[{"data":1,"prerenderedAt":947},["ShallowReactive",2],{"layer:electricity:deepen":3},{"layer":4,"contentHash":923,"dependencyHashes":924,"approval":940,"releaseId":946},{"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":918,"reviewStatus":919,"authoring":920},1,"electricity","en","deepen","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.",[13,14,15,16,17],"Explain electromagnetic induction and use f = rpm × (poles ÷ 2) ÷ 60 to find a generator's frequency.","Compare AC and DC and describe how coal, hydro, nuclear, wind and solar stations make electricity.","Trace the journey from generator to socket and use P = V × I and loss = I²R to show why transmission uses high voltage.","Use the turns ratio Vs ÷ Vp = Ns ÷ Np and energy E = P × t (in kWh) in simple calculations.","Explain why grid frequency shows the balance between supply and demand, and describe India's generation mix.",35,{"title":20,"rows":21},"Rating plate",[22,25,28,31,34,37],{"label":23,"value":24},"Depth","Go deeper",{"label":26,"value":27},"Reading time","About 35 minutes",{"label":29,"value":30},"Prior knowledge","Voltage, current, resistance; a little about magnets",{"label":32,"value":33},"Labs","Generator: two-pole and four-pole",{"label":35,"value":36},"Chapters","11",{"label":38,"value":39},"Units used","V, kV, A, Ω, W, MW, Hz, rpm, kWh",[41,45,48,54,57,66,72,77,114,119,122,138,156,172,177,180,192,206,211,216,219,225,250,256,260,265,270,273,335,339,344,353,358,361,401,451,455,459,464,473,488,501,516,531,535,539,544,553,558,570,580,593,597,601,606,612,626,636,649,653,658,664,684,687,692,696,701,704,743,747,752,886,903],{"id":42,"type":43,"markdown":44},"intro-switch","prose","Flick on a ceiling fan in Pune or Patna and it starts turning almost at once. Somewhere, possibly hundreds of kilometres away, a machine the size of a railway carriage is spinning 50 times a second, and a tiny share of its output has just been sent to your fan.\n\nYou have already met voltage (the push), current (the flow) and resistance (what gets in the way). This layer asks the bigger questions: **where does the push come from in the first place, and how does it travel all that way without most of it being lost?**",{"id":46,"type":43,"markdown":47},"intro-map","The story has three parts.\n\n1. **Making it.** Almost every power station on Earth, whether it burns coal, splits uranium or catches the wind, uses the same trick discovered in 1831: move a magnet near a coil of wire and a current appears. Solar panels are the big exception.\n2. **Moving it.** Electricity leaves the station, gets its voltage raised enormously, races across the country on tall steel towers, and is stepped down again, several times, before it reaches your street.\n3. **Balancing it.** Electricity is hard to store in bulk, so the grid has to make exactly as much as everyone uses, second by second. The frequency of the grid, 50 Hz in India, is the tell-tale sign of whether that balance is being kept.",{"id":49,"type":50,"title":51,"eyebrow":52,"navLabel":53},"ch01","chapter","Faraday's discovery: a changing magnet pushes charge","Chapter 01","1 Faraday's push",{"id":55,"type":43,"markdown":56},"faraday-story","In 1820 the Danish scientist Hans Christian Ørsted noticed that a wire carrying current made a nearby compass needle swing. Electricity could make magnetism. The obvious question followed: **could magnetism make electricity?**\n\nFor years people tried and failed. They put strong magnets next to coils of wire and waited. Nothing happened. In 1831 Michael Faraday, working at the Royal Institution in London, found out why. He wound two separate coils of wire around an iron ring. When he switched on a battery connected to the first coil, a needle attached to the second coil gave a brief kick, then settled back to zero. When he switched the battery off, it kicked again, the other way.\n\nThe current in the second coil only appeared **while the magnetism was changing**. A steady magnet, however strong, does nothing. A changing one pushes charge.",{"id":58,"type":43,"markdown":59,"help":60},"faraday-magnet-coil","Faraday soon showed the same thing with nothing but a bar magnet and a coil. Push the magnet into the coil and a current flows one way. Hold it still inside and the current stops. Pull it out and the current flows the other way.\n\nHe noticed three things that made the push (the induced voltage) bigger:\n\n- **Move faster.** The quicker the magnetic field inside the coil changes, the bigger the push.\n- **Use more turns.** Every loop of wire gets its own small push, and they add up. A coil of 500 turns gets 500 times the push of a single loop.\n- **Use a stronger magnet.** More magnetic field means more field to change.\n\nThat is **electromagnetic induction**, and it is the heart of this whole layer. The rule in words: *the induced voltage depends on how fast the magnetic field through the coil changes, multiplied by the number of turns.