[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"content-index":3,"content-questions:magnets":1418},{"release":4,"domains":9,"concepts":110,"edges":1306,"journeys":1415,"sources":1416,"glossary":1417,"lean":147},{"releaseId":5,"mode":6,"createdAt":7,"manifestHash":8},"remote-muamu4zn","approved","2026-09-21T02:34:59.651Z","1b4a7ed3a788279682beba6616860611bf9cc017fed7c62d86399a5fe0e1502e",[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.",[111,179,239,286,339,389,438,488,540,587,637,689,738,788,811,860,912,963,1013,1060,1109,1161,1211,1259],{"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":807},"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",[801,803],{"depth":142,"revision":44,"title":790,"subtitle":437,"summary":790,"estimatedMinutes":178,"reviewed":147,"reviewMethod":802},"per_lesson",{"depth":150,"revision":44,"title":804,"subtitle":805,"summary":806,"estimatedMinutes":178,"reviewed":147,"reviewMethod":802},"How Magnets Pull: Poles, Materials, and Fields","A closer look at why magnets attract, repel, and turn some metals magnetic","This lesson explains why every magnet has two poles, why cutting a magnet still leaves two poles, and how like and unlike poles behave. It also explores magnetic materials, temporary and permanent magnets, and the invisible magnetic field.",{"count":808,"sections":66,"levels":809},52,{"foundation":810,"core":337,"stretch":787,"challenge":385},14,{"id":812,"slug":812,"title":813,"question":814,"promise":815,"domains":816,"areas":817,"keywords":818,"status":139,"layers":837,"questionBank":858},"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],[819,458,820,821,754,822,823,824,825,826,827,828,829,830,831,832,833,834,835,836],"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",[838,842,846,850,854],{"depth":142,"revision":44,"title":839,"subtitle":840,"summary":841,"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":843,"subtitle":844,"summary":845,"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":847,"subtitle":848,"summary":849,"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":851,"subtitle":852,"summary":853,"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":855,"subtitle":856,"summary":857,"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":859},{"foundation":178,"core":338,"stretch":284,"challenge":174},{"id":861,"slug":861,"title":862,"question":863,"promise":864,"domains":865,"areas":866,"keywords":867,"status":139,"layers":887,"questionBank":908},"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],[861,868,869,870,871,872,873,874,875,876,877,878,879,880,881,882,883,884,885,886],"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",[888,892,896,900,904],{"depth":142,"revision":44,"title":889,"subtitle":890,"summary":891,"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":893,"subtitle":894,"summary":895,"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":897,"subtitle":898,"summary":899,"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":901,"subtitle":902,"summary":903,"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":905,"subtitle":906,"summary":907,"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":909,"sections":233,"levels":910},81,{"foundation":178,"core":911,"stretch":387,"challenge":233},33,{"id":913,"slug":913,"title":914,"question":915,"promise":916,"domains":917,"areas":918,"keywords":919,"status":139,"layers":939,"questionBank":960},"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],[920,921,922,923,924,925,926,927,928,929,930,931,501,932,933,934,935,936,937,938],"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",[940,944,948,952,956],{"depth":142,"revision":44,"title":941,"subtitle":942,"summary":943,"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":945,"subtitle":946,"summary":947,"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":949,"subtitle":950,"summary":951,"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":953,"subtitle":954,"summary":955,"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":957,"subtitle":958,"summary":959,"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":961,"sections":233,"levels":962},83,{"foundation":235,"core":338,"stretch":176,"challenge":238},{"id":964,"slug":964,"title":965,"question":966,"promise":967,"domains":968,"areas":969,"keywords":970,"status":139,"layers":990,"questionBank":1011},"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],[971,972,973,974,975,976,977,978,979,980,981,982,983,984,985,986,500,987,988,989],"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",[991,995,999,1003,1007],{"depth":142,"revision":44,"title":992,"subtitle":993,"summary":994,"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":996,"subtitle":997,"summary":998,"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":1000,"subtitle":1001,"summary":1002,"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":1004,"subtitle":1005,"summary":1006,"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":1008,"subtitle":1009,"summary":1010,"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":1012},{"foundation":284,"core":636,"stretch":786,"challenge":385},{"id":1014,"slug":1014,"title":1015,"question":1016,"promise":1017,"domains":1018,"areas":1019,"keywords":1020,"status":139,"layers":1037,"questionBank":1058},"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],[1021,1022,1023,1024,1025,1026,1027,1028,1029,1030,551,1031,1032,1033,1034,1035,1036],"moon","phases","new moon","full moon","crescent","gibbous","waxing","waning","lunar month","synodic","tithi","Purnima","Amavasya","terminator","earthshine","far side",[1038,1042,1046,1050,1054],{"depth":142,"revision":44,"title":1039,"subtitle":1040,"summary":1041,"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":1043,"subtitle":1044,"summary":1045,"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":1047,"subtitle":1048,"summary":1049,"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":1051,"subtitle":1052,"summary":1053,"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":1055,"subtitle":1056,"summary":1057,"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":1059},{"foundation":284,"core":387,"stretch":337,"challenge":810},{"id":1061,"slug":1061,"title":1062,"question":1063,"promise":1064,"domains":1065,"areas":1066,"keywords":1067,"status":139,"layers":1086,"questionBank":1107},"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],[1068,1069,1070,1071,1072,609,1073,1074,604,1075,1076,1077,1078,1079,1080,1081,1082,1083,1084,1085],"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",[1087,1091,1095,1099,1103],{"depth":142,"revision":44,"title":1088,"subtitle":1089,"summary":1090,"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":1092,"subtitle":1093,"summary":1094,"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":1096,"subtitle":1097,"summary":1098,"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":1100,"subtitle":1101,"summary":1102,"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":1104,"subtitle":1105,"summary":1106,"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":1108},{"foundation":235,"core":236,"stretch":176,"challenge":233},{"id":1110,"slug":1110,"title":1111,"question":1112,"promise":1113,"domains":1114,"areas":1115,"keywords":1116,"status":139,"layers":1137,"questionBank":1158},"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],[1117,1118,1119,1120,1121,1122,1123,1124,1125,1126,1127,1128,1129,1130,1131,1132,1133,1134,1135,1136],"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",[1138,1142,1146,1150,1154],{"depth":142,"revision":44,"title":1139,"subtitle":1140,"summary":1141,"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":1143,"subtitle":1144,"summary":1145,"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":1147,"subtitle":1148,"summary":1149,"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":1151,"subtitle":1152,"summary":1153,"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":1155,"subtitle":1156,"summary":1157,"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":1159,"sections":385,"levels":1160},85,{"foundation":237,"core":212,"stretch":284,"challenge":174},{"id":1162,"slug":1162,"title":1163,"question":1164,"promise":1165,"domains":1166,"areas":1167,"keywords":1168,"status":139,"layers":1188,"questionBank":1209},"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],[1169,1170,1171,1172,1173,1174,1175,708,1176,1177,1178,1179,1180,1181,1182,1183,1184,1185,1186,1187],"polygon","triangle","quadrilateral","circle","diagonals","cube","cuboid","pyramid","faces edges vertices","net","views","line symmetry","rotational symmetry","Euler","Platonic solids","tangram","tessellation","2D","3D",[1189,1193,1197,1201,1205],{"depth":142,"revision":44,"title":1190,"subtitle":1191,"summary":1192,"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":1194,"subtitle":1195,"summary":1196,"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":1198,"subtitle":1199,"summary":1200,"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":1202,"subtitle":1203,"summary":1204,"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":1206,"subtitle":1207,"summary":1208,"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":1210},{"foundation":284,"core":636,"stretch":284,"challenge":238},{"id":1212,"slug":1212,"title":52,"question":1213,"promise":1214,"domains":1215,"areas":1216,"keywords":1217,"status":139,"layers":1236,"questionBank":1257},"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],[1212,1218,1219,1220,1221,1222,1223,1224,1225,1226,1227,1228,1229,1230,1231,1232,1233,1234,1235],"vibration","wave","pitch","frequency","amplitude","loudness","decibel","echo","medium","ultrasound","hertz","eardrum","resonance","speed