[{"data":1,"prerenderedAt":1046},["ShallowReactive",2],{"layer:electricity:discover":3},{"layer":4,"contentHash":1025,"dependencyHashes":1026,"approval":1040,"releaseId":1045},{"schemaVersion":5,"conceptId":6,"locale":7,"depth":8,"revision":5,"title":9,"subtitle":10,"summary":11,"objectives":12,"estimatedMinutes":18,"plate":19,"blocks":40,"sourceIds":1020,"reviewStatus":1021,"authoring":1022},1,"electricity","en","discover","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.",[13,14,15,16,17],"Describe electricity as moving charge, using atoms, protons and free electrons.","Tell static electricity from current electricity using everyday examples, including lightning.","Explain why a bulb lights instantly even though electrons drift slower than a snail.","Sort materials into conductors, insulators and semiconductors, and explain why a circuit needs a complete loop.","Name DC and AC, describe how a day depends on electricity, and state the first safety rules.",35,{"title":20,"rows":21},"Discover",[22,25,28,31,34,37],{"label":23,"value":24},"Depth","Discover (first look)",{"label":26,"value":27},"Reading time","About 35 minutes",{"label":29,"value":30},"Prior knowledge","None; simple multiplication and division",{"label":32,"value":33},"Chapters","11",{"label":35,"value":36},"Labs","2 circuit labs, 2 try-at-home activities",{"label":38,"value":39},"Units used","V, Hz, C, mm\u002Fs (names only)",[41,45,48,54,60,81,84,90,95,100,108,137,140,145,148,168,173,178,196,202,205,209,248,263,268,273,278,284,331,336,341,345,350,357,385,389,406,421,434,438,443,446,451,475,514,523,539,543,546,551,554,615,620,624,629,632,660,664,678,683,686,722,778,781,785,790,793,826,830,843,847,852,987,990,1008],{"id":42,"type":43,"markdown":44},"intro-switch","prose","Press a switch and the room lights up. Tap a phone and a payment reaches a shop across the city. Turn a knob and the mixie roars. We do this dozens of times a day without a second thought, yet every one of those moments depends on something nobody has ever seen: tiny particles, far smaller than atoms, being nudged along wires.\n\nThis layer is your first proper look at that invisible traffic. By the end you will be able to say, in plain words, what electricity *is*, why a spark from a doorknob and the power in a ceiling fan are cousins, why the light comes on instantly even though the particles inside the wire crawl slower than a snail, and why a single break in a wire can darken a whole string of festival lights.",{"id":46,"type":43,"markdown":47},"intro-promise","The big idea fits in five words: **electricity is charge on the move.** Everything else in this layer, from lightning to your phone charger to the rules about kite strings, is that one idea seen from a different angle.\n\nYou do not need any maths beyond simple multiplication and division. The formal tools (voltage, current and resistance, measured and calculated) come in the next layer, *Understand*. Here we build the picture those tools will later describe.",{"id":49,"type":50,"title":51,"eyebrow":52,"navLabel":53},"ch-atoms","chapter","Everything is already full of electricity","Chapter 01","1 Atoms and charge",{"id":55,"type":43,"markdown":56,"help":57},"atoms-inside","Pick up anything near you: a steel spoon, a notebook, a glass of water. It is made of **atoms**, so small that a single grain of salt contains more than a billion billion of them. Every atom has two parts that matter for this story:\n\n- a tiny, heavy centre called the **nucleus**, which contains **protons** (plus neutral particles called neutrons), and\n- a cloud of much lighter **electrons** around it.\n\nProtons and electrons carry something called **electric charge**. A proton's charge is called *positive* (+) and an electron's is called *negative* (−). The names are just labels chosen long ago; nothing is \"missing\" from a negative charge. What matters is how charges behave: **opposite charges pull on each other, and like charges push each other away.**\n\nAn ordinary atom has exactly as many electrons as protons, so the pluses and minuses balance and the atom as a whole is **neutral**. That is why your spoon does not stick to your hand or spark when you touch it. It is packed with charge, but perfectly balanced charge.",{"simplerExplanation":58,"anotherExample":59},"Everything is made of atoms. Atoms contain positive bits (protons) and negative bits (electrons). Normally there are equal numbers, so they cancel out and nothing seems to happen.","Think of a cricket team's scoreboard where every run scored is cancelled by a penalty run. There is a lot going on, but the total stays at zero. An atom is like that: lots of charge, net total zero.",{"id":61,"type":62,"tone":63,"items":64},"atom-spec","spec","blue",[65,69,73,77],{"label":66,"big":67,"value":68},"Proton","+1","Sits in the nucleus. Heavy: about 1,836 times the mass of an electron. Does not move through a wire.",{"label":70,"big":71,"value":72},"Electron","−1","Light and, in metals, some are free to wander. **These are the particles that move in a wire.**",{"label":74,"big":75,"value":76},"Neutron","0","Also in the nucleus. No charge, so it plays no part in ordinary electricity.",{"label":78,"big":79,"value":80},"Charge unit","1 C","One **coulomb** is the charge of about 6.24 × 10¹⁸ electrons: six billion billion.",{"id":82,"type":43,"markdown":83},"free-electrons","Here is the key difference between materials. In most substances, every electron is held firmly by its own atom. But in **metals** such as copper and aluminium, each atom lets go of one or two of its outer electrons. These **free electrons** are not tied to any particular atom; they wander through the metal like a gas trapped inside the solid.\n\nA copper wire is therefore not an empty pipe waiting for electricity to arrive. It is **already full** of free electrons, about 8.5 × 10²² of them in every cubic centimetre (that is 85,000 billion billion). Electricity in a wire does not mean pouring electrons in from outside. It means giving the electrons that are already there a steady nudge in one direction.",{"id":85,"type":86,"variant":87,"title":88,"markdown":89},"crowd-hall","callout","example","The crowd in a hall","Picture a school hall packed shoulder to shoulder for an assembly. The people are the free electrons; the pillars bolted to the floor are the copper atoms.\n\n- **No electricity:** everyone shuffles about randomly, bumping into each other and the pillars. Lots of movement, but no one is *getting anywhere*. On average, as many people move left as right.\n- **Electricity flowing:** someone gently pushes from the back doors. Now, while still jostling, the whole crowd slowly edges towards the front. Almost at the same instant, someone near the front stage gets squeezed out of the front door.\n\nThe push travelled through the whole hall in a moment, even though each person only took a small step. Keep this picture; we will use it again in Chapter 3.",{"id":91,"type":86,"variant":92,"title":93,"markdown":94},"def-electricity","definition","Electricity, in one line","**Electricity** is the effect of electric charges, and an **electric current** is charge moving in one overall direction. In wires, the moving charges are free electrons; in salty water or in your body, they are charged atoms called **ions**.",{"id":96,"type":50,"title":97,"eyebrow":98,"navLabel":99},"ch-static","Charge that sits still, charge that flows","Chapter 02","2 Static and current",{"id":101,"type":43,"markdown":102,"help":103},"static-intro","There are two ways charge shows up in daily life, and the difference is simply whether it **stays put** or **keeps moving**.\n\n**Static electricity** happens when charge is moved from one object to another and then gets stuck there. Rub a balloon on dry hair and electrons hop from your hair onto the rubber. The balloon now has *extra* electrons (it is negatively charged) and your hair has *too few* (it is positively charged). Opposites attract, so the balloon clings to your hair or to a wall. Each strand of hair also carries the same charge as its neighbours, so the strands push apart and stand up.