*",{"simplerExplanation":61,"anotherExample":62,"hints":63},"A magnet sitting still next to a wire does nothing. A magnet moving near a wire gives the charges in the wire a shove. Faster movement means a bigger shove.","A bicycle dynamo works this way. The wheel spins a small magnet inside a coil. Ride slowly and the lamp is dim; ride fast and it gets bright, because the magnet's field is changing faster.",[64,65],"Ask: is the magnetic field through the coil changing right now? If not, there is no push.","Speed, number of turns and magnet strength all make the push bigger.",{"id":67,"type":68,"variant":69,"title":70,"markdown":71},"aha-change","callout","aha","It is the change that matters","The strongest magnet in the world, sitting perfectly still inside a coil, produces **zero** voltage. A weak magnet waved about quickly produces some. This is why every generator spins: spinning keeps the magnetic field through the coils changing, over and over, forever.",{"id":73,"type":68,"variant":74,"title":75,"markdown":76},"lenz-careful","nuance","Why it is hard work to spin a generator","When the induced current flows, it makes its own magnetic field, and that field always pushes back against the motion that caused it (this is **Lenz's law**). Spin a generator with nothing connected and it turns easily. Connect a bulb and it suddenly gets harder to turn. You are now doing real work, and that work becomes the energy in the bulb. Nothing is free: a power station must burn more fuel, or let more water through, when more people switch things on.",{"id":78,"type":79,"title":80,"items":81},"timeline-history","timeline","From a twitching needle to a national grid",[82,86,90,94,98,102,106,110],{"time":83,"title":84,"text":85},"1820","Ørsted's compass","A current in a wire deflects a compass needle. Electricity can make magnetism.",{"time":87,"title":88,"text":89},"1831","Faraday's induction","Faraday shows that a **changing** magnetic field induces a current, using an iron ring with two coils and then a magnet and coil. He also builds a spinning copper disc generator.",{"time":91,"title":92,"text":93},"1832","First hand-cranked generator","Hippolyte Pixii in Paris spins a magnet near coils with a hand crank and gets alternating current.",{"time":95,"title":96,"text":97},"1882","Power stations for cities","Edison's Pearl Street station in New York begins supplying 110 V DC to customers in the surrounding district. Low-voltage DC could not be sent far, which is why stations had to sit among the homes they served.",{"time":99,"title":100,"text":101},"1891","Long-distance AC","A three-phase AC line carries power about 175 km from Lauffen to Frankfurt in Germany, showing that transformers and high voltage beat DC for distance.",{"time":103,"title":104,"text":105},"1897","Hydro in Darjeeling","The Sidrapong hydroelectric station near Darjeeling, one of the first in India, starts supplying the town.",{"time":107,"title":108,"text":109},"1902","Shivanasamudra","A hydro station on the Kaveri in Karnataka sends power to the Kolar gold fields about 150 km away.",{"time":111,"title":112,"text":113},"2013","One nation, one grid","On 31 December 2013 the southern grid is joined to the rest by a 765 kV line, so all of mainland India runs as one synchronous grid at 50 Hz.",{"id":115,"type":50,"title":116,"eyebrow":117,"navLabel":118},"ch02","Spin a generator: speed sets voltage and frequency","Chapter 02","2 Spin a generator",{"id":120,"type":43,"markdown":121},"generator-anatomy","A power-station generator is Faraday's magnet and coil, scaled up and organised.\n\n- The **rotor** is a huge spinning electromagnet on a steel shaft.\n- The **stator** is a stationary cylinder of heavy copper coils wrapped around the rotor.\n- A **turbine** on the same shaft is pushed round by steam, water or wind.\n\nAs the rotor turns, its north pole sweeps past a coil, then its south pole. The field through each coil rises, falls, reverses and comes back. So the push on the charges rises, falls, **reverses**, and comes back. The generator naturally makes **alternating current**, AC.\n\nOne full turn of a two-pole rotor (one north, one south) gives one complete wave: push one way, then the other. That complete wave is called a **cycle**, and the number of cycles each second is the **frequency**, measured in hertz (Hz).",{"id":123,"type":124,"items":125},"formulas-generator","formulas",[126,129,132,135],{"expression":127,"caption":128},"f = rpm × (poles ÷ 2) ÷ 60","Frequency in Hz of an ideal generator. poles ÷ 2 is the number of pole pairs; ÷ 60 turns revolutions per minute into per second.",{"expression":130,"caption":131},"3,000 rpm, 2 poles → 50 Hz","India's grid frequency from a two-pole machine: 3,000 × 1 ÷ 60 = 50.",{"expression":133,"caption":134},"1,500 rpm, 4 poles → 50 Hz","Twice the poles, half the speed, same frequency: 1,500 × 2 ÷ 60 = 50.",{"expression":136,"caption":137},"voltage ∝ speed","For a fixed magnet and coil, peak voltage rises in proportion to how fast the rotor turns.",{"id":139,"type":140,"prompt":141,"options":142,"explanation":155},"predict-generator","prediction","A two-pole generator is spinning at 1,500 rpm, half of its normal 3,000 rpm. What happens to its output compared with normal?",[143,146,149,152],{"id":144,"label":145},"a","Same voltage, half the frequency",{"id":147,"label":148},"b","Half the voltage, same frequency",{"id":150,"label":151},"c","Half the voltage and half the frequency",{"id":153,"label":154},"d","Nothing changes; only the magnet matters","**Both halve.