of sound","noise","music","sonar","vacuum",[1237,1241,1245,1249,1253],{"depth":142,"revision":44,"title":1238,"subtitle":1239,"summary":1240,"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":1242,"subtitle":1243,"summary":1244,"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":1246,"subtitle":1247,"summary":1248,"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":1250,"subtitle":1251,"summary":1252,"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":1254,"subtitle":1255,"summary":1256,"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":1258},{"foundation":388,"core":911,"stretch":337,"challenge":233},{"id":560,"slug":560,"title":1260,"question":1261,"promise":1262,"domains":1263,"areas":1264,"keywords":1265,"status":139,"layers":1282,"questionBank":1303},"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],[1266,1267,1268,1269,1270,1271,1272,541,1273,1274,1275,1276,1277,1278,1279,1280,1281],"tide","high tide","low tide","spring tide","neap tide","tidal range","bulge","Moon","Sun","tidal bore","estuary","tide table","coast","fishing","Chandipur","Hooghly",[1283,1287,1291,1295,1299],{"depth":142,"revision":44,"title":1284,"subtitle":1285,"summary":1286,"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":1288,"subtitle":1289,"summary":1290,"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":1292,"subtitle":1293,"summary":1294,"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":1296,"subtitle":1297,"summary":1298,"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":1300,"subtitle":1301,"summary":1302,"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":1304,"sections":385,"levels":1305},71,{"foundation":786,"core":283,"stretch":284,"challenge":174},[1307,1310,1312,1315,1317,1319,1321,1323,1325,1327,1329,1331,1334,1337,1339,1341,1343,1345,1347,1349,1351,1353,1355,1357,1359,1361,1363,1365,1367,1369,1371,1373,1375,1377,1379,1381,1383,1385,1387,1389,1391,1393,1395,1397,1399,1401,1403,1405,1407,1409,1411,1413],{"from":913,"to":489,"relation":1308,"reason":1309},"helps_understand","Place value is what makes column addition, carrying and long division work.",{"from":913,"to":287,"relation":1308,"reason":1311},"Reading, comparing and rounding numbers comes first when you sort data and round a mean.",{"from":913,"to":861,"relation":1313,"reason":1314},"related_to","Place-value charts are full of patterns: each place is ten times the one to its right.",{"from":1110,"to":489,"relation":1308,"reason":1316},"Commutative, associative and distributive properties are the shortcuts behind fast, accurate calculation.",{"from":1110,"to":964,"relation":1308,"reason":1318},"The distributive property explains why multiplication is done before addition and how brackets change a result.",{"from":1110,"to":861,"relation":1313,"reason":1320},"Many number patterns — like the sum of consecutive odd numbers — are properties of numbers in disguise.",{"from":489,"to":964,"relation":1308,"reason":1322},"Once each operation is reliable, the next question is which one to do first when several appear together.",{"from":489,"to":1061,"relation":1308,"reason":1324},"Testing whether a number is prime is just careful division: does anything divide it exactly?",{"from":489,"to":287,"relation":1308,"reason":1326},"Finding a mean means adding every value and dividing by how many there are.",{"from":964,"to":861,"relation":1313,"reason":1328},"A pattern rule such as 3 × n + 1 is an expression — you need the order of operations to use it.",{"from":1061,"to":588,"relation":1308,"reason":1330},"Prime factorisation is the fastest route to both the HCF and the LCM.",{"from":1061,"to":861,"relation":1332,"reason":1333},"contrasts_with","Primes famously refuse to follow a simple pattern, unlike even numbers, squares or multiples.",{"from":588,"to":861,"relation":1335,"reason":1336},"applied_in","Two repeating cycles line up again after their LCM — the pattern behind blinking lights and bus timetables.",{"from":588,"to":1162,"relation":1335,"reason":1338},"The largest square tile that fits a rectangular floor exactly has a side equal to the HCF of its length and width.",{"from":861,"to":1162,"relation":1313,"reason":1340},"Growing shape patterns — matchstick squares, dot triangles — are geometry and number at the same time.",{"from":1162,"to":739,"relation":1313,"reason":1342},"Every polygon is built from line segments, and its sides can be parallel or perpendicular.",{"from":1162,"to":180,"relation":1313,"reason":1344},"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":1308,"reason":1346},"An angle is two rays that share an end point; intersecting lines make angle pairs.",{"from":739,"to":812,"relation":1308,"reason":1348},"Constructions rely on drawing straight lines, perpendiculars and bisectors accurately.",{"from":180,"to":812,"relation":1308,"reason":1350},"Knowing angle types and pairs tells you what you are measuring and checks if your construction is sensible.",{"from":180,"to":287,"relation":1335,"reason":1352},"In a pie chart each slice's angle shows a share of the data: 360° stands for the whole.",{"from":812,"to":1162,"relation":1335,"reason":1354},"Drawing accurate triangles, squares and regular polygons needs measured or constructed angles.",{"from":287,"to":390,"relation":1335,"reason":1356},"A family's monthly electricity use varies; the mean, median and range of a year of bills show what is typical.",{"from":913,"to":390,"relation":1335,"reason":1358},"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":1335,"reason":1360},"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":1335,"reason":1362},"A generator's coil turns through 360° every cycle — 50 full turns a second on India's 50 Hz supply.",{"from":1061,"to":390,"relation":1335,"reason":1364},"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":1308,"reason":1366},"An eclipse is a shadow, and shadows need light that travels in straight lines.",{"from":690,"to":1014,"relation":1308,"reason":1368},"The Moon has no light of its own: we see the half of it the Sun is lighting.",{"from":690,"to":112,"relation":1335,"reason":1370},"The eye is a lens, a screen and a shutter — optics built out of living tissue.",{"from":690,"to":1212,"relation":1332,"reason":1372},"Both travel as waves and carry energy, but light needs no material and races a million times faster than sound.",{"from":1212,"to":112,"relation":1335,"reason":1374},"The ear turns shaking air into signals a nerve can carry: a drum, three tiny bones and a spiral of fluid.",{"from":541,"to":1014,"relation":1308,"reason":1376},"Gravity is what keeps the Moon in the orbit that produces the monthly cycle of phases.",{"from":541,"to":560,"relation":1308,"reason":1378},"Tides are gravity made visible: the Moon pulls the near ocean harder than the far ocean.",{"from":541,"to":340,"relation":1308,"reason":1380},"Eclipses happen only because the Sun, Earth and Moon move on fixed gravitational paths we can predict.",{"from":1014,"to":340,"relation":1308,"reason":1382},"Eclipses can only happen at new moon or full moon — the two phases where the three bodies line up.",{"from":1014,"to":560,"relation":1313,"reason":1384},"Spring and neap tides follow the phases: the biggest tides come at new and full moon.",{"from":112,"to":240,"relation":1308,"reason":1386},"Once you know where each organ sits, you can follow how they pass work to each other.",{"from":240,"to":541,"relation":1313,"reason":1388},"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":1308,"reason":1390},"The empires that grew out of the voyages shaped the constitution and the freedoms India wrote for itself afterwards.",{"from":439,"to":560,"relation":1335,"reason":1392},"Sailing ships left harbour on the tide, and monsoon winds and currents set the whole calendar of Indian Ocean trade.",{"from":439,"to":1014,"relation":1335,"reason":1394},"Before clocks and satellites, the Moon and stars were how a navigator knew where they were.",{"from":638,"to":287,"relation":1335,"reason":1396},"A census, an election result and a budget are all data: counted, summarised and argued over.",{"from":638,"to":913,"relation":1335,"reason":1398},"Election results and budgets are read in lakhs and crores — place value with real consequences.",{"from":690,"to":390,"relation":1313,"reason":1400},"A bulb, an LED and a solar panel are all conversions between electricity and light.",{"from":1212,"to":390,"relation":1313,"reason":1402},"Microphones and speakers turn sound into current and current back into sound.",{"from":439,"to":1162,"relation":1335,"reason":1404},"Maps, globes and navigation are geometry: a round Earth flattened onto paper without lying too much.",{"from":340,"to":180,"relation":1335,"reason":1406},"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":1335,"reason":1408},"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":1335,"reason":1410},"Heart