\n\n**Current electricity** is what runs your home: charge flowing steadily around a loop, again and again, carrying energy from a source (a battery, or a power station far away) to wherever it is needed.\n\nStatic is like water collected in a bucket on the roof. Current is like water flowing through a pipe with a pump keeping it moving.",{"simplerExplanation":104,"hints":105},"Static electricity is charge that has piled up in one place and stays there until it can jump away. Current electricity is charge that keeps flowing round a circuit.",[106,107],"Ask: is the charge sitting on something, or travelling round a loop?","A spark is the moment static charge suddenly stops being static.",{"id":109,"type":110,"caption":111,"columns":112,"rows":116},"static-table","table","Static electricity and current electricity side by side",[113,114,115],"Compare","Static electricity","Current electricity",[117,121,125,129,133],[118,119,120],"What the charge does","Builds up on a surface and stays there","Flows steadily round a closed loop",[122,123,124],"How it starts","Rubbing or separating two materials","A battery, solar cell or generator pushes it",[126,127,128],"How it ends","A sudden spark or a slow leak into damp air","Continues as long as the loop is closed and the source works",[130,131,132],"Everyday examples","Balloon on hair, crackling sweater, lift-button zap","Fan, phone charger, metro train",[134,135,136],"Useful?","Sometimes: photocopiers, laser printers, spray painting","Almost everything electric you own",{"id":138,"type":43,"markdown":139},"carpet-spark","Walk across a carpet in dry winter weather, touch a metal doorknob, and *snap*: a tiny spark and a sharp sting. As your feet rubbed the carpet, electrons were transferred and your body built up a charge. Your body is a fairly good conductor, so the charge spread over your skin, waiting. When your finger came near the metal, the charge found an easy path and jumped the last millimetre of air all at once.\n\nThat spark can involve **thousands of volts**, yet it is harmless because the *amount* of charge is tiny and it is gone in a fraction of a microsecond. (Volts are the \"push\"; you will meet them properly in the next layer.) It is a first hint of an important lesson: a big number of volts alone does not tell you how dangerous something is.\n\nWhy mostly in dry weather? Moist air slowly carries charge away from you before it can build up. In humid Mumbai in July you rarely get zapped; in dry Delhi in January, you often do.",{"id":141,"type":86,"variant":142,"title":143,"markdown":144},"tryit-balloon","try_it","The balloon and the tap","Blow up a balloon and rub it firmly on dry hair or a woollen sweater for 10 seconds.\n\n1. Hold it near small bits of torn paper. Watch them leap up.\n2. Turn on a kitchen tap to a very thin, steady trickle. Bring the balloon close to the stream without touching it. The water bends towards the balloon.\n3. Try again on a humid day, or after breathing on the balloon. The effect is weaker.\n\nThis is completely safe: the charge on a balloon is tiny. Never try \"static\" experiments near anything plugged into the wall.",{"id":146,"type":43,"markdown":147},"lightning","**Lightning is static electricity on a gigantic scale.** Inside a tall monsoon thundercloud, strong winds toss ice crystals and soft hail pellets up and down. When they collide, charge is scraped from one to the other, much like your balloon and hair. Lighter, positively charged ice crystals are carried to the top of the cloud; heavier, negatively charged pellets gather lower down.\n\nAir is normally a good insulator; it does not let charge through. But when enough charge separates, the push becomes so strong that the air itself breaks down and becomes a conductor for an instant. Charge rushes through the gap as a lightning flash, either within the cloud or between the cloud and the ground.",{"id":149,"type":62,"tone":150,"items":151},"lightning-spec","amber",[152,156,160,164],{"label":153,"big":154,"value":155},"Charge moved","≈ 5 C","A typical bolt moves about 5 coulombs, the charge of roughly 30 billion billion electrons.",{"label":157,"big":158,"value":159},"Current","10,000s A","For a split second the current reaches tens of thousands of amperes. A phone charger uses about 1–2 A.",{"label":161,"big":162,"value":163},"Duration","~0.03 s","The whole flash lasts only a few tens of thousandths of a second.",{"label":165,"big":166,"value":167},"Air temperature","≈ 28,000 °C","About 50,000 °F, several times hotter than the Sun's surface. The air expands so violently that we hear thunder.",{"id":169,"type":86,"variant":170,"title":171,"markdown":172},"aha-lightning","aha","The same idea, a trillion times bigger","The zap from a lift button and a lightning bolt over the Western Ghats are the same physics: charge separated by rubbing and collision, then a sudden rush through the air once the push is strong enough. The difference is scale. A doorknob spark moves a millionth of a coulomb or less; lightning moves millions of times more, with enough energy to split a tree.",{"id":174,"type":50,"title":175,"eyebrow":176,"navLabel":177},"ch-drift","Slow electrons, instant light","Chapter 03","3 Slow and fast",{"id":179,"type":180,"prompt":181,"options":182,"explanation":195},"predict-drift","prediction","You press the switch by your door. The bulb is about 3 metres of wire away. **How fast do you think the electrons in the wire actually move along it?**",[183,186,189,192],{"id":184,"label":185},"light","Close to the speed of light, 300,000 km every second",{"id":187,"label":188},"car","About as fast as a car on a highway",{"id":190,"label":191},"walk","About walking speed",{"id":193,"label":194},"snail","Slower than a snail: less than a millimetre per second","The surprising answer is the last one. In the wires of an ordinary circuit, the free electrons **drift** forward at only a fraction of a millimetre per second, typically around 0.1 to 0.3 mm\u002Fs, which is about 1 metre per hour. Yet the bulb lights the moment you press the switch. The rest of this chapter explains how both facts can be true at once.",{"id":197,"type":198,"diagram":199,"caption":200,"alt":201},"drift-diagram","diagram","electron-drift","Inside a copper wire: the copper atoms stay in place while free electrons zigzag about and, when a current flows, slowly drift one way.","A section of copper wire drawn as a regular grid of fixed copper atoms. Small blue dots representing free electrons are scattered between the atoms. Each electron follows a jagged, zigzag path as it bounces off atoms, but overall the whole group edges slowly in one direction along the wire. A label reads: copper atoms stay put, free electrons (blue) drift, this is a current.",{"id":203,"type":43,"markdown":204},"drift-explained","Look closely at one free electron. Even with no current at all, it is darting about at enormous speed, more than 1,000 kilometres **per second**, but in random directions, crashing into atoms and bouncing off billions of times a second. It is like a restless person in the hall crowd: always moving, going nowhere.\n\nWhen a battery is connected, it adds a gentle, steady push in one direction. Each electron still zigzags and collides, but between collisions it is nudged slightly forward. Averaged out, the whole crowd creeps along the wire. That slow average forward motion is the **drift speed**, and it really is tiny: in household wiring, well under a millimetre per second.\n\nSo how can a current be large enough to run a geyser if the electrons are so slow? Because there are so *many* of them. A slow-moving crowd that fills the whole width of a wide road can still move thousands of people past a gate every minute.",{"id":206,"type":86,"variant":170,"title":207,"markdown":208},"hose-full","The hose that is already full","Imagine a long garden hose that is **already full of water**. Open the tap and water comes out of the far end *immediately*, not because the water from the tap has raced to the end, but because the new water pushes on the water already in the hose, which pushes on the water in front of it, all the way to the nozzle.