** The frequency is simply how many times the poles sweep past each coil per second, so half the speed gives 25 Hz instead of 50 Hz. The voltage depends on how fast the field through the coils changes, so half the speed also means half the push. Test it in the lab below.",{"id":157,"type":158,"component":159,"componentVersion":5,"config":160,"objective":164,"textAlternative":165,"help":166},"lab-generator-2pole","interactive","generator",{"initialRpm":161,"poles":162,"gridHz":163},600,2,50,"Change the rotor speed and see how the output frequency and voltage change, and find the speed that matches India's 50 Hz grid.","This lab shows a two-pole generator with a speed slider from 0 to 3,600 revolutions per minute (rpm), a wave graph of the output voltage, readouts of frequency and voltage, and a bulb.\n\nIt starts at 600 rpm. The frequency is 600 × 1 ÷ 60 = **10 Hz**, and the peak voltage is only 20% of its value at grid speed, because 10 is 20% of 50. The bulb is dim and visibly flickers, because the current reverses 20 times a second and the filament has time to cool a little between peaks.\n\nAt 1,500 rpm the frequency is **25 Hz** and the voltage is 50% of grid value. The bulb is brighter; the flicker is harder to see.\n\nAt **3,000 rpm** the frequency is **50 Hz**, exactly India's grid frequency, and the voltage is 100%. The waves on the graph are packed five times closer than at 600 rpm and are five times taller. The bulb glows steadily.\n\nAt 3,600 rpm the frequency is **60 Hz**, the grid frequency used in the USA, and the voltage is 120% of the 50 Hz value.\n\nAt 0 rpm there is no wave at all: no change, no voltage. The pattern: frequency and voltage both rise in direct proportion to speed.",{"simplerExplanation":167,"anotherExample":168,"hints":169},"Spin faster and two things go up together: how often the current flips direction (frequency) and how hard it pushes (voltage).","Pedal a bicycle dynamo slowly and the lamp is dim and flickery. Pedal hard and it is bright and steady. Same physics, smaller machine.",[170,171],"Divide the rpm by 60 to get turns per second. For a two-pole machine, that is also the frequency.","Try to land exactly on 50 Hz. What rpm did you need?",{"id":173,"type":68,"variant":174,"title":175,"markdown":176},"flicker-observation","observation","Why the bulb flickers at low speed","A filament bulb on AC actually gets brighter and dimmer twice every cycle, because it heats up whenever current flows, whichever direction it goes. At 50 Hz that happens 100 times a second, too fast for the filament to cool or for your eyes to notice. At 10 Hz it happens only 20 times a second, and you can see the shimmer.",{"id":178,"type":43,"markdown":179},"four-pole-prose","What if you want 50 Hz but your turbine prefers to turn more slowly? Add more poles. A rotor with **four poles** (north, south, north, south) sends two complete waves past each coil in every turn. So it only needs to spin at **1,500 rpm** to make 50 Hz.\n\nHydroelectric generators take this idea much further. Water turbines turn slowly, so their rotors have dozens of poles arranged around a wide wheel. A 40-pole hydro generator makes 50 Hz at just 150 rpm.",{"id":181,"type":158,"component":159,"componentVersion":5,"config":182,"objective":185,"textAlternative":186,"help":187},"lab-generator-4pole",{"initialRpm":183,"poles":184,"gridHz":163},1500,4,"Compare a four-pole generator with a two-pole one and find the speed that gives 50 Hz with four poles.","This lab is the same generator but with a four-pole rotor. It starts at **1,500 rpm**. The frequency is 1,500 × 2 ÷ 60 = **50 Hz**, and the voltage is at its full grid value, even though the rotor turns only half as fast as the two-pole machine did.\n\nDrop to 750 rpm and the frequency falls to 25 Hz and the voltage to 50%. Raise it to 1,800 rpm and you get 60 Hz, the frequency used in the USA. Go all the way to 3,000 rpm and a four-pole machine would make 100 Hz at double voltage, which is far too fast for India's grid.\n\nThe lesson: frequency depends on how often a pole passes a coil, so doubling the poles halves the speed you need.",{"simplerExplanation":188,"hints":189},"Four poles means two waves per turn instead of one, so half the speed gives the same 50 Hz.",[190,191],"With four poles, there are two pole pairs. Frequency = rpm × 2 ÷ 60.","What rpm makes rpm × 2 ÷ 60 equal to 50?",{"id":193,"type":194,"title":195,"problem":196,"steps":197,"help":204},"we-hydro","worked_example","How many poles does a slow hydro generator need?","A hydro turbine turns at 150 rpm. How many poles must its generator have to supply India's 50 Hz grid?",[198,199,200,201,202,203],"Start from f = rpm × (poles ÷ 2) ÷ 60.","Put in the numbers: 50 = 150 × (poles ÷ 2) ÷ 60.","150 ÷ 60 = 2.5 turns per second, so 50 = 2.5 × (poles ÷ 2).","Pole pairs = 50 ÷ 2.5 = 