electron sea).","The moving electrons form tiny electric currents, called eddy currents, which create their own magnetic field.","By Lenz's law, that new field opposes the change—pushing back on the falling magnet and slowing it down.","This is not the magnet attracting copper directly. It is the magnet inducing electricity, and that electricity pushing back. The effect shows copper *does* respond to magnetic fields, but through electrical induction, not domain alignment.",{"id":1830,"type":1503,"variant":1504,"title":1831,"markdown":1832},"callout-39","\"All metals are magnetic\"","A common mix-up, especially after seeing iron stick so well, is to assume every shiny metal behaves the same. Copper wires, aluminium foil, gold jewellery, and silver coins are all metals, yet none sticks to a magnet. Being a metal means good electrical conduction; being *magnetic* requires a specific arrangement of electrons that lets domains form and stay organised. Metals are a large club; magnetic metals are a small subgroup.",{"id":1834,"type":1553,"itemId":1835,"prompt":1836,"check":1837,"hints":1846,"feedback":1850},"practice-40","magnets.p004","Riya has five metal samples: iron nail, steel spoon, copper wire, aluminium foil, and brass key. Her magnet picks up only the iron nail and steel spoon. She concludes, \"Only iron and steel are real metals.\" What is wrong with her reasoning?",{"kind":1557,"options":1838,"correct":1845},[1839,1841,1843],{"id":1560,"label":1840},"Copper, aluminium and brass are not metals at all.",{"id":1563,"label":1842},"The magnet test checks magnetism, not whether something is a metal.",{"id":1566,"label":1844},"The magnet is too weak to test copper and aluminium.",[1563],[1847,1848,1849],"Think about what property the magnet actually reveals.","Consider whether aluminium foil conducts electricity.","Brass is an alloy of copper and zinc—both metals.",{"correct":1851,"incorrect":1852},"Exactly. The magnet test detects magnetic response (domain alignment), not metallic character. Copper, aluminium and brass are genuine metals; they simply lack stable magnetic domains. Riya confused one property for another.","Look again. The magnet test shows whether a material has domains that can align. Many metals do not, yet they are still metals. Conductivity, malleability and chemical behaviour confirm their metallic nature.",{"id":1854,"type":1581,"title":1855,"points":1856},"summary-41","What to remember",[1857,1858,1859,1860,1861],"All materials contain atoms with electrons, but only some can form stable magnetic domains.","Iron's strong exchange interaction lets neighbour atoms lock into aligned domains; copper and aluminium lack this.","Thermal motion at room temperature randomises any tiny alignment in copper and aluminium, so no net pull appears.","Copper and aluminium still respond to moving magnetic fields, but through electrical induction (eddy currents), not domain alignment.","The magnet test tests magnetism, not whether something is a metal. Many non-magnetic metals exist.",{"id":1863,"type":1476,"title":1864,"eyebrow":1865,"navLabel":1866},"chapter-42","Permanent Versus Temporary: Steel Spoon Versus Iron Nail","Chapter 06","Permanent vs temporary",{"id":1868,"type":1472,"markdown":1869},"prose-43","Take a steel spoon from your kitchen and an iron nail from a toolbox. Both contain iron atoms, both look metallic, and both will cling to a strong magnet. Yet if you try to turn each one into a magnet by stroking it with a bar magnet, they behave very differently afterwards. The steel spoon will pick up smaller spoons for months. The iron nail will lift pins with excitement for an hour or two, then suddenly give up and drop everything. Why does one stay magnetic while the other forgets?\n\nThe answer lies not in what the two objects are made of, but in how their internal structure holds onto the invisible alignment we call magnetism. In this chapter we explore the difference between **permanent magnets** and **temporary magnets** through the language of domains—the tiny teams of aligned atoms you met in Chapter 3. We will see why steel locks its domains in place, why iron lets them slip away, and how heat, dropping, or hammering can destroy either kind of magnet.",{"id":1871,"type":1600,"tone":1872,"items":1873},"spec-44","copper",[1874,1878,1882,1886],{"label":1875,"big":1876,"value":1877},"Steel spoon after stroking","weeks to years","Retains strong magnetism; domains stay locked by rigid crystal structure.",{"label":1879,"big":1880,"value":1881},"Iron nail after stroking","minutes to hours","Acts magnetic briefly; domains randomise again due to softer crystal structure.",{"label":1883,"big":1884,"value":1885},"Curie temperature (iron)","770 °C","Above this, thermal motion destroys all domain alignment permanently.",{"label":1887,"big":1888,"value":1889},"Curie temperature (nickel)","1128 °C","Same effect; different element, different threshold.",{"id":1891,"type":1503,"variant":1694,"title":1892,"markdown":1893},"callout-45","Permanent magnet vs temporary magnet","A **permanent magnet** is a material that keeps its magnetic properties for a long time after the magnetising force is removed; its domains remain aligned because the crystal structure makes it hard for them to rotate back.\n\nA **temporary magnet** becomes magnetic only while near another magnet or current, or for a short time after being stroked; its domains align easily under influence but also slip back to random orientations easily. Soft iron is the classic temporary magnet. Steel, once magnetised, is the everyday permanent magnet you find on refrigerator doors and in speakers.",{"id":1895,"type":1472,"markdown":1896},"prose-46","To understand why steel and iron differ, picture the inside of each metal as a city full of tiny compass needles—our domain groups from earlier chapters. In **soft iron**, the streets are wide and the needles sit on loose pivots. When a bar magnet strokes past, every needle spins to face the same direction instantly. But the moment the bar magnet walks away, wind and traffic jostle the needles. Within hours they point every which way again, and the city's organised field collapses into chaos.\n\nIn **steel**, the streets are narrow and the needles are jammed into tight sockets. The act of stroking still forces them to align, but once the bar magnet is gone, each needle is physically locked where it stands. Thermal vibrations still nudge them, yet the crystal lattice is too rigid to let them rotate freely. Months pass before enough needles drift out of place to matter. This is why your stainless steel tools and alnico speaker magnets stay magnetic across monsoons and summers.",{"id":1898,"type":1512,"title":1899,"problem":1900,"steps":1901},"worked-example-47","Stroking a steel spoon and an iron nail: what happens?","You have a bar magnet, a steel spoon, and an iron nail. You stroke each one fifty times in the same direction with the same pole of the bar magnet. Two hours later, you test which object can lift a paper clip. One week later, you test again. Predict and explain the results at each stage.