rate, height and lung capacity across a class are real data to collect, average and compare.",{"from":541,"to":489,"relation":1335,"reason":1412},"Weight on another world is your mass times that world's gravity — multiplication with an astonishing answer.",{"from":240,"to":287,"relation":1335,"reason":1414},"Pulse and breathing rate before and after exercise are real class data to average, compare and graph.",[],[],[],{"bank":1419,"contentHash":2501,"dependencyHashes":2502,"releaseId":2503},{"schemaVersion":44,"conceptId":789,"revision":44,"title":790,"intro":790,"sections":1420,"questions":1429,"sourceIds":2493,"reviewStatus":2497,"authoring":2498},[1421,1425],{"id":1422,"title":1423,"description":1424},"core","Core practice","Practice for this topic.",{"id":1426,"title":1427,"description":1428},"stretch","Stretch","Harder practice for this topic.",[1430,1458,1480,1492,1512,1534,1556,1578,1599,1621,1643,1665,1685,1706,1728,1749,1757,1777,1800,1821,1842,1864,1885,1907,1920,1941,1962,1984,2005,2026,2047,2064,2085,2106,2128,2150,2170,2193,2207,2226,2247,2270,2293,2315,2337,2361,2372,2391,2412,2426,2449,2471],{"id":1431,"section":1422,"level":1432,"prompt":1433,"check":1434,"hints":1450,"solution":1454,"skills":1455},"magnets.q001","foundation","A child tests four objects with a bar magnet: an iron nail, a copper coin, aluminium foil, and a wooden pencil. Which object is most likely to stick to the magnet?",{"kind":1435,"options":1436,"correct":1449},"choice",[1437,1440,1443,1446],{"id":1438,"label":1439},"a","Iron nail",{"id":1441,"label":1442},"b","Copper coin",{"id":1444,"label":1445},"c","Aluminium foil",{"id":1447,"label":1448},"d","Wooden pencil",[1438],[1451,1452,1453],"Magnetic materials contain iron, nickel or cobalt.","Copper and aluminium are metals but are not magnetic.","Wood is not a metal.","A bar magnet attracts materials such as iron, nickel, cobalt and steel. An iron nail contains iron, so it sticks to the magnet. Copper and aluminium are metals, but they are not magnetic. Wood is non-magnetic. Answer: Iron nail.",[1456,1457],"Identifying magnetic materials","Testing materials with a magnet",{"id":1459,"section":1422,"level":1432,"prompt":1460,"check":1461,"hints":1472,"solution":1476,"skills":1477},"magnets.q002","What happens when the north pole of one bar magnet is brought close to the north pole of another bar magnet?",{"kind":1435,"options":1462,"correct":1471},[1463,1465,1467,1469],{"id":1438,"label":1464},"They attract strongly",{"id":1441,"label":1466},"They repel each other",{"id":1444,"label":1468},"They neither attract nor repel",{"id":1447,"label":1470},"They stick only if one magnet is bigger",[1441],[1473,1474,1475],"Like poles behave in the same way.","North-north are like poles.","Unlike poles attract; like poles repel.","Every magnet has two poles: north and south. Like poles, such as north-north or south-south, push each other away, so they repel. Unlike poles, such as north-south, pull together. Answer: They repel each other.",[1478,1479],"Poles of a magnet","Attraction and repulsion",{"id":1481,"section":1422,"level":1432,"prompt":1482,"check":1483,"hints":1485,"solution":1489,"skills":1490},"magnets.q003","How many poles does a bar magnet have?",{"kind":1484,"answer":66,"tolerance":14},"number",[1486,1487,1488],"A pole is where the magnetic force is strongest.","One pole is called north and the other is called south.","Even if you break a magnet, each piece still has both poles.","A bar magnet has two poles: a north pole and a south pole. The magnetic force is strongest near these two ends. Answer: 2.",[1478,1491],"Magnetic force",{"id":1493,"section":1422,"level":1432,"prompt":1494,"check":1495,"hints":1504,"solution":1508,"skills":1509},"magnets.q004","Name one metal that is NOT attracted to a magnet.",{"kind":1496,"accept":1497},"text",[1498,1499,1500,1501,1502,1503],"copper","Copper","aluminium","Aluminium","aluminum","Aluminum",[1505,1506,1507],"Iron, nickel and cobalt are magnetic metals.","Think of metals used in wires or kitchen foil.","Copper and aluminium are metals but do not stick to a magnet.","Not all metals are magnetic. Copper and aluminium are common metals that a magnet does not attract. Answer: copper or aluminium.",[1510,1511],"Non-magnetic metals","Magnetic materials",{"id":1513,"section":1422,"level":1432,"prompt":1514,"check":1515,"hints":1526,"solution":1530,"skills":1531},"magnets.q005","A freely suspended bar magnet is allowed to turn. In which direction does it finally come to rest?",{"kind":1435,"options":1516,"correct":1525},[1517,1519,1521,1523],{"id":1438,"label":1518},"East-west",{"id":1441,"label":1520},"North-south",{"id":1444,"label":1522},"Up-down",{"id":1447,"label":1524},"Any direction",[1441],[1527,1528,1529],"Earth behaves like a giant magnet.","A compass needle is a small magnet.","A magnet's north pole points toward Earth's magnetic north.","A freely moving magnet lines up with Earth's magnetic field. One end points north and the other points south, so it rests in the north-south direction. This is how a compass works. Answer: North-south.",[1532,1533],"Earth as a magnet","Compass directions",{"id":1535,"section":1422,"level":1432,"prompt":1536,"check":1537,"hints":1548,"solution":1552,"skills":1553},"magnets.q006","In an activity, iron filings are sprinkled around a bar magnet. What do the curved lines of iron filings show?",{"kind":1435,"options":1538,"correct":1547},[1539,1541,1543,1545],{"id":1438,"label":1540},"The colour of the magnet",{"id":1441,"label":1542},"The magnetic field around the magnet",{"id":1444,"label":1544},"The weight of the magnet",{"id":1447,"label":1546},"That iron filings are wet",[1441],[1549,1550,1551],"The region around a magnet where it can attract iron is its magnetic field.","Iron filings line up along the field.","The pattern is strongest near the poles.","Iron filings arrange themselves along the invisible magnetic field lines around the magnet. The pattern shows the magnetic field, and it is strongest near the poles. Answer: The magnetic field around the magnet.",[1554,1555],"Magnetic field","Iron filings pattern",{"id":1557,"section":1426,"level":1432,"prompt":1558,"check":1559,"hints":1570,"solution":1574,"skills":1575},"magnets.q007","Ravi says: \"A bigger magnet is always stronger than a smaller magnet.\" Is this statement correct?",{"kind":1435,"options":1560,"correct":1569},[1561,1563,1565,1567],{"id":1438,"label":1562},"Yes, size is the only thing that decides strength",{"id":1441,"label":1564},"No, strength depends on material and how it is magnetised, not only size",{"id":1444,"label":1566},"Yes, all big magnets are equally strong",{"id":1447,"label":1568},"No, smaller magnets can never be strong",[1441],[1571,1572,1573],"Think of a large piece of iron that is not magnetised.","A small magnet made of a strong magnetic material can be very strong.","Strength depends on the magnetic material and how it is made.","Size alone does not decide a magnet's strength. A large piece of unmagnetised iron has no noticeable magnetic force, while a small magnet made of a strong magnetic material can lift many paper clips. Strength depends on material, shape and magnetisation. Answer: No, strength depends on material and how it is magnetised, not only size.",[1576,1577],"Misconceptions about magnets","Magnet strength",{"id":1579,"section":1426,"level":1432,"prompt":1580,"check":1581,"hints":1592,"solution":1596,"skills":1597},"magnets.q008","A coil of copper wire is connected to a battery. Iron pins are placed near the coil. What is likely to happen when the current is switched on?",{"kind":1435,"options":1582,"correct":1591},[1583,1585,1587,1589],{"id":1438,"label":1584},"The coil repels all metals",{"id":1441,"label":1586},"The coil behaves like a magnet and attracts the iron pins",{"id":1444,"label":1588},"Nothing happens because copper is not magnetic",{"id":1447,"label":1590},"The battery becomes a permanent magnet",[1441],[1593,1594,1595],"Electric current in a coil can produce magnetism.","This is called an electromagnet.","Iron pins are magnetic materials, so a magnet attracts them.","When electric current flows through a coil, the coil acts like a magnet. This is an electromagnet. The coil attracts iron pins while the current is on. When the current stops, the magnetism usually disappears. Answer: The coil behaves like a magnet and attracts the iron pins.",[1598,60],"Electromagnet basics",{"id":1600,"section":1422,"level":1432,"prompt":1601,"check":1602,"hints":1613,"solution":1617,"skills":1618},"magnets.q009","A child breaks a bar magnet into two pieces. Which statement about the two pieces is true?",{"kind":1435,"options":1603,"correct":1612},[1604,1606,1608,1610],{"id":1438,"label":1605},"Each piece has one pole only: one piece is north, the other is south.",{"id":1441,"label":1607},"Each piece has both a north and a south pole.",{"id":1444,"label":1609},"Each piece has no poles because the magnet lost its magnetism.",{"id":1447,"label":1611},"Both pieces have only south poles.",[1441],[1614,1615,1616],"A bar magnet has two poles.","Breaking a magnet separates the pieces, but it does not