20.","Poles = 20 × 2 = **40 poles**.","Check: 150 × 20 ÷ 60 = 3,000 ÷ 60 = 50 Hz. ✓",{"simplerExplanation":205},"The rotor turns 2.5 times a second. Each pair of poles gives one wave per turn. To get 50 waves a second you need 50 ÷ 2.5 = 20 pairs, which is 40 poles.",{"id":207,"type":68,"variant":208,"title":209,"markdown":210},"model-limit-generator","model_limit","What the lab leaves out","The lab is an ideal generator: voltage exactly proportional to speed, a perfect sine wave. Real power-station generators never change speed to change voltage. They are locked to the grid at exactly 3,000 rpm (or 1,500, or 150), and operators control the voltage by adjusting the current in the rotor's electromagnet instead. The speed-sweep in the lab is for seeing the physics, not how a station is run.",{"id":212,"type":50,"title":213,"eyebrow":214,"navLabel":215},"ch03","AC and DC: two ways for charge to move","Chapter 03","3 AC vs DC",{"id":217,"type":43,"markdown":218},"ac-dc-prose","**Direct current (DC)** pushes charge one way only. A torch cell, a phone battery and a car battery all give DC. Inside, a **chemical reaction** separates charge: one terminal ends up with a surplus of electrons, the other with a shortage, and the push is always from the same side. The symbol ⎓ on a charger means DC.\n\n**Alternating current (AC)** keeps reversing. The mains in your home swings smoothly from pushing one way, to zero, to pushing the other way, and back, 50 complete times every second. The symbol ~ means AC.\n\nSince each cycle contains two reversals, **50 Hz means the direction reverses 100 times a second**. The electrons in your fan's wire do not travel from the power station at all; they jiggle back and forth by a tiny fraction of a millimetre. The energy travels, carried by the electric and magnetic fields along the wires.",{"id":220,"type":221,"diagram":222,"caption":223,"alt":224},"diagram-ac-dc","diagram","ac-dc-waves","DC stays at one level on one side of zero. AC swings above and below zero, reversing direction twice in every cycle.","Two graphs of voltage against time. The top graph, labelled DC, is a flat horizontal line above the zero axis: the voltage stays constant and always in the same direction, like a battery. The bottom graph, labelled AC, is a smooth wave that rises above zero, falls through zero, dips the same distance below zero and rises again, repeating. One complete up-and-down wave is marked as one cycle; at 50 Hz there are 50 such cycles each second.",{"id":226,"type":227,"tone":228,"items":229},"spec-ac-dc","spec","blue",[230,234,238,242,246],{"label":231,"big":232,"value":233},"India mains","230 V ~","50 Hz AC from the socket; the direction reverses 100 times each second.",{"label":235,"big":236,"value":237},"USA mains","120 V ~","60 Hz AC; reverses 120 times each second. Japan uses both 50 and 60 Hz in different regions.",{"label":239,"big":240,"value":241},"Phone charger out","5 V ⎓","DC for USB charging; fast chargers negotiate higher DC voltages such as 9 V.",{"label":243,"big":244,"value":245},"AA cell","1.5 V ⎓","DC from a chemical reaction; no spinning, no frequency.",{"label":247,"big":248,"value":249},"Mains peak","≈ 325 V","230 V is an average-like value (RMS). The wave actually peaks at about 230 × 1.414 ≈ 325 V.",{"id":251,"type":43,"markdown":252,"help":253},"charger-prose","Your phone battery can only be charged with DC, at a low voltage. So the little brick you plug into the wall does two jobs: it **lowers the voltage** from 230 V to around 5 V, and it **rectifies** the current, turning the back-and-forth AC into one-way DC. Laptops, LED bulbs, TVs and inverter ACs all contain a circuit that does the same thing inside them. Most modern electronics quietly run on DC, made from AC at the last moment.\n\nSo why not simply send DC everywhere? Because, as the next chapters show, the grid depends on **transformers**, and transformers only work with AC. That single fact decided the shape of the world's electricity systems.",{"simplerExplanation":254,"anotherExample":255},"The wall gives AC at 230 V. The phone wants DC at about 5 V. The charger lowers the voltage and makes the current flow one way.","An inverter at home during a power cut does the reverse: it takes 12 V DC from a battery and turns it into 230 V AC so your fan and lights keep working.",{"id":257,"type":68,"variant":74,"title":258,"markdown":259},"nuance-charger","Modern chargers are cleverer than a plain transformer","Old chargers had a heavy iron transformer working at 50 Hz. Modern ones first turn mains into DC, then chop it on and off tens of thousands of times a second and feed that through a tiny, light transformer. Higher frequency lets the transformer shrink, which is why a 65 W laptop charger today can fit in your palm.",{"id":261,"type":68,"variant":262,"title":263,"markdown":264},"careful-ac-dc","careful","Low-voltage DC for experiments only","Batteries of 9 V or less are safe for home experiments with wires, bulbs and small motors. Mains AC at 230 V can kill. Never open a charger, plug or appliance, and never connect anything you have built to a wall socket.",{"id":266,"type":50,"title":267,"eyebrow":268,"navLabel":269},"ch04","Five ways to spin it (and one that doesn't)","Chapter 04","4 Power stations",{"id":271,"type":43,"markdown":272},"stations-prose","Every power station has to answer one question: **what will turn the turbine?