\n\nAssume room temperature (~30 °C) and no dropping or heating.",[1902,1903,1904,1905,1906],"Stroke both objects fifty times from handle to tip, always with the north pole of the bar magnet leading the motion. This forces domains in each object to align along the stroke direction.","Immediately after stroking, both the spoon and the nail lift the paper clip. Domains in each are freshly aligned; each object now has a north and south pole.","Test again at two hours. The steel spoon still lifts the clip. The iron nail may already fail or lift weakly. Atomic vibrations in iron's softer lattice have allowed domains to begin rotating back to random orientations.","Test again at one week. The steel spoon lifts the clip confidently. The iron nail behaves like ordinary unmagnetised iron; its domains have fully randomised. The steel's rigid crystal structure preserves most of the original alignment.","If either object were heated above its Curie temperature after stroking, both would lose magnetism completely. Thermal energy would overcome even steel's locking effect and randomise domains instantly.",{"id":1908,"type":1503,"variant":1504,"title":1909,"markdown":1910},"callout-48","\"Harder to magnetise means weaker magnet\"","Many students think steel must make a poor magnet because it is harder to magnetise than iron. The opposite is true. Steel resists both magnetisation and demagnetisation. You must stroke it longer or use a stronger field to align its locked domains in the first place, but once aligned, they stay aligned. This trade-off—*harder to create, harder to destroy*—makes steel ideal for permanent magnets. Iron's easy-come-easy-go nature suits it for transformer cores and relay switches, where magnetism must flip on and off instantly.",{"id":1912,"type":1913,"title":1914,"scale":1915,"rungs":1916},"ladder-49","ladder","How long magnetism lasts in everyday materials after stroking","linear",[1917,1921,1925,1929,1932,1935],{"label":1918,"value":1919,"display":1920},"Soft iron nail (untreated)",0.002,"~1 hour",{"label":1922,"value":1923,"display":1924},"Transformer iron silicon steel",0.02,"~1 day",{"label":1926,"value":1927,"display":1928},"Pure nickel (soft)",0.1,"~1 week",{"label":1930,"value":44,"display":1931},"Carbon steel (knife)","~1 month",{"label":1933,"value":787,"display":1934},"Alnico alloy (loudspeaker)","~1 year",{"label":1936,"value":1937,"display":1938},"Neodymium (hard drives, earbuds)",120,"~10 years",{"id":1940,"type":1485,"prompt":1941,"options":1942,"explanation":1951},"prediction-50","You find two identical-looking metal rods in a school lab. Rod A becomes strongly magnetic after ten strokes and stays magnetic for a month. Rod B becomes strongly magnetic after five strokes but loses nearly all magnetism overnight. Which statement is most likely true?",[1943,1945,1947,1949],{"id":1560,"label":1944},"Rod A is iron; Rod B is steel.",{"id":1563,"label":1946},"Rod A is steel; Rod B is iron.",{"id":1566,"label":1948},"Rod A was heated before testing.",{"id":1569,"label":1950},"Rod B contains no iron at all.","The correct answer is **b**. Steel requires more effort to magnetise (ten strokes versus five) because its rigid crystal structure resists domain alignment, but it retains that alignment for a long time. Iron magnetises easily with few strokes but loses alignment quickly as domains randomise. Heating would demagnetise both, not explain a difference in how they respond to stroking. A non-iron rod would not become magnetic in the first place.",{"id":1953,"type":1503,"variant":1637,"title":1954,"markdown":1955},"callout-51","The 'locked needle' picture is a simplification","We describe steel domains as 'locked in place' and iron domains as 'free to rotate.' Real crystals contain defects, grain boundaries, and impurities that pin domains more subtly. Some specially treated irons can act semi-permanent, and some cheap steels demagnetise faster than expected. Our locked-versus-loose model captures the main classroom distinction, but materials engineers use hysteresis curves and coercivity numbers to make precise predictions. Treat our picture as a useful first map, not a perfect replica of atomic reality.",{"id":1957,"type":1476,"title":1958,"eyebrow":1959,"navLabel":1960},"chapter-52","The Earth Magnet and How Compasses Obey Domains","Chapter 07","Earth's domain lesson",{"id":1962,"type":1472,"markdown":1963},"prose-53","Imagine you are standing on a quiet beach in Gujarat, holding a small compass. The needle swings for a moment, then settles — one end pointing steadily toward the north, the other toward the south. But the compass needle is not searching for the North Star. It is doing something much stranger: it is lining up with an invisible force that wraps around our entire planet. That force is Earth's magnetic field, and the compass obeys it for the same reason a paperclip leaps toward a bar magnet. Inside the compass needle, tiny magnetic domains are rotating to align with an external field. Only this time, the external field belongs to Earth itself — a magnet so large that you can stand inside it without ever noticing. In this chapter, we will see how the domain idea from the last chapter explains the compass, why sailors once carried lodestone, and why the compass's \"north pole\" actually points toward Earth's magnetic south pole. The story begins with a rock that ancient sailors already knew was special.",{"id":1965,"type":1966,"title":1967,"items":1968},"timeline-54","timeline","From Lodestone to Gilbert's Earth Magnet",[1969,1973,1977,1981],{"time":1970,"title":1971,"text":1972},"~600 BCE","Greeks find lodestone","Sailors near Magnesia discover a rock that attracts iron. They call it 'lodestone' (leading stone). Its domains were aligned by cooling slowly in Earth's field over millions of years.",{"time":1974,"title":1975,"text":1976},"~100 CE","Chinese compass needles","Craftsmen shape lodestone into spoons and needles that always point north-south when freely suspended. Domain alignment with Earth's field becomes a navigation tool.",{"time":1978,"title":1979,"text":1980},"1180s","Compass reaches Europe","Sailors cross the Mediterranean with magnetised needles on floating straw or pivoted stands. Voyages become safer because the needle does not need stars or landmarks.",{"time":1982,"title":1983,"text":1984},"1600","Gilbert publishes De Magnete","William Gilbert shows Earth itself is a magnet. He maps how compass needles tilt downward at different latitudes — proof the field is global, not just local attraction.",{"id":1986,"type":1472,"markdown":1987},"prose-55","How does the compass needle know which way to point? Recall that a magnetic domain is a tiny region inside iron where billions of atomic magnets point the same way. In an unmagnetised iron bar, these domains face random directions, so their fields cancel out. In a compass needle — made of magnetised steel — the domains are already mostly aligned. But the needle is small and light, mounted on a nearly frictionless pivot. When you place it in Earth's magnetic field, the field exerts twisting forces on every domain. Even though Earth's field is feeble compared to a bar magnet's field near its pole, it is enough to turn the whole needle until the domains point along the field lines. The needle's north-seeking end points north because opposite poles attract: the needle's north pole is pulled toward Earth's magnetic south pole. This is a subtle but crucial point, and it causes more confusion in classrooms than almost any other idea in magnetism.",{"id":1989,"type":1503,"variant":1504,"title":1990,"markdown":1991},"callout-56","\"North attracts north\" — why this feels true but is not","Many students say the compass's north pole points north because Earth's north pole attracts it. Actually, opposite poles attract and like poles repel. Earth's magnetic south pole sits near geographic north. So the compass north pole is attracted to Earth's magnetic south pole.