separate the north and south poles.","Try it with a small compass: each broken piece still attracts both ends of a compass needle.","Every magnet has a north pole and a south pole. When you break a magnet, each new piece becomes a complete magnet with its own north and south pole. Poles always occur in pairs, so you cannot get an isolated north or south pole. Therefore both pieces have two poles.",[1619,1620],"magnetic poles","properties of magnets",{"id":1622,"section":1422,"level":1432,"prompt":1623,"check":1624,"hints":1635,"solution":1639,"skills":1640},"magnets.q010","A child has a bar magnet with N and S marked. She brings the N pole close to each end of an unmarked iron rod. Both ends of the rod are attracted to the N pole. What does this show?",{"kind":1435,"options":1625,"correct":1634},[1626,1628,1630,1632],{"id":1438,"label":1627},"The rod is a magnet with a south pole at both ends.",{"id":1441,"label":1629},"The rod is made of iron but is not a magnet.",{"id":1444,"label":1631},"The rod is a magnet with a north pole at both ends.",{"id":1447,"label":1633},"The rod must be made of copper.",[1441],[1636,1637,1638],"A magnet has one end that repels a north pole.","Iron is attracted to a magnet even if it is not a magnet itself.","If the rod were a magnet, the N pole of the bar magnet would repel one end.","The unmarked rod is attracted at both ends, so it behaves like ordinary iron, not like a magnet. A real magnet has two poles: the N pole of the bar magnet would attract one end and repel the other. Since both ends are attracted, the rod is made of a magnetic material, iron, but is not magnetized.",[1641,1619,1642],"magnetic vs non-magnetic","attraction",{"id":1644,"section":1422,"level":1432,"prompt":1645,"check":1646,"hints":1657,"solution":1661,"skills":1662},"magnets.q011","Which group contains only magnetic materials?",{"kind":1435,"options":1647,"correct":1656},[1648,1650,1652,1654],{"id":1438,"label":1649},"Iron, nickel, cobalt",{"id":1441,"label":1651},"Iron, copper, aluminium",{"id":1444,"label":1653},"Steel, wood, plastic",{"id":1447,"label":1655},"Nickel, brass, glass",[1438],[1658,1659,1660],"Magnetic materials are attracted by a magnet.","Copper and aluminium are metals, but they are not magnetic.","Iron, nickel and cobalt are the common magnetic metals.","Magnetic materials are attracted to magnets. The common magnetic metals are iron, nickel and cobalt. Steel contains iron, so it is also magnetic. Copper, aluminium, wood, plastic, brass and glass are not magnetic. Therefore the group with only magnetic materials is iron, nickel, cobalt.",[1663,1664],"magnetic materials","classification",{"id":1666,"section":1422,"level":1432,"prompt":1667,"check":1668,"hints":1678,"solution":1682,"skills":1683},"magnets.q012","The end of a compass needle that points towards Earth's geographic north is called what?",{"kind":1496,"accept":1669},[1670,1671,1672,1673,1674,1675,1676,1677],"north pole","north","the north pole","north-seeking pole","north magnetic pole","North Pole","north pole of the magnet","north-seeking end",[1679,1680,1681],"A compass needle is a small bar magnet.","A freely suspended magnet's north pole points north.","The opposite pole would point south.","A compass needle is a small magnet. Its north pole, also called the north-seeking pole, is the end that points towards Earth's geographic north. This happens because Earth behaves like a giant magnet.",[458,1684,1619],"Earth as magnet",{"id":1686,"section":1422,"level":1432,"prompt":1687,"check":1688,"hints":1699,"solution":1703,"skills":1704},"magnets.q013","A compass needle points north-south. Which statement best explains this?",{"kind":1435,"options":1689,"correct":1698},[1690,1692,1694,1696],{"id":1438,"label":1691},"The Sun's heat pushes the needle north.",{"id":1441,"label":1693},"Earth acts like a giant magnet.",{"id":1444,"label":1695},"The needle is attracted by strong winds.",{"id":1447,"label":1697},"Gravity pulls the needle towards the north.",[1441],[1700,1701,1702],"A compass needle is a tiny magnet.","Magnets line up with a magnetic field.","Earth has a magnetic field around it.","The compass needle is a small magnet, so it aligns with Earth's magnetic field. Earth acts like a giant magnet with magnetic poles, so the needle points north-south. It is not caused by the Sun, wind or gravity.",[458,1684,1705],"magnetic field",{"id":1707,"section":1422,"level":1432,"prompt":1708,"check":1709,"hints":1720,"solution":1724,"skills":1725},"magnets.q014","A fridge magnet sticks to a steel refrigerator door but not to a wooden cupboard door. Which statement is the best explanation?",{"kind":1435,"options":1710,"correct":1719},[1711,1713,1715,1717],{"id":1438,"label":1712},"Magnets attract all materials equally.",{"id":1441,"label":1714},"Steel is a magnetic material, but wood is not.",{"id":1444,"label":1716},"Wood repels the magnet.",{"id":1447,"label":1718},"The magnet is broken because it cannot stick to wood.",[1441],[1721,1722,1723],"A magnet attracts magnetic materials.","Wood is a non-magnetic material.","Steel contains iron, so it is magnetic.","Magnets attract magnetic materials such as iron, steel, nickel and cobalt. Steel contains iron, so the fridge door is magnetic. Wood is a non-magnetic material, so the magnet does not stick to it. Magnets do not attract all materials, and wood does not repel a magnet.",[1663,1726,1727],"everyday magnets","non-magnetic materials",{"id":1729,"section":1422,"level":1422,"prompt":1730,"check":1731,"hints":1740,"solution":1744,"skills":1745},"magnets.q015","A bar magnet is brought near four objects: an iron nail, a plastic ruler, a copper wire and an aluminium foil. Which object will stick to the magnet?",{"kind":1435,"options":1732,"correct":1739},[1733,1734,1736,1738],{"id":1438,"label":1439},{"id":1441,"label":1735},"Plastic ruler",{"id":1444,"label":1737},"Copper wire",{"id":1447,"label":1445},[1438],[1741,1742,1743],"Think about which materials are magnetic. Iron, nickel, cobalt and steel are magnetic.","Copper and aluminium are metals, but they are not attracted to a magnet.","Plastic is not a metal and is not magnetic.","The iron nail sticks because iron is a magnetic material. Copper and aluminium are metals, but they are not magnetic. Plastic is non-magnetic. So the correct answer is the iron nail.",[1746,1747,1748],"classifying magnetic materials","identifying non-magnetic metals","observing magnet attraction",{"id":1750,"section":1422,"level":1422,"prompt":1482,"check":1751,"hints":1752,"solution":1755,"skills":1756},"magnets.q016",{"kind":1484,"answer":66,"tolerance":14},[1753,1754],"Poles are the ends where a magnet's force is strongest.","A bar magnet has a north-seeking pole and a south-seeking pole.","A bar magnet has two poles: a north pole and a south pole. Even if a magnet is cut into pieces, each piece still has two poles.",[1619,1620],{"id":1758,"section":1422,"level":1422,"prompt":1460,"check":1759,"hints":1769,"solution":1773,"skills":1774},"magnets.q017",{"kind":1435,"options":1760,"correct":1768},[1761,1763,1764,1766],{"id":1438,"label":1762},"They attract each other",{"id":1441,"label":1466},{"id":1444,"label":1765},"They have no effect on each other",{"id":1447,"label":1767},"They stick only if one magnet is larger",[1441],[1770,1771,1772],"Like poles repel; unlike poles attract.","North and north are like poles.","Repulsion does not depend on the size of the magnet.","Like poles repel. Both are north poles, so they push each other away. Unlike poles, such as north and south, would attract each other.",[1619,1775,1776],"attraction and repulsion","predicting magnet behaviour",{"id":1778,"section":1422,"level":1422,"prompt":1779,"check":1780,"hints":1791,"solution":1795,"skills":1796},"magnets.q018","Which statement about magnets is TRUE?",{"kind":1435,"options":1781,"correct":1790},[1782,1784,1786,1788],{"id":1438,"label":1783},"Bigger magnets are always stronger than smaller magnets",{"id":1441,"label":1785},"Magnets attract all materials",{"id":1444,"label":1787},"A small strong magnet can be stronger than a bigger weak magnet",{"id":1447,"label":1789},"All metals are magnetic",[1444],[1792,1793,1794],"Magnet strength depends on the material and how the magnet is made, not only on size.","Magnets do not attract plastic, wood, copper or aluminium.","Only some metals, such as iron, nickel and cobalt, are magnetic.","The true statement is that a small strong magnet can be stronger than a bigger weak magnet. Strength depends on material and magnetisation, not size alone. Magnets do not attract all materials, and not all metals are magnetic.",[1797,1798,1799],"correcting misconceptions","magnet strength","scientific reasoning",{"id":1801,"section":1422,"level":1422,"prompt":1802,"check":1803,"hints":1814,"solution":1817,"skills":1818},"magnets.q019","A compass needle is a small bar magnet. In which direction does its north-seeking pole normally point?",{"kind":1435,"options":1804,"correct":1813},[1805,1807,1809,1811],{"id":1438,"label":1806},"Toward Earth's geographic north",{"id":1441,"label":1808},"Toward Earth's geographic south",{"id":1444,"label":1810},"Toward the nearest iron object",{"id":1447,"label":1812},"Toward the Sun",[1438],[1815,1527,1816],"A