** Coal, gas, uranium, falling water and moving air are simply different answers. After the turbine, the generator is almost the same in all of them. Choose a station below to follow its chain of energy, from source to socket.",{"id":274,"type":275,"title":276,"prompt":277,"options":278},"explorer-stations","explorer","Five ways to make electricity","Pick a station to see what turns its generator, or whether it has one at all.",[279,293,303,312,322],{"id":280,"label":281,"chain":282,"badge":289,"note":292},"coal-gas","Coal and gas",[283,284,285,286,287,288],"Chemical energy in fuel","Burn it in a boiler","Boil water to steam","Steam spins a turbine","Generator at 3,000 rpm","AC to the grid",{"text":290,"tone":291},"Spins a generator","yes","A coal station grinds coal to powder, burns it and uses the heat to boil water in kilometres of tubes. High-pressure steam blasts through a steam turbine, then is cooled back into water and reused. Gas stations often burn the gas in a jet-engine-like gas turbine first, then use the hot exhaust to make steam for a second turbine; this combined cycle is more efficient. Coal is India's largest source, with big stations in places such as Singrauli, Mundra and Talcher. Both release carbon dioxide.",{"id":294,"label":295,"chain":296,"badge":301,"note":302},"hydro","Hydro",[297,298,299,300,288],"Water held high behind a dam","Water falls down a pipe","Water spins a turbine","Many-pole generator",{"text":290,"tone":291},"A dam stores water high up, so it has gravitational potential energy. Let it fall through a pipe called a penstock and it spins a water turbine, which turns slowly, so the generator has many poles. Hydro can start up in minutes, which makes it very useful for meeting sudden jumps in demand. Pumped-storage hydro can even pump water back uphill when there is spare power, acting as a giant battery. Bhakra Nangal and Tehri are well-known Indian examples.",{"id":304,"label":305,"chain":306,"badge":310,"note":311},"nuclear","Nuclear",[307,308,285,286,309,288],"Uranium nuclei split","Heat in the reactor","Generator",{"text":290,"tone":291},"Splitting (fission of) uranium nuclei releases a huge amount of heat from a small amount of fuel. From there it is a kettle again: the heat makes steam, the steam spins a turbine. Some large nuclear sets use four-pole generators at 1,500 rpm. Nuclear stations produce very little carbon dioxide while running, but they must manage radioactive waste. India's stations include Tarapur, Rawatbhata and Kudankulam.",{"id":313,"label":314,"chain":315,"badge":320,"note":321},"wind","Wind",[316,317,318,309,319,288],"Moving air","Pushes the blades","Gearbox or direct drive","Electronics set 50 Hz",{"text":290,"tone":291},"Wind turbine blades turn slowly, often around 10–20 rpm. Some turbines use a gearbox to spin a fast generator; others use a wide, many-pole generator directly. Because the wind speed keeps changing, most modern turbines let the generator's frequency wander, then use power electronics to convert the output to a steady 50 Hz. Tamil Nadu and Gujarat have India's largest wind fleets.",{"id":323,"label":324,"chain":325,"badge":331,"note":334},"solar","Solar PV",[326,327,328,329,330,288],"Sunlight (photons)","Hit silicon cells","Electrons knocked free","DC from the panel","Inverter makes 50 Hz AC",{"text":332,"tone":333},"No spinning at all","no","A solar panel has no moving parts and no magnet. When light hits a silicon cell, it gives electrons enough energy to break free, and a built-in electric field in the cell pushes them one way. This is the **photovoltaic effect**, and it gives DC directly. An **inverter** then turns that DC into 50 Hz AC for the grid. Rooftop panels and huge parks such as Bhadla in Rajasthan all work this way. Solar output falls to zero every evening, just as demand peaks.",{"id":336,"type":68,"variant":69,"title":337,"markdown":338},"aha-kettle","Most power stations are giant kettles","Coal, gas (in its steam part), nuclear, and even most biomass and solar-thermal stations all do the same thing: **boil water to make steam that spins a turbine**. The fuel only decides how the water gets hot. And those huge cooling towers? The white clouds pouring from them are not smoke. They are **water vapour condensing into tiny droplets**, the same as the cloud from a kettle spout, from water used to cool the steam back into liquid.",{"id":340,"type":68,"variant":341,"title":342,"markdown":343},"misconception-towers","misconception","“The cooling tower is the chimney”","A thermal station's smoke comes out of a separate, tall, thin chimney (a stack), where flue gases carrying carbon dioxide and, unless cleaned, ash and sulphur are released. The fat, curved cooling towers release mostly clean water vapour. Nuclear stations have cooling towers or use sea water, but