\\n\\nWhy the confusion? Geographers named the geographic poles long before anyone understood magnetism. The place we call 'North' happens to be where Earth's magnetic field lines enter the ground — behaviour associated with a south magnetic pole. Think of it this way: the compass is honest about poles, but human map-makers named the continents first.",{"id":1993,"type":1512,"title":1994,"problem":1995,"steps":1996},"worked-example-57","Why does a compass needle dip in Norway but lie flat in Kerala?","William Gilbert noticed that near London, a freely suspended compass needle did not just point north-south; it also tilted downward, nose-first into the ground. Near the equator, the same needle stayed nearly horizontal. Explain this using the domain alignment model and Earth's shape.",[1997,1998,1999,2000],"Picture Earth's field as if a giant bar magnet sat inside the planet, tilted about 11° from the rotation axis. Field lines emerge near Antarctica and re-enter near the Arctic.","At the magnetic equator — roughly parallels of latitude like Kerala's — field lines run parallel to the ground. A compass needle's domains align horizontally because the field itself is horizontal there.","At high latitudes like Norway or Canada, field lines plunge steeply into the ground as they approach the magnetic pole. The needle's domains try to align with these diving lines, so the north-seeking end tilts downward.","Gilbert called this tilt the 'magnetic dip.' He measured it with a needle on a horizontal axle. Different dip angles at different latitudes proved the field is global and centred inside Earth, not just a local trick of surface rocks.",{"id":2002,"type":1600,"tone":1601,"items":2003},"spec-58",[2004,2008,2012],{"label":2005,"big":2006,"value":2007},"Field strength at surface","25–65 µT","Earth's magnetic field is 100–1000 times weaker than a refrigerator magnet's surface field, yet enough to align compass domains.",{"label":2009,"big":2010,"value":2011},"Pole drift speed","~40 km\u002Fy","Earth's magnetic north pole wandles; compasses need periodic map updates. In 2019, navigators revised the World Magnetic Model early.",{"label":2013,"big":2014,"value":2015},"Reversal timescale","~200 k–300 ky","The poles flip unpredictably. The last reversal was 780,000 years ago. Rocks record past flips through frozen domain orientations.",{"id":2017,"type":2018,"title":2019,"questions":2020},"quiz-59","quiz","Quick check: Earth, domains and compasses",[2021,2032,2043],{"itemId":2022,"prompt":2023,"options":2024,"correct":1563,"why":2031},"magnets.q005","Why does a compass needle align with Earth's field even though that field is very weak?",[2025,2027,2029],{"id":1560,"label":2026},"The needle is made of heavy iron that drags toward Earth's centre",{"id":1563,"label":2028},"The needle rests on a frictionless pivot, so even weak torque rotates it",{"id":1566,"label":2030},"Earth's field is actually stronger than a bar magnet's field at all points","A compass needle is tiny and nearly free to turn. Weak torque from Earth's field, applied over many seconds, is enough to swing domains into alignment. The needle's low mass and low friction matter as much as the field itself.",{"itemId":2033,"prompt":2034,"options":2035,"correct":1563,"why":2042},"magnets.q006","The compass needle's north pole points toward geographic north. What magnetic pole of Earth is located there?",[2036,2038,2040],{"id":1560,"label":2037},"Earth's magnetic north pole",{"id":1563,"label":2039},"Earth's magnetic south pole",{"id":1566,"label":2041},"Earth has no magnetic poles, only electric ones","Opposite poles attract. The needle's north pole is pulled toward Earth's magnetic south pole, which happens to sit near geographic north. Geographers named the top of the map before physicists named magnetic poles.",{"itemId":2044,"prompt":2045,"options":2046,"correct":1563,"why":2053},"magnets.q007","Lodestone is naturally magnetic iron oxide. What aligned its domains long ago?",[2047,2049,2051],{"id":1560,"label":2048},"Lightning strikes only",{"id":1563,"label":2050},"Slow cooling in Earth's magnetic field over millions of years",{"id":1566,"label":2052},"Ancient blacksmiths hammered it in one direction","As molten iron oxide cooled below its Curie temperature, domains could form and freeze into alignment with Earth's field. Lightning can magnetise rocks, but lodestone's widespread, uniform alignment points to Earth's persistent field.",{"id":2055,"type":697,"prompt":2056},"reflection-60","Look at a map of India. If you carried a compass from Kanyakumari to Srinagar, the needle would gradually tilt more steeply downward as you travelled north. Sketch what you think the field lines look like entering the ground near the magnetic pole, and write one sentence about why this dip convinced Gilbert that Earth itself is the magnet.",{"id":2058,"type":1476,"title":2059,"eyebrow":2060,"navLabel":2061},"chapter-61","Mix-Up Alley: Metals, Distance and Shielding","Chapter 08","Common mix-ups",{"id":2063,"type":1472,"markdown":2064},"prose-62","Walk into any school staff room and you will hear the same bets: \"A one-rupee coin must stick because it is metal.\" \"Wrap the magnet in a hanky and it will pull just as hard.\" \"My big fridge magnet can lift more than your tiny one.\" These guesses feel sensible, but two out of three are usually wrong. This chapter is a walk down Mix-Up Alley — three common traps that even adults fall into — and a chance to build your own lie-detector for magnet claims. The tool you will practise is the fair test: change only one thing, keep everything else the same, and let the magnet speak for itself.",{"id":2066,"type":1503,"variant":1504,"title":2067,"markdown":2068},"callout-63","Mix-Up 1: \"Every metal is magnetic\"","**Why it feels right:** Most strong magnets in Indian homes are black, heavy and metallic-looking, so our brains quietly file \"metal = magnetic.\" \n\n**Why it is wrong:** Only iron, nickel, cobalt and a few special alloys (like alnico or some stainless steels) have atoms that can form magnetic domains. Copper, aluminium, brass, gold and silver have electrons arranged differently; their domains either do not form or cancel out completely. A post-2004 Indian one-rupee coin is mostly stainless steel with some nickel and therefore may show a faint tug, but a pure copper wire or a brass door handle will not stick at all. The rule is: *metal does not mean magnetic*.",{"id":2070,"type":1485,"prompt":2071,"options":2072,"explanation":2084},"prediction-64","You have three objects on your desk: a steel staple, a copper wire from an old charger, and an aluminium foil ball. You bring a bar magnet slowly toward each. What happens?",[2073,2075,2078,2081],{"id":1489,"label":2074},"All three objects will jump to the magnet",{"id":2076,"label":2077},"steel","Only the steel staple will stick",{"id":2079,"label":2080},"steel-copper","The steel staple and the copper wire will stick",{"id":2082,"label":2083},"aluminium","Only the aluminium foil will stick, because it is shiny like metal","Only the steel staple will stick. Steel is mostly iron, so it has magnetic domains that can align with the magnet's field. Copper and aluminium are metals, but their internal electron arrangement does not allow strong domain alignment. The aluminium foil may feel a tiny, almost invisible push or pull if the magnet moves very fast — a different effect called electromagnetic induction, not ordinary magnetism — but it will not stick. Many people pick \"all three\" or \"steel and copper\" because the word \"metal\" tricks us into grouping them together.",{"id":2086,"type":1503,"variant":1637,"title":2087,"markdown":2088},"callout-65","Mix-Up 2: \"Magnetism passes through anything\"","**The everyday model:** We imagine the magnetic field as an invisible arm that reaches through cloth, wood, plastic or air without getting tired.