compass is used to find directions.","The north-seeking pole of a compass points toward geographic north.","A compass needle's north-seeking pole points toward Earth's geographic north. This happens because Earth acts like a giant magnet, with its magnetic south pole near the geographic north.",[1819,1820,1619],"compass directions","Earth's magnetism",{"id":1822,"section":1422,"level":1422,"prompt":1823,"check":1824,"hints":1835,"solution":1838,"skills":1839},"magnets.q020","A bar magnet is placed under a thin sheet of paper. Iron filings are sprinkled on top. What do the iron filings show?",{"kind":1435,"options":1825,"correct":1834},[1826,1828,1830,1832],{"id":1438,"label":1827},"A pattern of magnetic field lines around the magnet",{"id":1441,"label":1829},"The exact size of the magnet",{"id":1444,"label":1831},"A list of magnetic materials",{"id":1447,"label":1833},"An electric current in the magnet",[1438],[1836,1551,1837],"Iron filings line up along invisible magnetic field lines.","The filings do not show current or list materials.","The iron filings line up along the magnetic field lines and reveal the pattern of the magnet's magnetic field. The field is strongest near the poles.",[1705,1840,1841],"iron filings experiment","observing patterns",{"id":1843,"section":1422,"level":1422,"prompt":1844,"check":1845,"hints":1856,"solution":1860,"skills":1861},"magnets.q021","Which of these everyday objects uses a magnet?",{"kind":1435,"options":1846,"correct":1855},[1847,1849,1851,1853],{"id":1438,"label":1848},"Fridge magnet",{"id":1441,"label":1850},"Electric motor",{"id":1444,"label":1852},"Loudspeaker",{"id":1447,"label":1854},"All of these",[1447],[1857,1858,1859],"Fridge magnets stick to steel refrigerator doors.","Electric motors use magnets to spin.","Loudspeakers use magnets to make sound.","All of these use magnets. Fridge magnets stick to steel doors, electric motors use magnets to spin, and loudspeakers use magnets to make sound. Maglev trains also use strong magnets to float and move.",[1862,1863],"everyday uses of magnets","applications of magnets",{"id":1865,"section":1422,"level":1422,"prompt":1866,"check":1867,"hints":1878,"solution":1881,"skills":1882},"magnets.q022","A student says, 'All metals are magnetic.' Which pair of metals shows that this statement is wrong?",{"kind":1435,"options":1868,"correct":1877},[1869,1871,1873,1875],{"id":1438,"label":1870},"Copper and aluminium",{"id":1441,"label":1872},"Iron and steel",{"id":1444,"label":1874},"Nickel and cobalt",{"id":1447,"label":1876},"Iron and nickel",[1438],[1879,1742,1880],"Iron, nickel and cobalt are magnetic. Steel contains iron and is also magnetic.","So not all metals are magnetic.","Copper and aluminium are metals, but they are not magnetic. Therefore the statement 'all metals are magnetic' is false. Only some metals, such as iron, nickel and cobalt, and steel are magnetic.",[1797,1883,1884],"classifying materials","metals and magnetism",{"id":1886,"section":1422,"level":1422,"prompt":1887,"check":1888,"hints":1899,"solution":1902,"skills":1903},"magnets.q023","Which list contains only magnetic materials?",{"kind":1435,"options":1889,"correct":1898},[1890,1892,1894,1896],{"id":1438,"label":1891},"iron, nickel, cobalt",{"id":1441,"label":1893},"iron, copper, aluminium",{"id":1444,"label":1895},"wood, plastic, glass",{"id":1447,"label":1897},"steel, brass, aluminium",[1438],[1900,1452,1901],"A magnetic material is pulled strongly by a magnet.","Steel is magnetic, but brass and aluminium are not.","Magnetic materials are materials that a magnet attracts. Iron, nickel and cobalt are magnetic materials. Steel is also magnetic because it contains iron. Copper, aluminium, wood, plastic, glass and brass are not magnetic. So the only list with only magnetic materials is iron, nickel, cobalt.",[1904,1905,1906],"identify magnetic materials","classify metals","recall iron nickel cobalt",{"id":1908,"section":1422,"level":1422,"prompt":1909,"check":1910,"hints":1911,"solution":1915,"skills":1916},"magnets.q024","A bar magnet is broken into two pieces. How many magnetic poles are there in total on the two pieces?",{"kind":1484,"answer":90,"tolerance":14},[1912,1913,1914],"Every bar magnet has a north pole and a south pole.","When you break a magnet, each piece becomes a complete magnet.","Count the poles on each piece.","A magnet always has two poles: a north pole and a south pole. Breaking a bar magnet does not separate the poles. Each broken piece becomes a smaller magnet with its own north and south pole. So two pieces have 2 + 2 = 4 magnetic poles in total.",[1917,1918,1919],"poles of a magnet","magnet breaking","magnetic poles exist in pairs",{"id":1921,"section":1422,"level":1422,"prompt":1922,"check":1923,"hints":1934,"solution":1938,"skills":1939},"magnets.q025","A bar magnet is dipped into a pile of iron filings and then lifted out. Where do most iron filings stick on the magnet?",{"kind":1435,"options":1924,"correct":1933},[1925,1927,1929,1931],{"id":1438,"label":1926},"Evenly along the whole length",{"id":1441,"label":1928},"Only at the middle",{"id":1444,"label":1930},"Near both ends\u002Fpoles",{"id":1447,"label":1932},"Only at the north pole",[1444],[1935,1936,1937],"The ends of a bar magnet are called poles.","The magnetic force is strongest at the poles.","A bar magnet has two poles, not one.","The magnetic force of a bar magnet is strongest at its two poles: the north and south ends. The middle of a bar magnet is weak. So when iron filings are attracted, most of them stick near both ends, not evenly and not only at one pole.",[1619,1940,1840],"strength of magnetic force",{"id":1942,"section":1422,"level":1422,"prompt":1943,"check":1944,"hints":1955,"solution":1959,"skills":1960},"magnets.q026","The south pole of one bar magnet is brought close to the north pole of another bar magnet. What will happen?",{"kind":1435,"options":1945,"correct":1954},[1946,1948,1950,1952],{"id":1438,"label":1947},"They will repel each other.",{"id":1441,"label":1949},"They will attract each other.",{"id":1444,"label":1951},"They will not affect each other.",{"id":1447,"label":1953},"They will become hot.",[1441],[1956,1957,1958],"Like poles repel.","Unlike poles attract.","South and north are unlike poles.","Magnets have two types of poles: north and south. Like poles, such as north-north or south-south, push each other away, or repel. Unlike poles, such as north-south, pull towards each other, or attract. A south pole and a north pole are unlike poles, so they attract.",[1775,1619,1961],"like and unlike poles",{"id":1963,"section":1422,"level":1422,"prompt":1964,"check":1965,"hints":1976,"solution":1980,"skills":1981},"magnets.q027","A bar magnet is placed under a thin sheet of paper, and an iron nail is placed on top of the paper. The nail still moves when the magnet is moved. What does this show?",{"kind":1435,"options":1966,"correct":1975},[1967,1969,1971,1973],{"id":1438,"label":1968},"Magnetic force can act through paper.",{"id":1441,"label":1970},"Paper is a magnetic material.",{"id":1444,"label":1972},"The magnet attracts all materials.",{"id":1447,"label":1974},"Paper blocks all magnetic force.",[1438],[1977,1978,1979],"The nail is not touching the magnet.","Paper is non-magnetic.","If the nail moves, the magnetic force has reached it through the paper.","The iron nail is separated from the magnet by the paper, but it still moves. This shows that magnetic force can pass through non-magnetic materials such as paper, plastic or glass. It does not mean paper is magnetic, and magnets do not attract all materials.",[1982,1727,1983],"magnetic force","magnetic field action through materials",{"id":1985,"section":1422,"level":1422,"prompt":1986,"check":1987,"hints":1998,"solution":2002,"skills":2003},"magnets.q028","A student says, 'A bigger magnet is always stronger than a smaller magnet.' Which statement is correct?",{"kind":1435,"options":1988,"correct":1997},[1989,1991,1993,1995],{"id":1438,"label":1990},"The student is right: size is the only thing that decides strength.",{"id":1441,"label":1992},"The student is wrong: strength depends on the material and how it is magnetised.",{"id":1444,"label":1994},"The student is wrong: smaller magnets are always stronger.",{"id":1447,"label":1996},"The student is right: all magnets of the same size are equally strong.",[1441],[1999,2000,2001],"A small strong magnet can be stronger than a larger weak magnet.","A magnet's strength is not decided only by its size.","Think about what the magnet is made from.","Size is not the only factor that decides a magnet's strength. The magnetic material and the way it is magnetised matter a lot. A small strong magnet can be stronger than a bigger weak magnet. So the statement 'bigger is always stronger' is a misconception.",[1798,2004,1663],"misconception about size",{"id":2006,"section":1422,"level":1422,"prompt":2007,"check":2008,"hints":2019,"solution":2023,"skills":2024},"magnets.q029","A fridge magnet sticks to the steel door of a refrigerator. Why does it stick?",{"kind":1435,"options":2009,"correct":2018},[2010,2012,2014,2016],{"id":1438,"label":2011},"Steel contains iron, so it is attracted to a magnet.",{"id":1441,"label":2013},"The