no chimney for combustion at all, because nothing is burned.",{"id":345,"type":194,"title":346,"problem":347,"steps":348},"we-efficiency","How much of the coal ends up as electricity?","A coal unit burns fuel releasing 1,500 MW of heat and sends 500 MW of electricity to the grid. What is its efficiency, and where does the rest go?",[349,350,351,352],"Efficiency = useful output ÷ input = 500 MW ÷ 1,500 MW.","500 ÷ 1,500 = 1\u002F3 ≈ 0.33, so the efficiency is about **33%**.","The other 1,500 − 500 = **1,000 MW** leaves as heat, mostly carried away by the cooling water (the plume from the cooling towers) and in hot flue gas.","So for every unit of electricity, roughly two units' worth of heat is released to the surroundings. This is typical for older steam stations; modern combined-cycle gas plants reach around 55–60%.",{"id":354,"type":50,"title":355,"eyebrow":356,"navLabel":357},"ch05","The journey to your socket","Chapter 05","5 The journey",{"id":359,"type":43,"markdown":360},"journey-intro","Electricity leaves a generator at a moderate voltage, is pushed up to hundreds of thousands of volts for the long trip, and is stepped down in stages as it gets closer to you. Every change of voltage happens in a **transformer**. Here is the typical Indian route.",{"id":362,"type":363,"title":364,"items":365},"steps-journey","steps","From turbine hall to wall socket",[366,369,373,377,381,385,389,393,397],{"title":309,"tag":367,"text":368},"11–25 kV","The stator coils deliver three-phase AC at about 11–25 kV, depending on the size of the unit.",{"title":370,"tag":371,"text":372},"Step-up transformer","→ 220 \u002F 400 \u002F 765 kV","At the station's switchyard, a generator transformer raises the voltage enormously, so the current becomes small.",{"title":374,"tag":375,"text":376},"Transmission lines","tall steel towers","Long-distance lines, up to 765 kV in India, carry bulk power hundreds of kilometres between regions.",{"title":378,"tag":379,"text":380},"Grid substation","→ 132 \u002F 33 kV","Near a city, transformers step the voltage down to 132 kV or 33 kV for sub-transmission across the district.",{"title":382,"tag":383,"text":384},"Distribution substation","→ 11 kV","Local substations step down again to 11 kV, carried along roads on poles or in underground cables.",{"title":386,"tag":387,"text":388},"Street transformer","→ 415 V \u002F 230 V","The grey transformer on a pole or plinth steps 11 kV down to about 400–415 V between phases, or 230 V between one phase and neutral.",{"title":390,"tag":391,"text":392},"Service line and meter","your connection","Most homes get one phase at 230 V; bigger homes may take all three. The energy meter records every kWh.",{"title":394,"tag":395,"text":396},"Distribution board and MCB","protection","Inside the home, miniature circuit breakers (MCBs) switch off a circuit if it draws too much current.",{"title":398,"tag":399,"text":400},"Socket","230 V, 50 Hz","Finally, 230 V AC at 50 Hz reaches the socket, and your fan, geyser or phone charger.",{"id":402,"type":403,"title":404,"note":405,"scale":406,"rungs":407},"ladder-voltages","ladder","The voltage ladder: from a torch cell to a 765 kV line","Log scale: each step up the chart is ten times bigger. The highest line voltage is about 500,000 times an AA cell.","log",[408,411,415,419,423,427,431,435,439,443,447],{"label":243,"value":409,"display":410},1.5,"1.5 V",{"label":412,"value":413,"display":414},"USB phone charging",5,"5 V",{"label":416,"value":417,"display":418},"Home socket (India)",230,"230 V",{"label":420,"value":421,"display":422},"Between phases, street supply",415,"≈ 415 V",{"label":424,"value":425,"display":426},"Local distribution",11000,"11 kV",{"label":428,"value":429,"display":430},"Railway overhead wire",25000,"25 kV",{"label":432,"value":433,"display":434},"Sub-transmission",33000,"33 kV",{"label":436,"value":437,"display":438},"Regional lines",132000,"132 kV",{"label":440,"value":441,"display":442},"State transmission",220000,"220 kV",{"label":444,"value":445,"display":446},"Inter-state transmission",400000,"400 kV",{"label":448,"value":449,"display":450},"Highest AC lines in India",765000,"765 kV",{"id":452,"type":68,"variant":74,"title":453,"markdown":454},"three-phase-nuance","Why three wires on the poles?","Power stations make **three-phase** AC: three separate waves, each a third of a cycle behind the next, from three sets of stator coils. Three phases carry power more smoothly and with less copper than one. Your home usually takes one phase plus a neutral (230 V). Between any two phases the voltage is about 230 × 1.73 ≈ 400 V, which is why workshops and big pumps use three-phase supplies.",{"id":456,"type":68,"variant":262,"title":457,"markdown":458},"careful-lines","Stay far away from lines and substations","High-voltage electricity can jump through the air to a kite string, a metal pole or a person who comes too close, without any touch at all. Never fly kites near power lines, never climb towers or transformer fences, and stay away from any fallen wire. Tell an adult and the electricity board.",{"id":460,"type":50,"title":461,"eyebrow":462,"navLabel":463},"ch06","Why transmit at such high voltage?","Chapter 06","6 Why high voltage",{"id":465,"type":43,"markdown":466,"help":467},"why-hv-prose","Transmission wires are thick aluminium, but over hundreds of kilometres even they have some resistance, a few ohms. Current flowing through resistance heats the wire, and that heat is energy lost.