\n\n**The reality:** The field does pass through non-magnetic materials, but it gets *weaker* with distance. Every millimetre of wood, plastic or paper between magnet and object weakens the pull. More importantly, iron and some steels *absorb* and redirect field lines; they act like a shield. Sandwich a steel nail between the magnet and a steel paper clip and the clip may no longer feel enough force to lift. The field lines prefer the easy path through iron rather than jumping across air to the clip. So magnetism does not pass through *everything equally* — distance matters, and iron can block it.",{"id":2090,"type":1512,"title":2091,"problem":2092,"steps":2093},"worked-example-66","Does a hanky stop a magnet?","A child claims: \"If I wrap my magnet in a cotton handkerchief, it will still lift the same number of paper clips because the field goes through cloth.\" Design a fair test and predict the result.",[2094,2095,2096,2097,2098,2099],"Keep the same magnet and the same paper clips. Do not change magnet size, clip size or room temperature.","First, lift clips with the bare magnet touching the first clip. Count how many hang in a chain. Record this number.","Next, wrap the magnet in one layer of cotton hanky. Lift clips again. Count.","Add a second layer, then a third, repeating the test each time.","Compare the counts. You will find fewer clips hang as layers increase. The field weakens with distance, even through cloth.","Now swap the hanky for a thin iron washer placed between magnet and clip. Even one washer drops the count sharply, because iron provides an easier path for field lines than air does.",{"id":2101,"type":1553,"itemId":2102,"prompt":2103,"check":2104,"hints":2115,"feedback":2119},"practice-67","magnets.p008","A shopkeeper says her large, flat ceramic fridge magnet (8 cm wide) is \"obviously stronger\" than a tiny neodymium button magnet (1 cm wide) because \"bigger is stronger.\" You have both magnets, a pile of identical steel washers, a ruler and a stopwatch. Design one fair test to check who is right.",{"kind":1557,"options":2105,"correct":2114},[2106,2108,2110,2112],{"id":1560,"label":2107},"Count how many washers each magnet lifts when touching them directly",{"id":1563,"label":2109},"Time how long each magnet stays stuck to the fridge before falling off naturally",{"id":1566,"label":2111},"Measure how far from a washer each magnet can be before the washer jumps to it",{"id":1569,"label":2113},"Weigh both magnets on a kitchen scale and compare grams",[1560,1566],[2116,2117,2118],"Think: what does \"stronger\" mean for a magnet? Its ability to pull things, not its weight or clock time.","A fair test must use the same object being pulled (same washers) and the same conditions for both magnets.","Distance matters. A strong magnet can pull from farther away.",{"correct":2120,"incorrect":2121},"Both A and C work. Counting washers tests direct pulling power. Measuring jump distance tests how far the field reaches — a sign of true strength. Neodymium wins even though it is tiny, because material matters more than size.","B measures glue or friction on the fridge, not magnetic strength. D confuses mass with magnetism. Try again: what test uses the magnet's pull on the same steel object?",{"id":2123,"type":1472,"markdown":2124},"prose-68","Here is where the three mix-ups tangle together in real life. Suppose you are helping sort scrap metal for a kabadi wallah. A heap looks like \"all metal,\" but the aluminium frames and copper wires will not cling to your magnet. If you try to pull a steel rod from under a thick wooden plank, the magnet may fail not because the rod is non-magnetic, but because the gap is too large. And if you bring a huge but weak decorative magnet, it may lose to a tiny neodymium disc from an old earphone. In each case, the mistake is the same: assuming one obvious fact (metal, thickness, size) tells the whole story, instead of running the object past the magnet itself.",{"id":2126,"type":697,"prompt":2127},"reflection-69","Look around the room you are in right now. Pick one object you think might be magnetic and one you are sure is not. What is your real reason — the material you guess inside, the colour, the weight, or something you have actually tested? How would you check without guessing?",{"id":2129,"type":1476,"title":2130,"eyebrow":2131,"navLabel":2132},"chapter-70","Electromagnets: When Electricity Organises Domains","Chapter 09","Electric organisers",{"id":2134,"type":1472,"markdown":2135},"prose-71","Walk past a scrapyard in any Indian city and you may see something surprising: a giant crane lifting a car body into the air with nothing but a flat metal disc. No hooks, no chains, no one tying ropes. The disc touches the car roof, the car rises, moves over a truck, and then — just drops. The secret is not a permanent magnet hidden inside that disc. It is an **electromagnet**: a magnet that switches on only when electricity runs through it, then switches off the moment the current stops. In this chapter we will see how electric current organises the same magnetic domains you already know, why this temporary power is useful, and where electromagnets appear from your mobile phone speaker to ISRO satellites.",{"id":2137,"type":1503,"variant":1694,"title":2138,"markdown":2139},"callout-72","Electromagnet","An **electromagnet** is a temporary magnet created by passing **electric current** through a coil of wire, usually with an **iron core** inside. The current forces the iron's magnetic domains to align. When the current stops, the domains randomise and the magnetism disappears.",{"id":2141,"type":1617,"title":2142,"items":2143},"steps-73","How current builds an electromagnet",[2144,2147,2150,2153,2156,2159],{"title":2145,"text":2146},"Wind the coil","Wrap insulated copper wire around an iron nail or bolt. The coil is called a **solenoid**. Insulation is essential so current flows around the iron, not straight across it.",{"title":2148,"text":2149},"Add the iron core","Place the iron nail inside the coil. The iron provides magnetic domains that can align. Without iron, the coil still makes a weak field; with iron, the field grows many times stronger.",{"title":2151,"text":2152},"Connect to a source","Join the coil ends to a battery or power supply. **Electric current** — a flow of electric charge — begins moving through the copper wire.",{"title":2154,"text":2155},"Domains align","The moving current creates a magnetic field around every loop of wire. Inside the iron, this field pushes neighbouring domains to point the same way, just like a permanent magnet.",{"title":2157,"text":2158},"Magnetism appears","The aligned domains add their fields together. The iron nail now attracts paper clips, iron filings, or any magnetic material nearby.",{"title":2160,"text":2161},"Switch off","Break the circuit. Current stops. Without the organising push, thermal motion randomises the domains. The nail drops the paper clips. Magnetism is gone.",{"id":2163,"type":1512,"title":2164,"problem":2165,"steps":2166},"worked-example-74","Crane scrapyard lift: how many cars can it hold?","A scrapyard electromagnet has a coil of 500 turns around a cylindrical iron core 30 cm across. When 10 amperes of current flow, it can lift 2,000 kg of scrap steel. A worker switches the current off by accident while the load is above a truck. What happens, and why is this safer with an electromagnet than with a permanent magnet?",[2167,2168,2169,2170,2171,2172],"When the switch opens, current drops to zero within milliseconds.","Without current, the magnetic field around the coil collapses.","The iron core's domains lose their organised alignment and return to random directions.","The magnetism disappears almost instantly. The 2,000 kg load falls straight into the truck — dangerous if a person is below, but exactly what the scrapyard wants