refrigerator door is made of plastic.",{"id":1444,"label":2015},"Magnets stick to all metals.",{"id":1447,"label":2017},"The fridge door is made of copper.",[1438],[2020,2021,2022],"Steel contains iron.","Iron is a magnetic material.","Magnets do not attract all metals.","The refrigerator door is made of steel. Steel contains iron, which is a magnetic material. A fridge magnet is attracted to the iron in the steel. Magnets do not stick to all metals: copper and aluminium, for example, are not magnetic.",[1862,1663,2025],"steel contains iron",{"id":2027,"section":1422,"level":1422,"prompt":2028,"check":2029,"hints":2040,"solution":2044,"skills":2045},"magnets.q030","What is a magnetic field?",{"kind":1435,"options":2030,"correct":2039},[2031,2033,2035,2037],{"id":1438,"label":2032},"The region around a magnet where its magnetic force can act",{"id":1441,"label":2034},"The shiny surface of a magnet",{"id":1444,"label":2036},"The line drawn exactly at the middle of a magnet",{"id":1447,"label":2038},"A type of electric current",[1438],[2041,2042,2043],"A magnet can attract an iron nail without touching it.","The force is strongest near the poles.","Iron filings around a magnet arrange along the field.","A magnetic field is the space around a magnet where magnetic force can be felt by magnetic materials such as iron. Iron filings sprinkled around a bar magnet line up along the magnetic field. It is not just the surface, a middle line, or an electric current.",[1705,1982,2046],"iron filings pattern",{"id":2048,"section":1422,"level":1422,"prompt":2049,"check":2050,"hints":2059,"solution":2062,"skills":2063},"magnets.q031","A learner places a bar magnet close to each of these objects: an iron nail, a copper coin, an aluminium foil ball, and a plastic button. Which object is attracted to the magnet?",{"kind":1435,"options":2051,"correct":2058},[2052,2053,2054,2056],{"id":1438,"label":1439},{"id":1441,"label":1442},{"id":1444,"label":2055},"Aluminium foil ball",{"id":1447,"label":2057},"Plastic button",[1438],[2060,2061,1743],"A magnet attracts materials that are magnetic, not every material.","Iron is a common magnetic material; copper and aluminium are metals but not magnetic.","A bar magnet attracts magnetic materials. Iron is magnetic, so the iron nail is attracted. Copper and aluminium are metals, but they are not magnetic. Plastic is not magnetic either. Therefore the correct object is the iron nail.",[1663,1727,1664],{"id":2065,"section":1422,"level":1422,"prompt":2066,"check":2067,"hints":2078,"solution":2081,"skills":2082},"magnets.q032","The north pole of one bar magnet is brought near the north pole of another bar magnet. What will happen?",{"kind":1435,"options":2068,"correct":2077},[2069,2071,2073,2075],{"id":1438,"label":2070},"They will attract each other",{"id":1441,"label":2072},"They will repel each other",{"id":1444,"label":2074},"Nothing will happen",{"id":1447,"label":2076},"They will attract only if one magnet is larger",[1441],[2079,2080,1475],"Every magnet has a north pole and a south pole.","Like poles behave in the same way: north-north and south-south.","Two north poles are like poles. Like magnetic poles repel each other, so the two north poles will push apart. Unlike poles, such as north and south, attract each other. Therefore the correct answer is that they will repel each other.",[1619,2083,2084],"repulsion","like poles",{"id":2086,"section":1426,"level":1426,"prompt":2087,"check":2088,"hints":2099,"solution":2102,"skills":2103},"magnets.q033","A student has a shiny one-rupee coin, an iron nail, aluminium foil, a copper wire, a steel paper clip, a wooden pencil and a plastic ruler. She tests each one with a bar magnet. Which list contains **only** objects that will be attracted to the magnet?",{"kind":1435,"options":2089,"correct":2098},[2090,2092,2094,2096],{"id":1438,"label":2091},"Iron nail and steel paper clip",{"id":1441,"label":2093},"Iron nail, copper wire and steel paper clip",{"id":1444,"label":2095},"Shiny one-rupee coin, iron nail and aluminium foil",{"id":1447,"label":2097},"Aluminium foil, copper wire and steel paper clip",[1438],[2100,2101,1659],"Only materials that are magnetic, such as iron and steel, are pulled by a magnet.","A shiny coin may look like iron but Indian rupee coins are often made of non-magnetic metals.","A bar magnet attracts magnetic materials. The common magnetic elements are iron, nickel and cobalt; steel contains iron, so steel is also attracted. Copper, aluminium, wood, plastic and most coins are not magnetic. In the list, only the iron nail and steel paper clip are magnetic. So the correct list is a.",[1746,2104,2105],"identifying misconceptions","experimental testing",{"id":2107,"section":1426,"level":1426,"prompt":2108,"check":2109,"hints":2120,"solution":2124,"skills":2125},"magnets.q034","Two unmarked bar magnets are brought close together. End X of magnet 1 and end Y of magnet 2 push each other apart strongly. What does this tell you about ends X and Y?",{"kind":1435,"options":2110,"correct":2119},[2111,2113,2115,2117],{"id":1438,"label":2112},"They are like poles (both north or both south).",{"id":1441,"label":2114},"They are unlike poles (one north and one south).",{"id":1444,"label":2116},"One end is magnetic and the other is not magnetic.",{"id":1447,"label":2118},"The magnets have lost their poles.",[1438],[2121,2122,2123],"Remember: like poles repel, unlike poles attract.","If two ends push apart, they must be the same kind of pole.","A north pole repels another north pole; a south pole repels another south pole.","Magnets have two poles: north and south. When two like poles come near each other, they repel; when unlike poles come near each other, they attract. Since the ends push apart, ends X and Y must be like poles. Correct answer: a.",[2126,2083,2127],"poles","interpreting observations",{"id":2129,"section":1426,"level":1426,"prompt":2130,"check":2131,"hints":2142,"solution":2146,"skills":2147},"magnets.q035","A bar magnet is placed flat under a sheet of thin card. Iron filings are sprinkled on top of the card and gently tapped. The filings arrange themselves in curved lines from one pole to the other. Which statement best explains this pattern?",{"kind":1435,"options":2132,"correct":2141},[2133,2135,2137,2139],{"id":1438,"label":2134},"The iron filings become tiny temporary magnets and line up along the magnetic field.",{"id":1441,"label":2136},"The filings stick to the card because the card is magnetic.",{"id":1444,"label":2138},"The filings are pushed only to the exact middle of the magnet.",{"id":1447,"label":2140},"The pattern is random and has nothing to do with the magnet.",[1438],[2143,2144,2145],"Each iron filing behaves like a tiny compass needle when it is near a magnet.","The magnet creates an invisible magnetic field around itself.","The filings show the shape of the field lines, not the card.","A magnet creates a magnetic field in the space around it. Iron filings are made of iron, so each small filing becomes an induced magnet and aligns with the magnetic field. The curved lines show the field lines running from the north pole to the south pole outside the magnet. Correct answer: a.",[1705,2148,2149],"iron filings","field lines",{"id":2151,"section":1426,"level":1426,"prompt":2152,"check":2153,"hints":2164,"solution":2168,"skills":2169},"magnets.q036","A compass needle is a small bar magnet that is free to turn. Its N-pole points roughly towards Earth's geographic North Pole. What does this tell us about Earth's magnetic pole near the geographic North Pole?",{"kind":1435,"options":2154,"correct":2163},[2155,2157,2159,2161],{"id":1438,"label":2156},"There is a magnetic south pole near Earth's geographic North Pole.",{"id":1441,"label":2158},"There is a magnetic north pole near Earth's geographic North Pole.",{"id":1444,"label":2160},"Earth has no magnetic field near the North Pole.",{"id":1447,"label":2162},"The compass needle is not affected by Earth.",[1438],[2165,2166,2167],"Opposite magnetic poles attract.","The N-pole of a compass points north because it is attracted to a magnetic south pole.","Earth behaves like a giant bar magnet hidden inside the planet.","A compass N-pole is attracted to a magnetic south pole. Since the compass N-pole points towards Earth's geographic North Pole, Earth must have a magnetic south pole near the geographic North Pole. That is why the north-seeking end of the needle points north. Correct answer: a.",[1820,458,1619],{"id":2171,"section":1426,"level":1426,"prompt":2172,"check":2173,"hints":2184,"solution":2188,"skills":2189},"magnets.q037","A group makes an electromagnet by winding 20 turns of insulated copper wire around an iron nail and connecting the wire to a single 1.5 V cell. It picks up 8 paper clips. Which single change is most likely to make the electromagnet pick up more paper clips?",{"kind":1435,"options":2174,"correct":2183},[2175,2177,2179,2181],{"id":1438,"label":2176},"Increase the number of turns of wire around the iron nail.",{"id":1441,"label":2178},"Replace the iron nail with a wooden dowel of the same size.",{"id":1444,"label":2180},"Reduce the number of turns of wire around the iron nail.",{"id":1447,"label":2182},"Disconnect one end of the wire