\n\nA wire is a hose that is always full of free electrons. When the switch closes, the *push* ripples along the whole wire at a large fraction of the speed of light (roughly two-thirds of it or more in ordinary cables), and electrons everywhere in the loop, including those already sitting inside the bulb, start drifting at almost the same instant. The electron that leaves the switch may take hours to reach the bulb; it does not matter, because the bulb's own electrons are already there.",{"id":210,"type":211,"title":212,"note":213,"scale":214,"rungs":215},"speed-ladder","ladder","How fast is fast? From drifting electrons to light","Each step up this ladder is a very large jump; the scale is logarithmic.","log",[216,220,224,228,232,236,240,244],{"label":217,"value":218,"display":219},"Electron drift in house wiring",0.00025,"≈ 0.25 mm\u002Fs",{"label":221,"value":222,"display":223},"A garden snail",0.001,"≈ 1 mm\u002Fs",{"label":225,"value":226,"display":227},"Walking to school",1.4,"≈ 1.4 m\u002Fs",{"label":229,"value":230,"display":231},"Car on a highway",25,"≈ 90 km\u002Fh",{"label":233,"value":234,"display":235},"Sound in air",343,"≈ 343 m\u002Fs",{"label":237,"value":238,"display":239},"An electron's random zigzag",1600000,"≈ 1,600 km\u002Fs",{"label":241,"value":242,"display":243},"The push travelling along a cable",200000000,"≈ 200,000 km\u002Fs",{"label":245,"value":246,"display":247},"Light in empty space",300000000,"≈ 300,000 km\u002Fs",{"id":249,"type":250,"title":251,"problem":252,"steps":253,"help":259},"we-drift","worked_example","How long would one electron take to reach the bulb?","The wire from a wall switch up to a ceiling bulb is **3 m** long. Suppose the electrons drift at **0.25 mm\u002Fs**. How long would a single electron take to travel from the switch to the bulb? And how long does the *push* take, if it travels at about 200,000 km\u002Fs?",[254,255,256,257,258],"Put both lengths in the same unit. 3 m = 3,000 mm.","Time for the electron = distance ÷ speed = 3,000 mm ÷ 0.25 mm\u002Fs = **12,000 seconds**.","Convert: 12,000 s ÷ 60 = 200 minutes = **3 hours 20 minutes**. Longer than a Bollywood film.","Now the push. 200,000 km\u002Fs = 200,000,000 m\u002Fs. Time = 3 m ÷ 200,000,000 m\u002Fs = 0.000000015 s, or **15 billionths of a second**.","Conclusion: the electron is hopelessly slow, but it does not need to arrive. The push reaches the bulb almost instantly and starts the electrons already inside it moving.",{"hints":260},[261,262],"Speed = distance ÷ time, so time = distance ÷ speed.","Make sure the distance and the speed use the same length unit before dividing.",{"id":264,"type":86,"variant":265,"title":266,"markdown":267},"limit-drift","model_limit","What the picture leaves out","The drift speed depends on the wire's thickness and how much current flows, so 0.25 mm\u002Fs is only a typical figure. In the alternating current from a wall socket (Chapter 6), electrons do not even travel steadily along; they wiggle back and forth by a tiny fraction of a millimetre, 50 times a second, and hardly get anywhere at all. Energy still reaches the bulb, because what travels along the wire is the push, not the electrons themselves.",{"id":269,"type":86,"variant":270,"title":271,"markdown":272},"misc-usedup","misconception","“The bulb uses up the electrons”","It is tempting to think electrons flow out of a battery, get \"used up\" in a bulb, and vanish. They do not. Every electron that leaves one end of the battery is matched by one returning to the other end. What the bulb uses is **energy** carried by the flow, not the electrons themselves. The electrons are more like the chain on a bicycle: the chain goes round and round unchanged, while the energy from your legs arrives at the back wheel.",{"id":274,"type":50,"title":275,"eyebrow":276,"navLabel":277},"ch-materials","Conductors, insulators and the clever in-betweens","Chapter 04","4 Materials",{"id":279,"type":43,"markdown":280,"help":281},"materials-intro","Whether charge can flow through something depends on how tightly its atoms hold their electrons.\n\n- **Conductors** have plenty of free charges that can move easily. Metals are the champions. Copper is used inside almost every wire in your house; aluminium, lighter and cheaper, is used in most overhead power lines.\n- **Insulators** hold their electrons tightly, so almost no charge can flow. Plastic (PVC) around wires, rubber, glass, porcelain, dry wood and dry air are all insulators.\n- **Semiconductors**, such as silicon, sit in between. On their own they conduct only a little, but by adding tiny traces of other elements, or by shining light on them, engineers can make them conduct exactly when and how they want. Every phone chip, LED and solar panel depends on this.\n\nLook at any wire in your home and you will find both kinds working as a team: a copper core to carry the flow, wrapped in plastic to keep it where it belongs.",{"simplerExplanation":282,"anotherExample":283},"Conductors let electricity through easily (metals). Insulators block it (plastic, rubber, glass). Semiconductors can be switched between the two, which is what makes computer chips possible.","A cable is like a water pipe: copper is the open inside of the pipe, and the plastic coating is the pipe wall that stops the water escaping.",{"id":285,"type":110,"caption":286,"columns":287,"rows":291},"materials-table","How some common materials behave",[288,289,290],"Material","Type","Where you meet it",[292,296,300,304,308,312,316,320,323,327],[293,294,295],"Silver","Excellent conductor (the best metal)","Tiny amounts in switch contacts and circuit boards; too costly for wiring",[297,298,299],"Copper","Excellent conductor","House wiring, motor coils, phone charger cables",[301,302,303],"Aluminium","Very good conductor, light","Overhead transmission lines across India",[305,306,307],"Graphite","Conductor (not a metal)","Pencil \"lead\", battery electrodes",[309,310,311],"Tap water, sea water, sweat","Conductor, because dissolved salts form ions","Wet hands, bathrooms, flooded streets",[313,314,315],"Silicon","Semiconductor","Phone and computer chips, solar panels",[317,318,319],"PVC plastic, rubber","Insulator","Wire coatings, switch covers, electrician's gloves",[321,318,322],"Glass, porcelain","The ribbed insulators that hold power lines on poles",[324,325,326],"Dry wood, paper","Insulator (poor when damp)","Furniture, notebooks",[328,329,330],"Dry air","Insulator, until the push is enormous","The gap in an open switch; broken down by lightning",{"id":332,"type":86,"variant":333,"title":334,"markdown":335},"careful-water","careful","Water and your body are conductors","Perfectly pure water conducts very poorly, but the water around us is never pure: tap water, rain puddles, sweat and seawater all contain dissolved salts, and those make it a conductor. Your body is mostly salty water, which is why it can carry a current and why electric shocks are dangerous.\n\nWet skin lets current into the body far more easily than dry skin. That is the scientific reason behind the rule you have heard all your life: **never touch switches, plugs or appliances with wet hands, and keep water away from anything plugged in.**",{"id":337,"type":86,"variant":338,"title":339,"markdown":340},"nuance-continuum","nuance","Not two boxes, but a long scale","\"Conductor\" and \"insulator\" are handy labels, but really every material sits somewhere on a very long scale. A good metal conducts roughly a billion billion times better than glass. Even an insulator will give way if the push is large enough; that is exactly what happens to air in a lightning strike, and why high-voltage power lines hang on long strings of porcelain discs rather than a single small one.",{"id":342,"type":86,"variant":142,"title":343,"markdown":344},"tryit-tester","Build a conductor tester (battery only)","You need a torch bulb or small LED in a holder, a 3 V pack of two AA cells, and three short wires. Connect battery → bulb → wire end A, and battery's other end → wire end B. Touch A and B together: the bulb lights, because you closed the loop.