for controlled dropping.","A permanent magnet of the same strength would keep holding the load even when the operator wanted release. Workers would need mechanical levers or heating to weaken it, wasting time and energy.","This on-off control is why scrapyards pay for electricity and complex wiring instead of using simple permanent magnets.",{"id":2174,"type":1503,"variant":1637,"title":2175,"markdown":2176},"callout-75","Our domain model oversimplifies copper","We have been treating copper and aluminium as \"non-magnetic\" because they do not stick to permanent magnets. Inside an electromagnet, copper is essential — but its role is to **carry current**, not to provide domains. A tiny, weak magnetic effect called **diamagnetism** actually exists in copper, but it opposes applied fields rather than strengthening them. In our domain model we ignore this because it does not change how electromagnets work in daily life. The model is labelled and stays useful, but it is not the full quantum-mechanical picture.",{"id":2178,"type":1472,"markdown":2179},"prose-76","Electromagnets do not live only in scrapyards. Inside your mobile phone, a tiny coil sits behind the speaker cone. When your music app sends changing electric currents, the coil becomes a magnet whose strength flickers thousands of times per second. This coil pushes and pulls against a nearby permanent magnet, vibrating the paper or plastic cone to create sound waves. No electromagnet, no phone calls, no短视频 audio. In hospitals, **MRI machines** use superconducting electromagnets — coils chilled to extremely low temperatures — to produce fields strong enough to align hydrogen atoms in your body. The signals from those atoms build detailed images of organs and tissues. Indian hospitals in cities like Chennai and Delhi operate dozens of MRI scanners that rely on this temporary, controllable magnetism. Research into **maglev trains**, which float above tracks to reduce friction, also depends on electromagnets that can be precisely switched and adjusted as the train moves. India has explored maglev corridors for high-speed routes, though none are in passenger service yet.",{"id":2181,"type":1503,"variant":2182,"title":2183,"markdown":2184},"callout-77","aha","ISRO's satellite trick","ISRO faces a problem in space: how do you hold two satellite parts together during launch, then release them cleanly in orbit? Springs alone might jam. Permanent magnets would stick forever. The answer is **electromagnetic separation systems**. A small electromagnet holds a latch firm while current flows. Once the satellite reaches the correct orbit, ground control sends a signal: current stops, domains randomise, the magnetic hold vanishes, and springs push the solar panel or instrument cover away. The on-off precision of domain alignment becomes a tool for space engineering. This is the same physics as the scrapyard crane, miniaturised and made failsafe.",{"id":2186,"type":1553,"itemId":2187,"prompt":2188,"check":2189,"hints":2200,"feedback":2204},"practice-78","magnets.p009","An ISRO engineer tests a small electromagnet for a satellite separation system. She wraps 100 turns of copper wire around a soft iron rod. With current on, the rod lifts 5 iron washers. She replaces the soft iron rod with an identical-sized wooden rod, keeps everything else the same, and switches on the same current. What happens to the number of washers lifted?",{"kind":1557,"options":2190,"correct":2199},[2191,2193,2195,2197],{"id":1560,"label":2192},"More washers, because wood is lighter",{"id":1563,"label":2194},"Same number, because the coil determines the strength",{"id":1566,"label":2196},"Few or zero washers, because wood has no magnetic domains to align",{"id":1569,"label":2198},"Fewer washers, because wood slightly opposes magnetic fields",[1566],[2201,2202,2203],"Think about what the iron core contributes that the coil alone cannot provide.","Remember what happens to domains inside iron when an external field is applied.","Wood lacks the atomic arrangement that creates magnetic domains. Without domains, there is nothing to align and strengthen the field.",{"correct":2205,"incorrect":2206},"Correct. Wood has no magnetic domains. The coil alone produces only a very weak field, far too feeble to lift washers. The iron core's aligned domains multiply the field strength dramatically.","The iron's domains are essential. Without them, only the coil's weak field remains. Wood provides no domains to align, so the magnetism collapses and the washers stay down.",{"id":2208,"type":1476,"title":2209,"eyebrow":2210,"navLabel":2211},"chapter-79","A Fair Test for the Unknown Metal","Chapter 10","Fair-test practice",{"id":2213,"type":1472,"markdown":2214},"prose-80","You have been asked to find out whether a shiny door handle, a temple bell, or a coin from your grandmother's box is magnetic. It is tempting to wave a magnet at it and shout \"Yes!\" or \"No!\" — but science needs a fair test, one that someone else could repeat and get the same result. In this chapter you will learn to plan, run, and record a reliable magnetic test, just like the experiments in *Curiosity: Textbook of Science for Grade 6, Chapter 4 (Exploring Magnets)*. The secret is to control three things: the magnet itself, the distance, and what lies between the magnet and the object. Skip any of these, and your answer may fool you.\n\nLet us begin with a common trap. A few years ago, a Class 6 student in Pune tested a \"steel\" water bottle and found no attraction. She almost wrote \"non-magnetic\" in her notebook. Then she noticed the paint: thick, rubbery, almost 2 mm deep. When she scraped a tiny spot near the base and touched the magnet to bare metal, the bottle leapt sideways. The paint had acted like a gap. Distance matters enormously in magnetism, and thick coatings can hide the truth. A fair test always reaches the bare surface if possible, or at least notes what sits in between.",{"id":2216,"type":1617,"title":2217,"items":2218},"steps-81","The Fair-Test Method for Magnetism",[2219,2223,2227,2231,2235,2239],{"title":2220,"tag":2221,"text":2222},"Identify the object","Question first","Read any stamp or label. Is it \"SS\" (stainless steel), \"Cu\" (copper), \"Al\" (aluminium)? Ask the owner. Note plating: chrome, nickel, or paint can disguise the core.",{"title":2224,"tag":2225,"text":2226},"Choose a standard magnet","Keep it the same","Use the same bar magnet or neodymium disc for every test in a set. Do not switch halfway, because different magnets have different strengths.",{"title":2228,"tag":2229,"text":2230},"Hold at a fixed distance","Control the gap","Start with the magnet just touching the bare metal. If that is impossible, use a ruler: hold the magnet 5 mm away each time, and record the gap.",{"title":2232,"tag":2233,"text":2234},"Test and classify the pull","Observe carefully","Feel for strong pull, weak tug, or nothing. Does the object move toward the magnet, or does the magnet stick and hang freely?",{"title":2236,"tag":2237,"text":2238},"Check several spots","Repeat and vary","Test top, middle, bottom, edge. Mixed materials or weak temporary magnetism can give different answers in different places.",{"title":2240,"tag":2241,"text":2242},"Record and conclude","Evidence, not guess","Write: object name, surface condition, magnet type, distance, result at each spot. Then decide: magnetic (iron\u002Fsteel\u002Fnickel\u002Fcobalt alloy), weakly magnetic, or non-magnetic.",{"id":2244,"type":1503,"variant":1504,"title":1831,"markdown":2245},"callout-82","This is the most common wrong idea in Indian classrooms. Remember: only iron, nickel, cobalt, and most of their alloys show strong magnetic attraction. Copper pipes, aluminium foil, brass temple lamps, and gold jewellery are metals, yet a magnet ignores them. Calling every shiny object \"metal\" and assuming magnetism is a double error. In your fair-test table, always separate \"metal?