from the cell.",[1438],[2185,2186,2187],"An electromagnet becomes stronger when more electric current flows through more turns.","The iron core helps concentrate the magnetic field; a wooden core does not.","Disconnecting the wire stops the current, so the electromagnet stops working.","An electromagnet is a coil of current-carrying wire, often around an iron core. Its strength increases if you increase the number of turns of the coil or increase the current. Replacing the iron core with wood weakens it, reducing turns weakens it, and disconnecting the wire stops the current. So the best change is a.",[2190,2191,2192],"electromagnet","electric current","coil turns",{"id":2194,"section":1426,"level":1426,"prompt":2195,"check":2196,"hints":2198,"solution":2202,"skills":2203},"magnets.q038","In a fair test, an electromagnet with 20 turns of wire picks up 12 steel paper clips. Every extra 10 turns adds exactly 3 more paper clips. How many paper clips would you predict the electromagnet will pick up with 50 turns?",{"kind":1484,"answer":237,"tolerance":14,"unit":2197},"paper clips",[2199,2200,2201],"Find how many extra turns are added: 50 − 20.","Divide the extra turns by 10 to find how many 3-clip increases happen.","Start with 12 clips and add the extra clips.","From 20 turns to 50 turns the extra turns are 50 − 20 = 30 turns. Every 10 extra turns adds 3 paper clips, so 30 extra turns adds 3 × 3 = 9 paper clips. Starting from 12 clips, predicted clips = 12 + 9 = 21 paper clips.",[2204,2205,2206],"electromagnet strength","prediction","fair test",{"id":2208,"section":1426,"level":1426,"prompt":2209,"check":2210,"hints":2218,"solution":2222,"skills":2223},"magnets.q039","Name one magnetic element, other than iron, that a bar magnet will attract. Give the element name only.",{"kind":1496,"accept":2211},[2212,2213,2214,2215,2216,2217],"nickel","cobalt","nickel (Ni)","cobalt (Co)","Ni","Co",[2219,2220,2221],"The three common magnetic elements are iron, nickel and cobalt.","Steel is magnetic because it contains iron, but it is not an element.","Aluminium and copper are metals, but they are not magnetic elements.","The magnetic elements are iron, nickel and cobalt. Since the question asks for one other than iron, accepted answers are nickel or cobalt.",[2224,2225],"magnetic elements","recall",{"id":2227,"section":1426,"level":1426,"prompt":2228,"check":2229,"hints":2240,"solution":2244,"skills":2245},"magnets.q040","A child says: 'A bigger magnet is always stronger.' Which observation best shows that this statement is **not always true**?",{"kind":1435,"options":2230,"correct":2239},[2231,2233,2235,2237],{"id":1438,"label":2232},"A small but powerful neodymium magnet can lift more steel paper clips than a large ordinary iron magnet.",{"id":1441,"label":2234},"A large magnet is heavier than a small magnet.",{"id":1444,"label":2236},"A small magnet can be painted red.",{"id":1447,"label":2238},"A large magnet has two poles.",[1438],[2241,2242,2243],"Strength depends on the material and how the magnet is made, not only on size.","Neodymium magnets can be very strong even when they are small.","Weight or colour does not tell you magnetic strength.","Size is not the only factor in magnetic strength. The material and the way a magnet is made matter too. A small neodymium magnet can be much stronger than a larger ordinary iron magnet. So the observation in a best shows the statement is not always true.",[1798,2246,2127],"misconceptions",{"id":2248,"section":1426,"level":1426,"prompt":2249,"check":2250,"hints":2261,"solution":2265,"skills":2266},"magnets.q041","Four rods look identical: one is made of copper, one of aluminium, one of soft iron and one of steel. A student strokes each rod with one pole of a strong bar magnet, always in the same direction, then dips each rod into a pile of iron filings. The copper and aluminium rods pick up almost no filings. The iron and steel rods each pick up some filings. Which conclusion is best supported?",{"kind":1435,"options":2251,"correct":2260},[2252,2254,2256,2258],{"id":1438,"label":2253},"Copper and aluminium are magnetic elements.",{"id":1441,"label":2255},"Iron and steel can be magnetised, but copper and aluminium cannot be magnetised easily.",{"id":1444,"label":2257},"All metals can be magnetised if stroked long enough.",{"id":1447,"label":2259},"Only steel is attracted to a magnet.",[1441],[2262,2263,2264],"Think about which materials are magnetic elements or can behave like magnets.","Stroking with a magnet can line up tiny magnetic regions in some metals.","Copper and aluminium are metals, but they do not become magnets.","Iron and steel are magnetic materials: steel is mostly iron, so both can be magnetised by stroking with a magnet. Copper and aluminium are metals, but they are not magnetic materials and do not become magnets when stroked. So the best conclusion is that iron and steel can be magnetised, but copper and aluminium cannot be magnetised easily. This also shows that not all metals are magnetic.",[1511,2267,2268,2269],"Magnetising by stroking","Fair testing","Misconception: all metals are magnetic",{"id":2271,"section":1426,"level":1426,"prompt":2272,"check":2273,"hints":2284,"solution":2288,"skills":2289},"magnets.q042","A bar magnet is broken into two equal pieces. A student says: 'One piece will be a north pole and the other piece will be a south pole.' Which statement is correct?",{"kind":1435,"options":2274,"correct":2283},[2275,2277,2279,2281],{"id":1438,"label":2276},"The student is correct because poles can be separated.",{"id":1441,"label":2278},"The student is wrong; each piece will have both a north and a south pole.",{"id":1444,"label":2280},"The student is wrong; both pieces will be only north poles.",{"id":1447,"label":2282},"The student is wrong; both pieces will lose all magnetism.",[1441],[2285,2286,2287],"A single magnetic pole has never been found.","Try breaking a magnet into tiny pieces in your mind: what happens to each piece?","Each piece becomes a complete smaller magnet.","Magnetic poles always occur in pairs. When a bar magnet is cut, each piece becomes a smaller magnet with its own north pole and south pole. So the student is wrong: each piece has both a north and a south pole.",[2290,2291,2292],"Magnetic poles","Poles always occur in pairs","Magnet behaviour",{"id":2294,"section":1426,"level":1426,"prompt":2295,"check":2296,"hints":2307,"solution":2311,"skills":2312},"magnets.q043","Earth behaves like a huge bar magnet. A compass needle's north-seeking end points roughly towards Earth's geographic North. Which statement about Earth's magnetic poles is correct?",{"kind":1435,"options":2297,"correct":2306},[2298,2300,2302,2304],{"id":1438,"label":2299},"Earth's magnetic south pole is near the geographic North.",{"id":1441,"label":2301},"Earth's magnetic north pole is near the geographic North.",{"id":1444,"label":2303},"Earth's magnetic poles lie on the equator.",{"id":1447,"label":2305},"Earth does not have magnetic poles; only the compass has poles.",[1438],[2308,2309,2310],"Opposite magnetic poles attract each other.","A compass N-pole points north because it is attracted by a magnetic pole near there.","What kind of pole must be near geographic North to attract a compass N-pole?","A compass needle's north-seeking pole is attracted to an opposite magnetic pole, which is a magnetic south pole. Since the compass N-pole points towards Earth's geographic North, Earth's magnetic south pole must be near the geographic North. So the correct statement is option a.",[1820,2313,2290,2314],"Compass","Opposite poles attract",{"id":2316,"section":1426,"level":1426,"prompt":2317,"check":2318,"hints":2329,"solution":2332,"skills":2333},"magnets.q044","A student magnetises a sewing needle by stroking it with one pole of a bar magnet, always in the same direction. She floats the needle on a small piece of paper in water. It swings to point north-south. She wants to know which end of the needle is its north pole. Which test is correct?",{"kind":1435,"options":2319,"correct":2328},[2320,2322,2324,2326],{"id":1438,"label":2321},"Bring the known north pole of a bar magnet close to one end. If that end is repelled, it is a north pole.",{"id":1441,"label":2323},"Bring the known north pole close to one end. If that end is attracted, it is a north pole.",{"id":1444,"label":2325},"Bring the known south pole close to one end. If that end is repelled, it is a north pole.",{"id":1447,"label":2327},"Drop the needle and see which end hits the floor first.",[1438],[1770,2330,2331],"A known north pole will repel another north pole.","Use the known pole and watch for repulsion, not attraction, to identify the same pole.","Bring the marked north pole of a bar magnet close to one end of the needle. If that end is pushed away, it is also a north pole because like poles repel. If it is attracted, that end is a south pole. So option a is the correct test.",[2334,2335,2336],"Like poles repel","Identifying magnetic poles","Investigating magnets",{"id":2338,"section":1422,"level":2339,"prompt":2340,"check":2341,"hints":2352,"solution":2356,"skills":2357},"magnets.q045","challenge","A learner has five objects: an iron nail, a nickel coin, a cobalt piece, a copper