\n\nTwo formulas explain everything:\n\n- The power delivered is **P = V × I**. For a fixed amount of power, you can use a high voltage with a small current, or a low voltage with a large current.\n- The power wasted as heat in the wire is **loss = I² × R**. It depends on the **square** of the current.\n\nSo raise the voltage 10 times and, for the same power, the current falls to one-tenth. The loss falls to (1\u002F10)² = **one-hundredth**. That square is the whole reason for tall towers and enormous voltages.",{"simplerExplanation":468,"anotherExample":469,"hints":470},"The wire wastes energy according to how much current flows through it, and doubling the current makes four times the waste. High voltage lets you send the same power with a small current, so very little is wasted.","Think of delivering the same amount of water through a long, slightly leaky hose. Send it as a thin, high-pressure jet and the flow is small, so little leaks. Send it as a gushing, low-pressure flow and much more is lost on the way.",[471,472],"Same power: if V goes up n times, I goes down n times.","Loss depends on I squared, so it goes down n × n times.",{"id":474,"type":124,"items":475},"formulas-transmission",[476,479,482,485],{"expression":477,"caption":478},"P = V × I","Power in watts = voltage in volts × current in amps.",{"expression":480,"caption":481},"I = P ÷ V","For a fixed power, current is smaller when voltage is higher.",{"expression":483,"caption":484},"P_loss = I² × R","Heat lost in a wire of resistance R carrying current I.",{"expression":486,"caption":487},"V × n → I ÷ n → loss ÷ n²","Raise the voltage n times for the same power and the line loss falls n² times.",{"id":489,"type":140,"prompt":490,"options":491,"explanation":500},"predict-loss","A line delivers the same power, but its voltage is raised from 25 kV to 400 kV (16 times higher). What happens to the energy lost as heat in the line?",[492,494,496,498],{"id":144,"label":493},"It falls to 1\u002F16 of what it was",{"id":147,"label":495},"It falls to 1\u002F256 of what it was",{"id":150,"label":497},"It rises 16 times, because the voltage is higher",{"id":153,"label":499},"It stays the same, because the power is the same","**1\u002F256.** Same power at 16 times the voltage means one-sixteenth of the current. Loss depends on current squared, so it falls by 16 × 16 = 256 times. The worked example below puts real numbers on this.",{"id":502,"type":194,"title":503,"problem":504,"steps":505,"help":511},"we-transmission","Sending 10 MW down a 10 Ω line","A station must send 10 MW (10,000,000 W) along a line with a total resistance of 10 Ω. Compare the loss at 25 kV and at 400 kV.",[506,507,508,509,510],"**At 25 kV:** I = P ÷ V = 10,000,000 ÷ 25,000 = **400 A**.","Loss = I² × R = 400 × 400 × 10 = 1,600,000 W = **1.6 MW**. That is 16% of the power, gone as heat.","**At 400 kV:** I = 10,000,000 ÷ 400,000 = **25 A**.","Loss = 25 × 25 × 10 = 6,250 W ≈ **6.3 kW**. That is about 0.06% of the power.","Compare: the voltage went up 400,000 ÷ 25,000 = 16 times; the current went down 16 times; the loss went down 1,600,000 ÷ 6,250 = **256 = 16²** times. ✓",{"simplerExplanation":512,"hints":513},"At low voltage, 400 A heats the wire and wastes a sixth of the power. At high voltage, only 25 A flows and the waste is tiny.",[514,515],"Always find the current first with I = P ÷ V.","Then square the current and multiply by R.",{"id":517,"type":518,"itemId":519,"prompt":520,"check":521,"hints":525,"feedback":528},"practice-loss","practice","electricity.deepen-line-loss","A line carries 50 A through a total resistance of 8 Ω. How much power, in watts, is lost as heat in the line?",{"kind":522,"answer":523,"tolerance":5,"unit":524},"number",20000,"W",[526,527],"Use loss = I² × R.","50 × 50 = 2,500. Now multiply by 8.",{"correct":529,"incorrect":530},"Right: 50² × 8 = 2,500 × 8 = 20,000 W, or 20 kW.","Square the current first: 50 × 50 = 2,500. Then 2,500 × 8 = 20,000 W.",{"id":532,"type":68,"variant":341,"title":533,"markdown":534},"misconception-hv","“Higher voltage must mean more loss”","It feels as if a bigger push should waste more, but the loss in a wire is set by the **current** through it, not by the voltage of the line above the ground. The voltage that matters for heating the wire is only the small drop along the wire itself, which is I × R. Raise the line voltage, and for the same power the current, and so that small drop, both get smaller.",{"id":536,"type":68,"variant":208,"title":537,"markdown":538},"nuance-real-losses","Real grids still lose some energy","Our example uses a single made-up resistance. Real networks lose energy in every transformer and in the many kilometres of low-voltage wiring near homes, where currents are large again. Theft and faulty meters add ‘commercial’ losses. India's aggregate technical and commercial (AT&C) losses at the national level came down from 21.91% in 2020-21 to 16.16% in 2024-25, much of it lost in the last few kilometres rather than on the big towers. Individual states differ a lot, and the national scheme's target is 12–15%.",{"id":540,"type":50,"title":541,"eyebrow":542,"navLabel":543},"ch07","Transformers: the grid's gearboxes","Chapter 07","7 Transformers",{"id":545,"type":43,"markdown":546,"help":547},"transformer-prose","A transformer is Faraday's iron ring, grown up. Two coils are wound on the same iron core, with no electrical connection between them.