\" from \"magnetic?\" — they are different questions.",{"id":2247,"type":1512,"title":2248,"problem":2249,"steps":2250},"worked-example-83","Testing a \"Silver\" Coin from Dadi's Box","Riya finds a round, silvery coin in her grandmother's metal box. There is no stamp. She wants to know if it contains iron or nickel. She has a standard ceramic ferrite bar magnet from her school kit. How should she test it fairly, and what can she conclude?",[2251,2252,2253,2254,2255,2256],"Riya first looks at the coin in sunlight. The colour is silvery-white, not reddish like copper. But colour alone proves nothing; it could be aluminium, nickel, or even stainless steel.","She chooses the bar magnet and decides to use only this magnet for the whole test. She checks its strength on a known iron nail first: the nail snaps to the magnet from 2 cm away. Good, the magnet works.","She holds the bar magnet vertically, 5 mm above the coin's flat face using a ruler as a spacer. Nothing happens. She lowers it until it touches. Still nothing.","She flips the coin and tests the rim, the edge, and the raised lettering. At every spot, silence: no pull, no tug, no stick.","She records: 'Coin, silvery, no stamp. Bar magnet, touch and 5 mm gap. No attraction at any of six spots. Conclusion: coin is non-magnetic. Possible materials: aluminium, a copper-nickel alloy with too little nickel to attract, or a non-magnetic stainless steel.'","Riya remembers that some coins are copper-nickel: the nickel is there for shine, not for magnetism. She does not claim to know the exact metal; she only claims what her evidence supports.",{"id":2258,"type":1553,"itemId":2259,"prompt":2260,"check":2261,"hints":2272,"feedback":2276},"practice-84","magnets.p010","Arjun has an old trophy cup. It looks golden but he suspects brass (non-magnetic) with an iron base (magnetic) for stability. He must test it fairly. Which step in his plan still has a flaw?\n\nStep 1: Ask his father what he remembers about the trophy.\nStep 2: Use a strong neodymium magnet for better sensitivity.\nStep 3: Hold the magnet 5 mm from the outside wall, then at the very bottom rim.\nStep 4: Record whether the magnet sticks, tugs, or ignores the spot.",{"kind":1557,"options":2262,"correct":2271},[2263,2265,2267,2269],{"id":1560,"label":2264},"Step 1: asking his father is unscientific",{"id":1563,"label":2266},"Step 2: switching to a stronger magnet than his classmates use",{"id":1566,"label":2268},"Step 3: not testing the bare surface; paint or lacquer may cover the bottom rim",{"id":1569,"label":2270},"Step 4: he should use numbers, not words like 'tug'",[1566],[2273,2274,2275],"Think about what hides between magnet and metal in a shiny trophy.","If the outside is coated, where might bare metal show?","Fair tests control the surface condition, not just the distance.",{"correct":2277,"incorrect":2278},"Right. Trophy cups are often lacquered or plated. If Arjun never reaches bare metal, a thin coating could block even a strong iron signal from the base. He should find a worn spot or gently scratch a hidden area.","Look again at Step 3. A fair test needs bare metal contact or a known, consistent gap. Paint, lacquer, or plating on a trophy can hide the truth. Arjun must reach the real surface.",{"id":2280,"type":1503,"variant":1637,"title":2281,"markdown":2282},"callout-85","What the fair test cannot do","Your magnetic test identifies magnetism, not chemistry. A strong pull tells you that iron, nickel, or cobalt is present in large amounts, but it does not measure how much. A weak pull might mean a thin iron layer, a poor alloy, or a thick coating adding distance. And \"no pull\" does not prove the absence of every iron atom: some stainless steels contain iron atoms whose domains are locked in a pattern that cancels out magnetism. The fair test is powerful, but it has limits. For a full answer you would need other tools, such as chemical tests or X-ray machines at a metallurgy lab.",{"id":2284,"type":697,"prompt":2285},"reflection-86","Look around your room or kitchen. Pick one object whose magnetic status you genuinely do not know. Before touching a magnet, write down: what you think it is made of, whether you expect it to attract, and why. Then run the six-step fair test. Was your prediction right? If not, which step revealed the surprise?",{"id":2287,"type":1476,"title":2288,"eyebrow":2289,"navLabel":2290},"chapter-87","Check Yourself, and What Comes Next","Chapter 11","Quiz and bridge",{"id":2292,"type":1472,"markdown":2293},"prose-88","You have travelled a long way in this lesson. You began with two surprises at the breakfast table—why a steel spoon stuck to a magnet while a brass bowl did nothing. You met the magnetic family: iron, nickel, cobalt and some of their alloys. You peered inside a chunk of iron and discovered domains, the invisible teams of tiny magnets that normally cancel each other out. You learned that magnetism appears when domains line up, and vanishes when heat, hammering or rough handling scatter them again. You saw why copper and aluminium refuse to stick, even though they are metals. You compared the stubborn stability of a steel spoon with the easy come-and-go magnetism of an iron nail. You understood why a compass needle points north: the Earth itself behaves like a giant magnet, and the needle is just another set of aligned domains. You untangled common mix-ups in Mix-Up Alley, watched electricity organise domains in an electromagnet, and planned a fair test for an unknown metal. Now it is time to check what has stuck—and to see where this road leads next.",{"id":2295,"type":2018,"title":2296,"questions":2297},"quiz-89","Check Yourself: The Magnetism Quiz",[2298,2310,2323,2336,2349,2362,2375,2388],{"itemId":2299,"prompt":2300,"options":2301,"correct":1563,"why":2309},"magnets.q011","A child finds four items in the kitchen: a steel spoon, a copper wire, an aluminium foil and an iron nail. Which ones will stick to a bar magnet?",[2302,2304,2306,2308],{"id":1560,"label":2303},"All four items",{"id":1563,"label":2305},"Only the steel spoon and the iron nail",{"id":1566,"label":2307},"Only the copper wire and the aluminium foil",{"id":1569,"label":1499},"Steel and iron are ferromagnetic materials whose domains can align with an external magnetic field. Copper and aluminium are metals, but they are not ferromagnetic: their electron arrangements do not form stable domains that respond strongly to a bar magnet. This is why they do not stick.",{"itemId":2311,"prompt":2312,"options":2313,"correct":1563,"why":2322},"magnets.q012","A magnet is heated in a flame until it is too hot to touch. After cooling, it no longer attracts iron filings. What happened to the domains?",[2314,2316,2318,2320],{"id":1560,"label":2315},"The domains melted and drained out of the metal",{"id":1563,"label":2317},"Thermal vibrations shook the domains out of alignment, and they settled randomly after cooling",{"id":1566,"label":2319},"The north poles turned into south poles",{"id":1569,"label":2321},"The domains were chemically destroyed by oxidation","Heat adds energy to atoms, making them vibrate vigorously. This vibration randomises the domain alignment. When the magnet cools, the domains settle in random directions unless a strong external field re-aligns them. The domains still exist; they are simply pointing every which way.",{"itemId":2324,"prompt":2325,"options":2326,"correct":1566,"why":2335},"magnets.q013","Rahul says, 'All metals are attracted