wire and an aluminium foil. She tests each object by bringing a strong bar magnet close to it. Which objects will be attracted to the magnet?",{"kind":1435,"options":2342,"correct":2351},[2343,2345,2347,2349],{"id":1438,"label":2344},"Iron nail, nickel coin and cobalt piece",{"id":1441,"label":2346},"Iron nail, copper wire and aluminium foil",{"id":1444,"label":2348},"All five objects, because they are all metals",{"id":1447,"label":2350},"Only the iron nail, because only iron is magnetic",[1438],[2353,2354,2355],"Think about which metals are magnetic materials.","Copper and aluminium are metals, but are they magnetic?","Nickel and cobalt are magnetic, just like iron.","Magnetic materials are attracted to magnets. The common magnetic metals are iron, nickel and cobalt (and steel, because it contains iron). Copper and aluminium are metals, but they are not magnetic. So the iron nail, nickel coin and cobalt piece are attracted, while the copper wire and aluminium foil are not. This also corrects the misconception that all metals are magnetic.",[2358,2359,2360],"identifying magnetic materials","classifying metals","misconception: all metals magnetic",{"id":2362,"section":1422,"level":2339,"prompt":2363,"check":2364,"hints":2365,"solution":2369,"skills":2370},"magnets.q046","A bar magnet is broken into four smaller pieces. How many north poles are there in total among all four pieces?",{"kind":1484,"answer":90,"tolerance":14},[2366,2367,2368],"What happens to a magnet when it is broken?","Does each piece keep both a north pole and a south pole?","Count the north poles on all pieces.","When a bar magnet is broken, every piece becomes a complete magnet with its own north pole and south pole. If there are four pieces, there are four north poles in total (and four south poles). So the answer is 4.",[1917,1918,2371],"magnetic domains",{"id":2373,"section":1422,"level":2339,"prompt":2374,"check":2375,"hints":2386,"solution":2389,"skills":2390},"magnets.q047","A compass needle has a north-seeking end that points towards Earth's geographic north. What is actually present near Earth's geographic north that makes the compass needle point that way?",{"kind":1435,"options":2376,"correct":2385},[2377,2379,2381,2383],{"id":1438,"label":2378},"A magnetic south pole",{"id":1441,"label":2380},"A magnetic north pole",{"id":1444,"label":2382},"No magnetic pole at all",{"id":1447,"label":2384},"A large piece of iron",[1438],[2165,2387,2388],"A compass north-seeking end is a north pole.","To attract a north pole, Earth's geographic north must have which magnetic pole?","The north-seeking end of a compass needle is itself a magnetic north pole. Opposite poles attract, so it must be attracted to a magnetic south pole. Earth behaves like a giant bar magnet, and its magnetic south pole is near the geographic north. That is why the compass north end points to geographic north.",[1820,458,1619],{"id":2392,"section":1422,"level":2339,"prompt":2393,"check":2394,"hints":2405,"solution":2409,"skills":2410},"magnets.q048","A learner places a sheet of paper over a bar magnet and sprinkles iron filings on the paper. The filings form curved lines between the magnet's poles. Why do the iron filings arrange themselves in this pattern?",{"kind":1435,"options":2395,"correct":2404},[2396,2398,2400,2402],{"id":1438,"label":2397},"Each filing becomes a small temporary magnet and aligns with the magnetic field",{"id":1441,"label":2399},"The filings are glued to the paper by the magnet's heat",{"id":1444,"label":2401},"Air currents push the filings into curves",{"id":1447,"label":2403},"The filings are repelled by the middle of the magnet",[1438],[2406,2407,2408],"What happens to a piece of iron when it is near a magnet?","The pattern shows the direction of the magnetic field.","Think of each filing as a tiny compass needle.","Iron filings are tiny pieces of iron. When placed in a magnetic field, each filing becomes an induced magnet (a temporary magnet). Each filing then lines up along the direction of the magnetic field, just like a tiny compass needle. The curved pattern shows the magnetic field lines around the bar magnet.",[1705,2148,2411],"induced magnetism",{"id":2413,"section":1426,"level":2339,"prompt":2414,"check":2415,"hints":2419,"solution":2423,"skills":2424},"magnets.q049","A small bar magnet can just hold a chain of 5 identical steel paper clips hanging from it. Each paper clip has a mass of 2 g. What is the minimum upward magnetic force, in newtons, needed to hold the whole chain? Use g = 10 N\u002Fkg.",{"kind":1484,"answer":2416,"tolerance":2417,"unit":2418},0.1,0.005,"N",[2420,2421,2422],"First find the total mass of the chain.","Convert the mass from grams to kilograms.","Use weight = mass × g, and remember the magnetic force must balance the weight.","Total mass of 5 paper clips = 5 × 2 g = 10 g. Convert to kilograms: 10 g = 0.010 kg. The weight of the chain is mass × g = 0.010 kg × 10 N\u002Fkg = 0.1 N. The magnet must pull upward with at least 0.1 N to hold the chain, so the minimum upward magnetic force is 0.1 N.",[2425,549,1982],"force calculation",{"id":2427,"section":1426,"level":2339,"prompt":2428,"check":2429,"hints":2440,"solution":2444,"skills":2445},"magnets.q050","A learner makes an electromagnet by coiling insulated copper wire around an iron nail and connecting it to a single cell. It picks up 3 paper clips. Which change is most likely to make the electromagnet pick up more paper clips?",{"kind":1435,"options":2430,"correct":2439},[2431,2433,2435,2437],{"id":1438,"label":2432},"Use fewer turns of wire and replace the iron nail with a plastic core",{"id":1441,"label":2434},"Use more turns of wire and add another cell in series",{"id":1444,"label":2436},"Replace the iron nail with an aluminium nail and use a shorter wire",{"id":1447,"label":2438},"Keep the same coil but move the cell farther away from the nail",[1441],[2441,2442,2443],"What makes an electromagnet stronger?","More current or more coils increases the magnetic effect.","An iron core helps because iron is magnetic.","An electromagnet gets stronger if you increase the number of turns in the coil or increase the current through the wire. Adding another cell in series increases the current, and more turns add more magnetic effect. The iron core is also important because iron is magnetic. So the best change is to use more turns of wire and add another cell in series.",[2446,2447,2448],"electromagnets","current and magnetism","coils",{"id":2450,"section":1426,"level":2339,"prompt":2451,"check":2452,"hints":2463,"solution":2467,"skills":2468},"magnets.q051","In a maglev train, electromagnets on the train and magnets on the track are arranged so that their north poles face each other. What effect does this arrangement have, and why?",{"kind":1435,"options":2453,"correct":2462},[2454,2456,2458,2460],{"id":1438,"label":2455},"It lifts the train upward because like poles repel",{"id":1441,"label":2457},"It pulls the train downward because unlike poles attract",{"id":1444,"label":2459},"It has no effect because both poles are north",{"id":1447,"label":2461},"It stops all magnetic forces because the train is heavy",[1438],[2464,2465,2466],"What happens when two north poles are brought near each other?","Like magnetic poles repel each other.","The repulsion can push against gravity.","When two north poles face each other, they repel because like magnetic poles repel. In a maglev train, this repulsion between the train's electromagnets and the track magnets produces an upward force that can lift the train, reducing contact and friction with the track.",[2469,2470,1863],"magnetic repulsion","maglev",{"id":2472,"section":1426,"level":2339,"prompt":2473,"check":2474,"hints":2485,"solution":2489,"skills":2490},"magnets.q052","A large aluminium block and a small iron nail are placed near a strong magnet. Which one is attracted to the magnet, and why?",{"kind":1435,"options":2475,"correct":2484},[2476,2478,2480,2482],{"id":1438,"label":2477},"Both are attracted, because both are metals",{"id":1441,"label":2479},"Only the iron nail, because iron is magnetic and aluminium is not",{"id":1444,"label":2481},"Only the aluminium block, because it is bigger",{"id":1447,"label":2483},"Neither, because the magnet is too strong",[1441],[2486,2487,2488],"Is aluminium a magnetic material?","Size does not decide whether a magnet attracts something.","Magnetic attraction depends on the material.","The magnet attracts the iron nail but not the aluminium block. Iron is a magnetic material, so a magnet pulls on it. Aluminium is a metal but is not magnetic. The size of the object does not matter here: a big aluminium block is still non-magnetic, and a small iron nail is still magnetic. This corrects the misconception that all metals are magnetic and that bigger objects are always attracted more strongly.",[1663,2491,2492],"non-magnetic metals","misconception: size",[2494,2495,2496],"magnets-ncert-curiosity-6-ch4","elec-deepen-eia-generation","tides-nasa-moon-tides","needs_review",{"generatedBy":2499,"notes":2500},"claude-code","generated from work item wi-9af92250","339e4ea7f6c02ae3b2069f97aafb3c760893aa0e3363b95747ec9ba2925dd363",{},"generation-94d24324-6289-4ca6-a1ff-60800dc27048"]