\n\nNow hold A and B against different objects: a steel spoon, a coin, a pencil's graphite tip (sharpen both ends), an eraser, a plastic ruler, aluminium foil, a wooden stick. Sort them into \"lights\" and \"doesn't light\".\n\nUse only batteries up to 9 V. **Never** use wires from a wall socket, extension board or appliance for any experiment.",{"id":346,"type":50,"title":347,"eyebrow":348,"navLabel":349},"ch-circuits","Circuits: the loop that must not break","Chapter 05","5 Circuits",{"id":351,"type":43,"markdown":352,"help":353},"circuit-intro","For current to flow, three things are needed:\n\n1. **A source of push**, such as a battery or the supply from the wall. It gives energy to the charges.\n2. **A complete, unbroken loop of conductor**, from one side of the source, out through whatever you want to power, and back to the other side of the source.\n3. **Something that uses the energy**, such as a bulb, a motor or a heater. (Engineers call this the load.)\n\nThe word *circuit* comes from the same root as *circle*. Charge must be able to go all the way round and return. If the path is broken at **any** point, even by a gap thinner than a hair, the flow stops everywhere in the loop at once. Remember the hose that is full of water: pinch it anywhere and the flow stops along its whole length, not just after the pinch.",{"simplerExplanation":354,"hints":355},"Electricity only flows if it can go out from the battery, through the bulb, and back to the battery in a full loop. Any gap stops it.",[356],"Trace the path with your finger. Can you get from one end of the battery back to the other without lifting your finger?",{"id":358,"type":359,"title":360,"items":361},"switch-steps","steps","What happens when you flip a switch",[362,366,370,374,378,382],{"title":363,"tag":364,"text":365},"Switch off: a gap in the loop","Open","Inside the switch, two metal contacts are pulled apart. The air gap between them is an insulator, so the loop is broken and no current flows anywhere in it.",{"title":367,"tag":368,"text":369},"You press the switch","Action","A spring snaps the contacts together quickly and firmly. A fast snap keeps sparking brief and the contacts from wearing out.",{"title":371,"tag":372,"text":373},"The loop is closed","Closed","Metal now touches metal. There is a complete conducting path from the supply, through the bulb, and back.",{"title":375,"tag":376,"text":377},"The push spreads","Instant","Within billionths of a second the push has run round the whole loop, and free electrons everywhere start drifting.",{"title":379,"tag":380,"text":381},"The bulb lights","Energy","Energy carried by the flow is turned into light (and some heat) inside the bulb. The electrons carry on round the loop.",{"title":383,"tag":364,"text":384},"Switch off again","The contacts spring apart, the gap reappears, and the flow stops everywhere at the same moment.",{"id":386,"type":86,"variant":270,"title":387,"markdown":388},"misc-switch","“The switch stores the electricity”","A switch does not store anything, and it does not \"send\" electricity. It is simply a gate in the loop: closed lets charge through, open blocks it. A switch on the far side of a bulb works just as well as one before it, because breaking the loop *anywhere* stops the current *everywhere*. (For safety reasons, electricians still put switches in the live wire, which you will learn about in a later layer.)",{"id":390,"type":180,"prompt":391,"options":392,"explanation":405},"predict-series","Two identical bulbs are wired one after the other in a single loop with a battery, so the current must pass through the first bulb to reach the second. **One bulb's thin wire filament snaps. What happens to the other bulb?**",[393,396,399,402],{"id":394,"label":395},"brighter","It gets brighter, because it now has all the electricity to itself",{"id":397,"label":398},"same","It stays exactly the same",{"id":400,"label":401},"dimmer","It gets a little dimmer",{"id":403,"label":404},"out","It goes out too","It goes out. The broken filament is a gap in the only loop there is, and a break anywhere stops the flow everywhere. This single-loop arrangement is called a **series** circuit. Try it in the lab below, then switch to the other arrangement, **parallel**, where each bulb has its own loop back to the battery.",{"id":407,"type":408,"component":409,"componentVersion":5,"config":410,"objective":415,"textAlternative":416,"help":417},"lab-one-bulb","interactive","circuit-lab",{"voltage":411,"bulbResistance":412,"bulbs":5,"mode":413,"allowModeChange":414},3,10,"series",false,"See that a single bulb lights only when there is a complete loop from the battery, through the bulb, and back.","The lab shows a 3 V battery (two AA cells) connected by wires to one bulb, forming a single loop. With the loop complete, the bulb glows and the lab reports a current of 0.3 A flowing all the way round, the same at every point in the loop. The bulb turns 0.9 W of electrical power into light and heat.\n\nIf the bulb is broken (its filament snapped), the loop has a gap. The lab then shows a current of 0 A everywhere, and the bulb is dark. Nothing about the battery changed; only the path did. The lesson: current needs a complete loop, and a gap anywhere stops it.",{"hints":418},[419,420],"Break the bulb and watch the current reading, not just the bulb.","Is the current different on the two sides of the bulb? (It never is in a single loop.)",{"id":422,"type":408,"component":409,"componentVersion":5,"config":423,"objective":426,"textAlternative":427,"help":428},"lab-two-bulbs",{"voltage":411,"bulbResistance":412,"bulbs":424,"mode":413,"allowModeChange":425},2,true,"Break one bulb in a series loop and see both go dark; then switch to parallel and see the other bulb keep shining.","The lab starts with a 3 V battery and two identical bulbs in **series**: one loop, bulb after bulb. Both glow, but each is dimmer than a single bulb would be: the current is 0.15 A, each bulb gets 1.5 V of the battery's push, and each gives out about 0.23 W (0.45 W in total).\n\nBreak one bulb in series and the current drops to 0 A. **Both bulbs go dark**, because the only path is broken.\n\nNow switch to **parallel**: each bulb sits on its own branch connected straight across the battery. Each bulb gets the full 3 V and 0.3 A, glowing as brightly as a single bulb (0.9 W each, 1.8 W in total, with 0.6 A drawn from the battery, so the battery runs down twice as fast). Break one bulb in parallel and only that branch stops; **the other bulb keeps shining** exactly as before.\n\nThis is why the lights and sockets in your home are wired in parallel: switching off the fan does not switch off the fridge.",{"simplerExplanation":429,"anotherExample":430,"hints":431},"Series is one loop, like a single-lane road: block it anywhere and everything stops. Parallel gives each bulb its own road back to the battery, so one broken bulb does not affect the other.","Old strings of festival lights were often wired in series: one dead bulb and the whole string went dark, and you had to test bulbs one by one to find the culprit. Your home's lights and sockets are wired in parallel.",[432,433],"First compare how bright the bulbs are in series and in parallel.","Then break one bulb in each arrangement and watch the other.",{"id":435,"type":86,"variant":170,"title":436,"markdown":437},"aha-parallel","Your house is one big parallel circuit","Every light, fan and socket in your home is connected across the supply on its own branch. That is why each has its own switch, why one blown bulb leaves the rest of the house lit, and why every appliance gets the same 230 V push. The next layers explain what happens to the total current as you switch on more and more branches, and why that is exactly what an MCB watches for.",{"id":439,"type":50,"title":440,"eyebrow":441,"navLabel":442},"ch-sources","A battery and a wall socket: two kinds of push","Chapter 06","6 Battery or socket",{"id":444,"type":43,"markdown":445},"sources-intro","Every circuit needs a source of push. In daily life you meet two very different kinds.