to magnets because metals contain iron.' Is this statement correct?",[2327,2329,2331,2333],{"id":1560,"label":2328},"Yes, all metals contain at least traces of iron",{"id":1563,"label":2330},"Yes, magnetism is a general property of all metals",{"id":1566,"label":2332},"No, only ferromagnetic metals like iron, nickel and cobalt are strongly attracted",{"id":1569,"label":2334},"No, no metals are attracted to magnets","This is a common misconception. Most metals—aluminium, copper, gold, silver, lead—are not ferromagnetic. They do not contain iron, and they do not form the aligned domains needed for strong attraction. Only iron, nickel, cobalt and certain alloys show this behaviour.",{"itemId":2337,"prompt":2338,"options":2339,"correct":1563,"why":2348},"magnets.q014","A steel paper clip and an iron nail are both magnetised by stroking with a strong magnet. Which one is more likely to stay magnetised for weeks, and why?",[2340,2342,2344,2346],{"id":1560,"label":2341},"The iron nail, because pure iron holds alignment better",{"id":1563,"label":2343},"The steel paper clip, because steel's domains are harder to shift once aligned",{"id":1566,"label":2345},"Both stay magnetised equally long",{"id":1569,"label":2347},"Neither stays magnetised more than a day","Steel is an alloy of iron with carbon. The carbon atoms disturb the regular crystal structure, making it harder for domains to rotate back to random directions. Iron is softer magnetically: its domains re-randomise more easily. This is why steel makes good permanent magnets and iron is better for temporary or electromagnet cores.",{"itemId":2350,"prompt":2351,"options":2352,"correct":1566,"why":2361},"magnets.q015","Which of these steps is essential for a fair test to find whether an unknown metal rod is magnetic?",[2353,2355,2357,2359],{"id":1560,"label":2354},"Test it near an open flame to see if heat changes its magnetism",{"id":1563,"label":2356},"Rub it with silk first to give it an electric charge",{"id":1566,"label":2358},"Bring the same magnet slowly to the rod, observe if attraction occurs, repeat with other known metals for comparison",{"id":1569,"label":2360},"Drop it from a height and see if it points north when it lands","A fair test changes only the material being tested while keeping everything else the same: the same magnet, the same distance, the same temperature. Comparing the unknown rod with known magnetic and non-magnetic samples under identical conditions lets you draw a reliable conclusion.",{"itemId":2363,"prompt":2364,"options":2365,"correct":1563,"why":2374},"magnets.q016","An electromagnet is made by coiling copper wire around an iron nail and connecting the ends to a battery. What happens inside the iron when current flows?",[2366,2368,2370,2372],{"id":1560,"label":2367},"The copper wire becomes magnetic and the iron remains unchanged",{"id":1563,"label":2369},"Electric current creates a magnetic field that aligns the domains in the iron, making the nail magnetic",{"id":1566,"label":2371},"The battery's chemicals leak into the iron and make it magnetic",{"id":1569,"label":2373},"The iron nail becomes electrically charged and therefore magnetic","Moving electric charge—current—creates a magnetic field around the wire. This field is weak by itself, but inside the iron core it is strong enough to align the iron's domains. The aligned domains multiply the effect, making the electromagnet much stronger than the coil alone. When the current stops, the domains mostly randomise again.",{"itemId":2376,"prompt":2377,"options":2378,"correct":1563,"why":2387},"magnets.q017","Why does a freely suspended bar magnet or compass needle turn to point north-south?",[2379,2381,2383,2385],{"id":1560,"label":2380},"Because the magnet is attracted only by the North Pole star",{"id":1563,"label":2382},"Because the Earth acts like a giant magnet with a magnetic south pole near geographic north, attracting the needle's north pole",{"id":1566,"label":2384},"Because wind patterns at the Earth's surface push the needle",{"id":1569,"label":2386},"Because the needle is made of iron which naturally points north","The Earth has a magnetic field generated by movements in its molten iron core. The geographic North Pole is near the Earth's magnetic south pole. A compass needle is a small bar magnet; like poles repel and opposite poles attract. Therefore the needle's north-seeking pole is attracted toward Earth's magnetic south, which lies near geographic north.",{"itemId":2389,"prompt":2390,"options":2391,"correct":1563,"why":2400},"magnets.q018","Arrange the following from smallest to largest: one magnetic domain inside iron, a fridge magnet, the Earth's magnetic field region.",[2392,2394,2396,2398],{"id":1560,"label":2393},"Fridge magnet, domain, Earth's field",{"id":1563,"label":2395},"Domain, fridge magnet, Earth's field",{"id":1566,"label":2397},"Earth's field, fridge magnet, domain",{"id":1569,"label":2399},"Domain, Earth's field, fridge magnet","A magnetic domain is microscopic—roughly 0.001 to 0.1 millimetres across in iron. A fridge magnet is a few centimetres long, visible and holdable. The Earth's magnetic field extends thousands of kilometres into space, forming the magnetosphere. The scale spans roughly ten orders of magnitude from domain to planetary field.",{"id":2402,"type":1913,"title":2403,"scale":2404,"rungs":2405},"ladder-90","Sizes in Magnetism: A Powers-of-Ten Ladder","log",[2406,2410,2414,2417,2420,2424,2428],{"label":2407,"value":2408,"display":2409},"One magnetic domain in iron",0.000001,"~1 micrometre",{"label":2411,"value":2412,"display":2413},"Finest iron filing that shows a field pattern",0.01,"~10 micrometres",{"label":2415,"value":44,"display":2416},"Visible iron filing cluster on paper","~1 millimetre",{"label":2418,"value":472,"display":2419},"Small bar magnet from a school kit","~5 centimetres",{"label":2421,"value":2422,"display":2423},"Laboratory electromagnet coil",500,"~0.5 metre",{"label":2425,"value":2426,"display":2427},"MRI scanner magnet (hospital)",3000,"~3 metres",{"label":2429,"value":2430,"display":2431},"Earth's magnetosphere tail length",1000000000,"~1 million km",{"id":2433,"type":1472,"markdown":2434},"prose-91","Where does this understanding take you next? At the depth you have just completed—'understand'—you have worked with domains as a labelled model. You have treated domains as tiny compass-teams inside iron, and that model explains almost everything you meet in daily life: why heating destroys a magnet, why steel outlasts iron, why electromagnets need a core, why Earth steers a compass. The model is powerful and practical. But it is still a model. It does not tell you why domains exist in the first place, or why iron, nickel and cobalt are special. The next depth, 'deepen,' goes inside the atom. There you will meet electron spin, a quantum property that acts like a tiny built-in magnet on every electron. You will learn that in most materials, electrons pair up so their spins cancel. In iron-group elements, unpaired electrons cooperate across thousands of atomic spacings to create domains. You will also see how moving magnets generate electricity—the discovery that Faraday and others built into generators, transformers and the national grid. Electricity making magnets, magnets making electricity: these two processes are the paired heartbeat of modern technology, from the motor in your ceiling fan to the windings in an ISRO satellite's momentum wheel. If you have understood domains, you are ready for that next step.",{"id":2436,"type":1503,"variant":2437,"title":2438,"markdown":2439},"callout-92","careful","A Model's Boundary","The domain model you have learned is deliberately simplified. We drew domains as neat blocks with arrows, all pointing the same way inside one domain. Real domains have irregular shapes, and their boundaries—called domain walls—move gradually, not all at once. At very small scales, near absolute zero or in ultra-thin films, domains behave even differently. For Class 5–7 explanations and everyday predictions, the block-and-arrow model is excellent. For designing next-generation computer memory or explaining why one alloy beats another, scientists use quantum mechanics. Always know the boundary of your model: it keeps you accurate without making you unnecessarily complex.",{"id":2441,"type":1512,"title":2442,"problem":2443,"steps":2444},"worked-example-93","Predict and Explain: The Unknown Alloy","An engineer has a new alloy of iron, nickel and cobalt. She wants to know if it will make a good permanent magnet for an electric scooter motor. Using only what you know about domains, predict two properties she should test and explain what the results would tell her.",[2445,2446,2447,2448,2449],"Test 1: Does it become strongly magnetised when placed in a strong field?","If yes, its domains align easily under an external field. This tells her the alloy is ferromagnetic and could work as a magnet.","Test 2: After the external field is removed, does it keep most of its magnetism?","If yes, its domains stay aligned. This tells her the alloy has high coercivity—domains resist randomising after alignment. A motor magnet needs this so it does not weaken during use.","If the alloy passes both tests, it is a candidate permanent magnet. If it magnetises easily but loses magnetism quickly, it is more like soft iron—useful for electromagnet cores, not for permanent motors.",{"id":2451,"type":1581,"title":2452,"points":2453},"summary-94","What Stuck? The Core Ideas of This Lesson",[2454,2455,2456,2457,2458,2459,2460,2461,2462,2463,2464],"Magnetism is not magic; it is the organised behaviour of countless tiny domains inside certain materials.","A domain is a region inside a ferromagnetic material where atomic magnets line up; neighbouring domains may point differently, cancelling the overall effect.","Iron, nickel, cobalt and some of their alloys are ferromagnetic: their domains can align with an external field and stay aligned to some degree.","Copper, aluminium, wood, plastic and most other materials lack this domain behaviour; they are non-magnetic in everyday conditions.","Magnetism appears when domains align; it weakens when heat, hammering or dropping scatters them back to random directions.","Steel keeps magnetism longer than pure iron because carbon in steel pins domains in place, making them harder to randomise.","The Earth acts as a giant magnet because of electric currents in its molten iron core; a compass needle is simply a set of aligned domains responding to Earth's field.","An electromagnet uses electric current to create a magnetic field that aligns domains in an iron core; turning off the current lets domains randomise again.","A fair test changes only one variable at a time and compares the unknown sample with known samples under identical conditions.","The domain model explains daily magnetic phenomena well, but deeper explanations require quantum mechanics and electron spin.","The future of technology—from MRI machines to maglev trains and ISRO missions—depends on understanding and controlling magnetism at every level.",{"id":2466,"type":2467,"title":2468,"terms":2469},"glossary-95","glossary","Key Terms from This Lesson",[2470,2474,2478,2482,2486,2490,2494,2498,2501,2505,2509,2512,2516,2520],{"term":2471,"meaning":2472,"example":2473},"Magnet","An object that produces a magnetic field and can attract or repel other magnetic materials.","A bar magnet from a school science kit.",{"term":2475,"meaning":2476,"example":2477},"Magnetic pole","A region of a magnet where the magnetic effect is strongest; every magnet has a north pole and a south pole.","The ends of a bar magnet where iron filings cluster most thickly.",{"term":2479,"meaning":2480,"example":2481},"Attraction","The pulling force between opposite magnetic poles or between a magnet and a ferromagnetic material.","A magnet pulling an iron nail toward it.",{"term":2483,"meaning":2484,"example":2485},"Repulsion","The pushing force between like magnetic poles (north-north or south-south).","Two bar magnets with north poles facing each other sliding apart.",{"term":2487,"meaning":2488,"example":2489},"Ferromagnetic material","A material, such as iron, nickel or cobalt, whose atoms can form domains that align strongly with a magnetic field.","Iron filings that jump toward a magnet.",{"term":2491,"meaning":2492,"example":2493},"Non-magnetic material","A material that does not form aligning domains and shows negligible attraction to magnets under ordinary conditions.","A copper coin that does not respond to a fridge magnet.",{"term":2495,"meaning":2496,"example":2497},"Magnetic domain","A microscopic region within a ferromagnetic material where atomic magnets are aligned parallel; the unit of the labelled model used in this lesson.","A domain in iron roughly 0.001 to 0.1 millimetres across.",{"term":1695,"meaning":2499,"example":2500},"The process by which magnetic domains rotate to point in the same direction, producing a net magnetic field.","Stroking an iron nail with a strong bar magnet to make it magnetic.",{"term":2502,"meaning":2503,"example":2504},"Permanent magnet","A material that retains aligned domains and therefore its magnetism for a long time after the external field is removed.","A steel paper clip that stays magnetic for weeks.",{"term":2506,"meaning":2507,"example":2508},"Temporary magnet","A material that aligns its domains only while an external field is present and loses most magnetism afterward.","An iron nail that attracts filings only while touched to a strong magnet.",{"term":2138,"meaning":2510,"example":2511},"A magnet created by passing electric current through a coil, often with an iron core to strengthen the effect by domain alignment.","A crane in a scrapyard that lifts iron, then drops it when the current stops.",{"term":2513,"meaning":2514,"example":2515},"Magnetic field","The region around a magnet where magnetic forces can be detected; visualised by iron filing patterns or compass deflections.","The space around a bar magnet where a compass needle turns.",{"term":2517,"meaning":2518,"example":2519},"Compass","A small magnet pivoted so it can rotate freely, aligning with Earth's magnetic field to indicate direction.","A hiking compass pointing toward geographic north.",{"term":2521,"meaning":2522,"example":2523},"Fair test","An investigation in which only one variable is changed at a time, with all other conditions kept constant for reliable comparison.","Testing unknown and known metals with the same magnet at the same distance.",{"id":2525,"type":2526,"sourceIds":2527},"sources-96","sources",[2528,2529],"magnets-ncert-curiosity-6-ch4","angles-wiki-degree",[2528,2529],"needs_review",{"generatedBy":2533,"notes":2534},"claude-code","generated from work item wi-61bfa1ee (11 chapters)","d684ef1a0c1fe00fc5c9e9bc381e6263930ecb7506d6a1617bdc2c4471d405b5",{},{"state":6,"reviewer":2538,"selfReview":2539,"reviewedAt":2540,"method":806},"curator",false,"2026-09-21T04:52:13.354622+00:00","generation-19f885ad-fe89-48be-9528-20ae7eee520b",[2543,2551],{"id":2529,"title":2544,"publisher":2545,"url":2546,"kind":2547,"accessed":2548,"usage":2549,"verification":2550},"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":2528,"title":2552,"publisher":2553,"url":2554,"kind":2555,"accessed":2556,"usage":2557,"verification":2550},"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."]