\n\nA **battery** makes its push using chemistry. Inside, chemical reactions pile up electrons at one terminal (marked −) and pull them away from the other (+). Connect a loop and electrons flow out of the − end, round the loop, and back into the + end, always in the **same direction**. This one-way flow is called **direct current, DC**. Batteries are portable and fairly safe at low voltages, but they hold a limited amount of energy and must be recharged or replaced.\n\nA **wall socket** is the end of a very long chain of wires reaching back to generators in power stations, often hundreds of kilometres away. The push from the socket does not stay in one direction: it swings forward and backward, reversing again and again. This is **alternating current, AC**. In India the push completes **50 full back-and-forth cycles every second** (50 hertz), with a typical size of **230 volts**. In the USA and some other countries it is 120 V at 60 Hz.",{"id":447,"type":198,"diagram":448,"caption":449,"alt":450},"acdc-diagram","ac-dc-waves","DC gives a steady push in one direction; AC from an Indian socket swings positive and negative 50 times a second.","Two graphs of push against time. The top graph, labelled DC — battery, phone, laptop, is a flat horizontal line above zero: a steady push, always in one direction. The bottom graph, labelled AC — wall socket (50 Hz in India), is a smooth wave that rises above zero, falls below zero and rises again, showing two of the fifty cycles that happen in one second.",{"id":452,"type":62,"tone":453,"items":454},"source-spec","copper",[455,459,463,467,471],{"label":456,"big":457,"value":458},"AA cell","1.5 V DC","Remotes, clocks, torches. Safe to handle.",{"label":460,"big":461,"value":462},"Phone battery","≈ 3.7–3.9 V DC","A lithium-ion cell. Your charger turns mains AC into about 5 V DC (more for fast charging).",{"label":464,"big":465,"value":466},"Car or inverter battery","12 V DC","Stores far more energy than an AA cell. Can still cause burns and sparks if its terminals are shorted.",{"label":468,"big":469,"value":470},"Indian wall socket","230 V AC","50 Hz. Can kill. Never experiment with it.",{"label":472,"big":473,"value":474},"USA wall socket","120 V AC","60 Hz. Different plugs and appliances are built for each system.",{"id":476,"type":211,"title":477,"note":478,"scale":214,"rungs":479},"voltage-ladder","A ladder of pushes you meet in India","Voltage is the size of the push. Each rung is roughly several times the one below; the scale is logarithmic.",[480,483,486,490,494,498,502,506,510],{"label":456,"value":481,"display":482},1.5,"1.5 V",{"label":460,"value":484,"display":485},3.7,"≈ 3.7 V",{"label":487,"value":488,"display":489},"USB charger output",5,"5 V",{"label":491,"value":492,"display":493},"Square battery (PP3)",9,"9 V",{"label":495,"value":496,"display":497},"Car \u002F inverter battery",12,"12 V",{"label":499,"value":500,"display":501},"Home wall socket",230,"230 V",{"label":503,"value":504,"display":505},"Local line on the street poles",11000,"11 kV",{"label":507,"value":508,"display":509},"Railway and metro overhead wire",25000,"25 kV",{"label":511,"value":512,"display":513},"Big steel transmission towers",400000,"400 kV",{"id":515,"type":250,"title":516,"problem":517,"steps":518},"we-reversals","How often does the push from the socket change direction?","Indian mains is 50 Hz: 50 complete cycles every second. In each cycle, the push points one way, then the other. How many times does it **reverse direction** in one second, and in one minute?",[519,520,521,522],"One complete cycle contains two reversals: from forward to backward, and from backward to forward again.","Reversals per second = 50 cycles × 2 = **100 reversals every second**.","Reversals per minute = 100 × 60 = **6,000 reversals every minute**.","This is far too fast for your eyes to notice, which is why an LED bulb on AC mains looks perfectly steady.",{"id":524,"type":525,"itemId":526,"prompt":527,"check":528,"hints":533,"feedback":536},"practice-usa-hz","practice","electricity.discover-usa-reversals","Mains in the USA is 60 Hz. How many times per second does the push reverse direction there?",{"kind":529,"answer":530,"tolerance":531,"unit":532},"number",120,0,"reversals per second",[534,535],"Each complete cycle has two reversals.","Multiply the number of cycles per second by 2.",{"correct":537,"incorrect":538},"Yes: 60 cycles × 2 reversals per cycle = 120 reversals every second.","Each cycle has two reversals, so the answer is 60 × 2 = 120 reversals per second.",{"id":540,"type":86,"variant":333,"title":541,"markdown":542},"careful-mains","230 V is not a bigger battery","It is tempting to think the socket is \"just a stronger battery\". It is not. A 230 V supply pushes about 150 times harder than an AA cell, it is connected to a grid that can deliver enormous amounts of energy without running out, and it is able to drive a current through the human body that can stop the heart. All the hands-on activities in these lessons use batteries of 9 V or less. **Mains electricity is never an experiment.**",{"id":544,"type":43,"markdown":545},"why-ac-teaser","Why do homes use AC while phones and laptops use DC? The short answer is that AC is much easier to step **up** to very high voltages for long-distance travel and back **down** for safe use at home, using devices called transformers. Chips and batteries, meanwhile, need a steady one-way DC push, so every charger contains a small converter. You will explore how generators make AC and why the grid uses such enormous voltages in the deeper layers.",{"id":547,"type":50,"title":548,"eyebrow":549,"navLabel":550},"ch-day","A day that runs on it","Chapter 07","7 A day on power",{"id":552,"type":43,"markdown":553},"day-intro","Follow Ananya, a Class 8 student in a city apartment, through one ordinary weekday. Count how many moments depend on charge moving somewhere, often somewhere she cannot see.",{"id":555,"type":556,"title":557,"items":558},"day-timeline","timeline","One weekday, hour by hour",[559,563,567,571,575,579,583,587,591,595,599,603,607,611],{"time":560,"title":561,"text":562},"05:45","Phone alarm","The phone has been sipping about 5 V DC from its charger overnight. Its lithium-ion battery now runs the alarm, the screen and the radio that keeps it connected to the nearest mobile tower.",{"time":564,"title":565,"text":566},"06:00","Motor fills the tank","Downstairs, an electric pump lifts water to the rooftop tank. Without it, the taps on the upper floors would run dry within hours.",{"time":568,"title":569,"text":570},"06:20","Geyser for a bath","A 2,000 W geyser heats water by pushing current through a heating element: electricity turned straight into heat.",{"time":572,"title":573,"text":574},"06:40","Mixie and chutney","An electric motor spins the mixie blades at thousands of turns a minute. Electrical energy becomes movement.",{"time":576,"title":577,"text":578},"07:30","Metro to school","The train draws power from a 25 kV overhead wire (some lines use a 750 V third rail) and even feeds energy back when it brakes.",{"time":580,"title":581,"text":582},"08:30","Classroom","Ceiling fans, tube lights and a projector run from the school's supply. The school's water cooler keeps drinking water chilled.",{"time":584,"title":585,"text":586},"11:15","UPI at the canteen","A tap on a phone sends a message through a mobile tower to bank computers in data centres, all running on electricity, and back within a few seconds.",{"time":588,"title":589,"text":590},"13:00","Lunch from the fridge","The curd stayed fresh because a fridge's compressor pumped heat out of it all night.",{"time":592,"title":593,"text":594},"16:30","Traffic lights home","Signals, street cameras and the RO water purifier at home all depend on a steady supply.",{"time":596,"title":597,"text":598},"18:30","Street lights on","A light sensor switches on the LED street lights as the sun sets.",{"time":600,"title":601,"text":602},"19:00","The evening peak","Across India, millions of homes switch on lights, fans, TVs, coolers and ACs at once. This is when the grid is under the greatest strain.",{"time":604,"title":605,"text":606},"20:00","Homework online","The Wi-Fi router, laptop and a desk lamp hum along. The laptop's charger turns 230 V AC into about 20 V DC.",{"time":608,"title":609,"text":610},"21:30","Mosquito vaporiser","A small heater warms a liquid refill so it slowly evaporates through the night.",{"time":612,"title":613,"text":614},"22:30","Back on charge","The phone goes back on its charger, and the cycle starts again.",{"id":616,"type":86,"variant":617,"title":618,"markdown":619},"obs-invisible","observation","Count what you cannot see","Only some of Ananya's electricity was visible to her: the lamp, the mixie, the fan. Much of it happened out of sight: the pump in the basement, the mobile tower, the bank's computers, the substation near the metro line, the power station that may be burning coal or turning a turbine in a river hundreds of kilometres away. A modern day is held together by electricity flowing through places we never visit.",{"id":621,"type":622,"prompt":623},"reflect-day","reflection","Write down your own day in six to eight moments, from waking to sleeping. For each one, note what electricity was doing (making light, heat, motion, sound, or carrying information). Which moment would be hardest to live without?",{"id":625,"type":50,"title":626,"eyebrow":627,"navLabel":628},"ch-off","Now switch it all off","Chapter 08","8 Switch it all off",{"id":630,"type":43,"markdown":631},"off-intro","The best way to see how much we lean on electricity is to imagine it vanishing. Suppose the whole city's supply fails on a summer afternoon and does not come back. Some things stop at once; others hold on for a while on batteries, water tanks or diesel generators, then fail one by one.",{"id":633,"type":110,"caption":634,"columns":635,"rows":639},"off-table","A city without electricity: what fails, and roughly when",[636,637,638],"When","What fails","Why",[640,644,648,652,656],[641,642,643],"Instantly","Lights, fans, ACs, lifts, metro trains, traffic signals","They run directly on the supply and have no store of energy.",[645,646,647],"Within minutes","Wi-Fi and home internet (unless on an inverter); water purifiers; card machines without batteries","Routers and small devices lose power the moment the socket goes dead.",[649,650,651],"Within hours","Rooftop tanks run dry; fridges warm up; inverter and UPS batteries run flat; many mobile towers go quiet as backups run out","Stored water and stored cold last only a while; batteries hold a limited amount of energy.",[653,654,655],"Within a day","Phones die; ATMs and UPI stop working; petrol pumps cannot pump fuel","Every payment and fuel pump depends on electric computers and motors.",[657,658,659],"Within days","City water pumping and sewage treatment struggle; food spoils; hospitals depend on generators and diesel deliveries","Big backup generators need fuel, and fuel delivery itself depends on electric pumps and communication.",{"id":661,"type":86,"variant":338,"title":662,"markdown":663},"nuance-backup","Backups buy time, not a solution","Hospitals, mobile towers, data centres and airports have battery banks and diesel generators precisely because a power cut is so disruptive. But every backup is a *store* of energy, and stores run out. This is why grid operators work so hard to keep supply and demand balanced every second, and why a large blackout is treated as an emergency.",{"id":665,"type":180,"prompt":666,"options":667,"explanation":677},"predict-off","During a long power cut, a family keeps the fridge door shut. Roughly how long will it keep food reasonably cold?",[668,671,674],{"id":669,"label":670},"minutes","About 10 minutes",{"id":672,"label":673},"hours","A few hours",{"id":675,"label":676},"week","About a week","A few hours. The insulated walls of a fridge slow down heat leaking in, so a closed fridge stays cold for a few hours; opening the door lets the cold air spill out and shortens that time. The fridge has no power of its own: once the stored cold is gone, the food warms to room temperature.",{"id":679,"type":50,"title":680,"eyebrow":681,"navLabel":682},"ch-energy","Energy forms, and why electricity wins","Chapter 09","9 Energy forms",{"id":684,"type":43,"markdown":685},"energy-forms","Electricity is not a fuel you dig up. It is a way of **carrying energy** from where it is released to where you want it. Scientists call it a *secondary* source or an *energy carrier*: it has to be made from something else first, such as burning coal or gas, falling water, wind, sunlight or nuclear reactions.\n\nEnergy comes in many forms, and almost everything useful we do is turning one form into another. Electricity is special because it can be made from nearly every form and turned back into nearly every form.",{"id":687,"type":110,"caption":688,"columns":689,"rows":693},"energy-table","Forms of energy and how electricity connects to each",[690,691,692],"Form of energy","Everyday example","Link to electricity",[694,698,702,706,710,714,718],[695,696,697],"Chemical","Food, petrol, coal, a battery","Batteries turn chemical energy directly into electrical; coal is burned to make steam",[699,700,701],"Heat (thermal)","A hot tawa, steam from a pressure cooker","Power stations boil water to spin turbines; geysers and irons turn electricity back into heat",[703,704,705],"Kinetic (movement)","A spinning wheel, flowing river, wind","Generators turn movement into electricity; motors turn it back into movement",[707,708,709],"Light","Sunshine, a torch","Solar panels turn light into electricity; LEDs do the reverse",[711,712,713],"Sound","A song, a pressure-cooker whistle","Microphones turn sound into electrical signals; speakers turn them back",[715,716,717],"Gravitational (height)","Water held behind a dam, a rooftop tank","Hydro stations let water fall through turbines; electric pumps lift water up",[719,720,721],"Nuclear","The centre of the Sun, a reactor","Nuclear stations use the heat to make steam and spin generators",{"id":723,"type":724,"title":725,"prompt":726,"options":727},"energy-explorer","explorer","From source to switch","Pick a starting source and follow the energy all the way to a ceiling fan.",[728,742,753,762,770],{"id":729,"label":730,"chain":731,"badge":738,"note":741},"coal","Coal",[732,733,734,735,736,737],"Coal burns","Heat boils water","Steam spins turbine","Generator","Grid wires","Fan motor",{"text":739,"tone":740},"Releases CO₂","no","Coal still makes the largest share of India's electricity. Burning it releases carbon dioxide, and much of the heat is lost along the way: only about a third of the coal's energy typically becomes electricity.",{"id":743,"label":744,"chain":745,"badge":749,"note":752},"hydro","Falling water",[746,747,748,735,736,737],"Water behind a dam","Water falls","Turbine spins",{"text":750,"tone":751},"No fuel burned","yes","Hydro stations, from the Bhakra dam to smaller plants in the hills, use the energy of water falling from a height. No fuel is burned, although dams change rivers and the land around them.",{"id":754,"label":755,"chain":756,"badge":760,"note":761},"sun","Sunlight",[755,757,758,759,736,737],"Silicon solar panel","DC electricity","Inverter makes AC",{"text":750,"tone":751},"Solar panels turn light into electricity directly, with no moving parts, using the semiconductor silicon. India has added solar capacity very fast; its limitation is that it only works when the sun shines.",{"id":763,"label":764,"chain":765,"badge":768,"note":769},"wind","Wind",[766,767,735,736,737],"Moving air","Blades turn",{"text":750,"tone":751},"Wind farms in states such as Tamil Nadu and Gujarat turn moving air into electricity. Output rises and falls with the wind, so the grid has to balance it with other sources.",{"id":771,"label":772,"chain":773,"badge":775,"note":777},"battery","Battery",[774,758,737],"Chemicals in a cell",{"text":776,"tone":740},"Stores, does not make","A battery-powered fan skips the grid. But a rechargeable battery is only a store: the energy in it was put there earlier, usually from a wall socket.",{"id":779,"type":43,"markdown":780},"why-convenient","Why has electricity become the way we deliver energy to almost everything? Compare it with carrying coal to every home, or a gas cylinder to every fan.\n\n- **It travels almost instantly** through thin wires over hundreds of kilometres, with no trucks, pipes or storage at each house.\n- **It turns into almost anything**: heat in a geyser, motion in a fan, light in an LED, sound in a speaker, and information in a phone.\n- **It is precisely controllable**: a switch, a regulator or a chip can turn it on, off or down in a fraction of a second.\n- **It is clean where you use it**: no smoke in the kitchen, no ash, no fumes from a fan.\n\nIt has two big weaknesses. It is hard to **store** in large amounts, so power stations must make it at the very moment it is used. And it is only as clean as the way it was **made**: an electric scooter charged from coal still causes emissions, just at the power station instead of at the tailpipe.",{"id":782,"type":86,"variant":333,"title":783,"markdown":784},"careful-clean","Clean at the switch, not always at the source","\"Electric\" does not automatically mean \"pollution-free\". Ask where the electricity came from. Power from solar, wind, hydro or nuclear stations releases very little carbon dioxide while running; power from coal releases a lot. The same fan can have a very different environmental cost depending on the grid it is plugged into.",{"id":786,"type":50,"title":787,"eyebrow":788,"navLabel":789},"ch-safety","First safety rules","Chapter 10","10 Safety first",{"id":791,"type":43,"markdown":792},"safety-intro","Everything in this layer points to one uncomfortable fact: **your body is a conductor**, and a wall socket or power line can push a dangerous current through it. A current too small to light a torch bulb, only a few hundredths of an ampere, can upset the rhythm of the heart if it passes through the chest. Electricity gives no warning: it has no smell, no sound, and a live wire looks exactly like a dead one.\n\nThe good news is that a handful of rules prevent almost all accidents. They are worth knowing by heart.",{"id":794,"type":359,"title":795,"items":796},"safety-steps","Rules to live by",[797,801,804,807,811,814,818,822],{"title":798,"tag":799,"text":800},"Never poke into sockets","Home","No fingers, pins, keys or wires in a socket, ever. Use socket covers where small children live.",{"title":802,"tag":799,"text":803},"Keep water and electricity apart","Dry your hands before touching switches or plugs. Never use a hair dryer or phone on charge near a bucket, tub or wet floor.",{"title":805,"tag":799,"text":806},"Pull the plug, not the cord","Tugging the wire loosens connections and damages insulation. Replace cracked plugs and frayed wires; tape is not a repair.",{"title":808,"tag":809,"text":810},"Stay away from fallen lines","Outdoors","Treat every fallen or sagging wire as live. Keep well back, keep others away, and call the electricity company's helpline. Never touch a person stuck to a live wire.",{"title":812,"tag":809,"text":813},"Kites far from wires","Fly kites only in open spaces away from lines. If a kite snags on a wire, let it go. Metallic or wet manja can conduct and has caused deadly shocks.",{"title":815,"tag":816,"text":817},"Beware flooded streets","Monsoon","During heavy rain, avoid walking near electric poles, transformers and street-light boxes; water can become live if a wire falls into it.",{"title":819,"tag":820,"text":821},"Get indoors in a storm","Lightning","If you can hear thunder, lightning is close enough to strike. Go inside a building or a closed car, and do not shelter under a lone tree.",{"title":823,"tag":824,"text":825},"Leave repairs to electricians","Always","Anything behind a switch plate, inside an appliance or on a pole is a job for a qualified electrician, with the supply switched off at the MCB.",{"id":827,"type":86,"variant":333,"title":828,"markdown":829},"careful-rescue","If someone gets a shock","Do **not** grab them: the current can pass through you too. First cut the power at the switch or MCB if you can do so safely. If you cannot, push them away from the source with something dry that does not conduct, such as a wooden broom handle or a plastic chair, while standing on something dry. Then call for help (112 in India) and get medical care, even if they seem fine.",{"id":831,"type":250,"title":832,"problem":833,"steps":834,"help":839},"we-thunder","How far away is the storm?","You see a flash of lightning and count **6 seconds** before you hear the thunder. Light arrives almost instantly; sound travels at about **343 m\u002Fs**. How far away was the lightning?",[835,836,837,838],"Distance = speed × time.","Distance ≈ 343 m\u002Fs × 6 s = **2,058 m**, about 2 km.","A quick rule: every 3 seconds of counting is roughly 1 km.","Lightning can strike more than 10 km from the storm that made it, so 2 km is well within reach. Time to be indoors.",{"hints":840},[841,842],"Light from the flash reaches you almost immediately, so the delay is all due to the slower sound.","Multiply the speed of sound by the number of seconds you counted.",{"id":844,"type":86,"variant":617,"title":845,"markdown":846},"fact-lightning-india","Lightning in India","Lightning kills more people in India than any other force of nature. The National Crime Records Bureau counted **2,560 lightning deaths in 2023** and 2,887 in 2022, with Madhya Pradesh, Bihar, Odisha, Uttar Pradesh and Jharkhand worst affected. Most of these deaths are preventable by getting indoors when thunder is heard and staying away from tall isolated trees, open fields and water during a storm.",{"id":848,"type":50,"title":849,"eyebrow":850,"navLabel":851},"ch-check","Check yourself, and what comes next","Chapter 11","11 Quiz and next",{"id":853,"type":853,"title":854,"questions":855},"quiz","Discover quiz: charge on the move",[856,873,889,906,920,937,953,970],{"itemId":857,"prompt":858,"options":859,"correct":867,"why":872},"electricity.discover-what-moves","In a copper wire carrying a current, what actually moves along the wire?",[860,863,866,869],{"id":861,"label":862},"protons","Protons",{"id":864,"label":865},"atoms","Whole copper atoms",{"id":867,"label":868},"electrons","Free electrons",{"id":870,"label":871},"nothing","Nothing moves; only energy does","Copper atoms (with their protons) stay fixed in place. Some of each atom's outer electrons are free to wander, and it is these free electrons that drift along the wire when a current flows.",{"itemId":874,"prompt":875,"options":876,"correct":878,"why":888},"electricity.discover-balloon","After you rub a balloon on dry hair, it sticks to the wall. What has happened to the balloon?",[877,880,882,885],{"id":878,"label":879},"gained","It has gained extra electrons and become negatively charged",{"id":861,"label":881},"It has gained extra protons",{"id":883,"label":884},"magnet","It has become magnetic",{"id":886,"label":887},"current","A current is flowing through it","Rubbing moves electrons from the hair to the rubber. The balloon now carries extra negative charge that stays put (static electricity). Protons are locked in nuclei and do not move from one object to another.",{"itemId":890,"prompt":891,"options":892,"correct":897,"why":905},"electricity.discover-instant-light","Electrons drift at well under 1 mm\u002Fs, yet a bulb lights the instant you press the switch. Why?",[893,896,899,902],{"id":894,"label":895},"fast","Electrons speed up hugely when the switch is pressed",{"id":897,"label":898},"full","The wire is already full of free electrons, and the push travels round the loop almost at light speed",{"id":900,"label":901},"stored","The bulb stores electricity from last time",{"id":903,"label":904},"sound","The switch sends a sound wave to the bulb","Like water in a full hose, the electrons are everywhere in the circuit already. Closing the switch sends the push around the loop at a large fraction of the speed of light, so electrons inside the bulb start moving almost at once.",{"itemId":907,"prompt":908,"options":909,"correct":915,"why":919},"electricity.discover-insulator","Which of these is an insulator?",[910,911,914,917],{"id":453,"label":297},{"id":912,"label":913},"salty","Salty water",{"id":915,"label":916},"pvc","PVC plastic",{"id":918,"label":305},"graphite","PVC holds its electrons tightly, so almost no charge can flow through it. That is why it is used to coat wires. Copper and graphite conduct, and salty water conducts because its dissolved salts form moving ions.",{"itemId":921,"prompt":922,"options":923,"correct":925,"why":936},"electricity.discover-series-break","Three bulbs are wired in series with a battery. One bulb breaks. What happens?",[924,927,930,933],{"id":925,"label":926},"all-out","All three go out",{"id":928,"label":929},"two-on","The other two stay on at the same brightness",{"id":931,"label":932},"two-bright","The other two get brighter",{"id":934,"label":935},"one-out","Only the broken bulb goes out","In series there is only one loop. A broken filament is a gap in that loop, and a gap anywhere stops the current everywhere, so every bulb goes dark.",{"itemId":938,"prompt":939,"options":940,"correct":945,"why":952},"electricity.discover-ac-dc","Which statement about the supply in an Indian home is correct?",[941,944,947,950],{"id":942,"label":943},"dc230","It is 230 V DC",{"id":945,"label":946},"ac230","It is 230 V AC at 50 Hz, reversing direction 100 times a second",{"id":948,"label":949},"ac120","It is 120 V AC at 60 Hz",{"id":397,"label":951},"It is the same kind of push as a phone battery, only bigger","Indian mains is alternating current at about 230 V and 50 Hz. Each cycle has two reversals, so the push reverses 100 times a second. 120 V at 60 Hz is used in the USA. A battery gives steady one-way DC.",{"itemId":954,"prompt":955,"options":956,"correct":961,"why":969},"electricity.discover-secondary","Why is electricity called a secondary energy source (an energy carrier)?",[957,960,963,966],{"id":958,"label":959},"second","Because it was discovered after fire",{"id":961,"label":962},"made","Because it must be made from another source, such as coal, water, wind or sunlight",{"id":964,"label":965},"weak","Because it is weaker than other forms of energy",{"id":967,"label":968},"two","Because it needs two wires","We cannot dig electricity out of the ground. It is produced by converting a primary source (chemical, kinetic, light or nuclear energy) and then carried to where it is used.",{"itemId":971,"prompt":972,"options":973,"correct":984,"why":986},"electricity.discover-kite","Your kite gets tangled in an overhead electric line. What should you do?",[974,977,980,983],{"id":975,"label":976},"pull","Pull the string hard to free it",{"id":978,"label":979},"stick","Knock it down with a long metal pole",{"id":981,"label":982},"climb","Climb the pole carefully while wearing rubber slippers",{"id":984,"label":985},"leave","Let go of the string, leave the kite, and stay away from the line","Manja, especially wet or metallic manja, can conduct, and metal poles certainly do. Rubber slippers do not make climbing safe. No kite is worth the risk: let it go and keep away from the line.",{"id":988,"type":43,"markdown":989},"teaser-vir","You now have the picture: charges already sitting in every wire, a push that sets them drifting round a complete loop, and energy delivered wherever the loop passes through a bulb, fan or heater.\n\nIn the next layer, *Understand*, that picture gets three precise names and units, using the water in a rooftop tank, a pump and pipes as a guide:\n\n- **Voltage** (volts, V): how hard the source pushes, like the pressure from a pump.\n- **Current** (amperes, A): how much charge flows past a point each second, like litres of water per second.\n- **Resistance** (ohms, Ω): how much a part of the circuit opposes the flow, like a narrow section of pipe.\n\nYou will see how the three are linked, why a thin geyser element gets hot, and how to read the numbers printed on your own appliances.",{"id":991,"type":992,"title":993,"points":994},"cheat-sheet","summary","Cheat sheet",[995,996,997,998,999,1000,1001,1002,1003,1004,1005,1006,1007],"**Electricity is charge on the move.** All matter contains positive protons and negative electrons, normally balanced.","Opposite charges attract; like charges repel.","In metals, some electrons are **free** and wander between fixed atoms. A current is these free electrons drifting one way.","**Static electricity** is charge stuck on a surface (balloon, carpet spark, lightning). **Current electricity** is charge flowing round a loop.","A typical lightning bolt moves about 5 C of charge in a few hundredths of a second and heats air to about 28,000 °C.","Electrons **drift** at well under 1 mm\u002Fs, but the **push** travels round a circuit at a large fraction of the speed of light, like water in a hose that is already full.","**Conductors** (copper, aluminium, salty water, your body) let charge flow; **insulators** (PVC, rubber, glass, dry air) block it; **semiconductors** (silicon) can be controlled.","A **circuit** needs a source, a complete loop and a load. A switch opens or closes a gap. A break anywhere stops the flow everywhere.","**Series**: one loop, one broken bulb stops all. **Parallel**: separate branches, as in your home's wiring.","**DC** (batteries) pushes one way. **AC** (Indian sockets: 230 V, 50 Hz; USA: 120 V, 60 Hz) reverses 100 times a second in India.","Electricity is an **energy carrier**: made from coal, water, wind, sun or nuclear energy, and turned into heat, light, motion and sound.","Safety: nothing in sockets, keep water away, never touch fallen lines, let snagged kites go, get indoors when you hear thunder. Experiments use batteries of 9 V or less only.","Coming next: **voltage** (push, V), **current** (flow, A) and **resistance** (opposition, Ω).",{"id":1009,"type":1009,"sourceIds":1010},"sources",[1011,1012,1013,1014,1015,1016,1017,1018,1019],"elec-discover-pc-electric-current","elec-discover-pc-circuit-requirements","elec-discover-pc-conductors-insulators","elec-discover-nist-ampere","elec-discover-nssl-lightning","elec-discover-nws-lightning-safety","elec-discover-eia-electricity","elec-discover-esf-home-safety","elec-discover-ncrb-lightning",[1011,1012,1013,1014,1015,1016,1017,1018,1019],"needs_review",{"generatedBy":1023,"notes":1024},"claude-code","Draft generated locally; pending owner review.","950a6a778ba679dd16619fa2dc12e146aa57dff477f3f0e89e3b8153cbfc6e58",{"diagram:electron-drift":1027,"component:circuit-lab@1":1028,"diagram:ac-dc-waves":1029,"logic:practice":1030,"source:elec-discover-eia-electricity":1031,"source:elec-discover-esf-home-safety":1032,"source:elec-discover-ncrb-lightning":1033,"source:elec-discover-nist-ampere":1034,"source:elec-discover-nssl-lightning":1035,"source:elec-discover-nws-lightning-safety":1036,"source:elec-discover-pc-circuit-requirements":1037,"source:elec-discover-pc-conductors-insulators":1038,"source:elec-discover-pc-electric-current":1039},"622d4829bbf48216aac7636fc97ed517e2238dfc2f9f75382d80734e72120ee5","20ac7be2c5201768a46360df1d470c51d9dd2633c0d59a7e6848a8b646ee82e4","f44677a81e3cf0d5be75c8c3a956c038d3e8b174c2bf253c3c6109679a987ba6","3d6b0fe1b15255975a32b0fcd94e8019bc959ad45cbf12e136e86149549c6878","f28b677ab1a2f0c112a6bbf0ffe3f85b9e4ef4e9cd526e71d32fc47184b56f84","8de0ae46ea06a2471676ffdd1ac453ca5c67907443ca43617cde518f0ff65494","e7bf25334d9bde899bc933f4bcda2e948b2e3d6515f84515d36f991bead0e17a","3d085e3f69739e0a40a1f4931af5cd6313e766be63374233866b87501cf7a4f1","be0532d470bdc994d593ce6bda372b4c88793c3f1cf5d83670dd0f142abaed0e","a9e53bea7b49ef9c73502f5f023489d7f49a76993722d5f0c295e3c40ff82902","279be81b24e528384836308be602c776e2440207a6b9a95dbcca5bf33b2d8075","724bb44faa181b8bc669649d96e8f62a6b0d2880d6cc34cc9c77c2ff9af07afe","20b9bdc9082d7bd9d6607b37a5b2205ae193861c72444f7d1c41ad06c1ca5acc",{"state":1041,"reviewer":1042,"selfReview":425,"reviewedAt":1043,"method":1044},"approved","The library owner","2026-09-20T10:18:37.581Z","owner_bulk","preview-7e1cbbcc4f",1789899599697]