\n\n1. AC flows in the **primary** coil. Because the current keeps changing, it makes a magnetic field that keeps changing.\n2. The iron core carries that changing field through the **secondary** coil.\n3. A changing field through a coil induces a voltage (Faraday again), so AC appears in the secondary.\n\nEvery turn of wire, on either coil, gets the same voltage per turn. So the coil with more turns has the bigger voltage:\n\n**Vs ÷ Vp = Ns ÷ Np**\n\nMore turns on the secondary means a **step-up** transformer; fewer means **step-down**.",{"simplerExplanation":548,"anotherExample":549,"hints":550},"The voltage is shared out per turn of wire. If the secondary has half as many turns, it gets half the voltage.","A gearbox on a bicycle trades speed for force. A transformer trades voltage for current: step the voltage up 10 times and the current steps down 10 times.",[551,552],"Write it as a ratio: output voltage ÷ input voltage = output turns ÷ input turns.","Power in ≈ power out, so if voltage goes up, current goes down.",{"id":554,"type":221,"diagram":555,"caption":556,"alt":557},"diagram-transformer","transformer","Two coils on one iron core. The changing field from the primary induces a voltage in the secondary; the turns ratio sets the voltage ratio.","A square iron core shaped like a picture frame. On the left side a primary coil with many turns is connected to an AC supply. On the right side a secondary coil with fewer turns is connected to a load. Arrows around the core show the changing magnetic field passing from the primary coil to the secondary coil through the iron. Labels show primary voltage Vp and turns Np on the left, and secondary voltage Vs and turns Ns on the right, with the rule Vs divided by Vp equals Ns divided by Np.",{"id":559,"type":124,"items":560},"formulas-transformer",[561,564,567],{"expression":562,"caption":563},"Vs ÷ Vp = Ns ÷ Np","The voltage ratio equals the turns ratio.",{"expression":565,"caption":566},"Vp × Ip ≈ Vs × Is","Ideal transformer: power in equals power out. Real ones are about 97–99% efficient.",{"expression":568,"caption":569},"Is ÷ Ip = Np ÷ Ns","Current changes the opposite way to voltage.",{"id":571,"type":194,"title":572,"problem":573,"steps":574},"we-transformer","A 230 V to 12 V transformer","A transformer has 1,150 turns on its primary, which is connected to 230 V AC. Its secondary has 60 turns. Find the output voltage, and the primary current when the secondary supplies 2 A to a lamp. Assume it is ideal.",[575,576,577,578,579],"Vs ÷ Vp = Ns ÷ Np, so Vs = Vp × Ns ÷ Np.","Vs = 230 × 60 ÷ 1,150 = 13,800 ÷ 1,150 = **12 V**.","Power out = Vs × Is = 12 × 2 = **24 W**.","Ideal transformer: power in = power out = 24 W.","Primary current Ip = 24 ÷ 230 ≈ **0.10 A**. Voltage stepped down about 19 times; current stepped up about 19 times.",{"id":581,"type":518,"itemId":582,"prompt":583,"check":584,"hints":587,"feedback":590},"practice-turns","electricity.deepen-turns-ratio","A station's step-up transformer takes 25 kV from the generator and must deliver 400 kV to the line. What is the ratio Ns ÷ Np of secondary turns to primary turns?",{"kind":522,"answer":585,"tolerance":586},16,0.01,[588,589],"Ns ÷ Np = Vs ÷ Vp.","400 ÷ 25 = ?",{"correct":591,"incorrect":592},"Yes: 400 kV ÷ 25 kV = 16, so the secondary has 16 times as many turns as the primary.","The turns ratio equals the voltage ratio: 400 ÷ 25 = 16.",{"id":594,"type":68,"variant":69,"title":595,"markdown":596},"aha-transformer-ac","Why transformers need AC","Connect a transformer to a steady DC battery and the secondary gives a brief kick when you connect it, then nothing, exactly as Faraday saw in 1831. Steady current makes a steady field, and a steady field induces no voltage. AC changes all the time, so it induces a voltage all the time. This is why the world's grids chose AC: it could be stepped up and down cheaply with no moving parts.",{"id":598,"type":68,"variant":74,"title":599,"markdown":600},"nuance-hvdc","DC is making a comeback, for long links","With modern power electronics, very long lines can be run as high-voltage DC (HVDC), with converter stations at each end turning AC into DC and back. HVDC avoids some AC losses over very long distances and can link grids that are not in step. India has several, including the ±800 kV, 6,000 MW NER–Agra link, which carries power 1,728 km from Biswanath Chariali in Assam to Agra. Houses, though, still get AC.",{"id":602,"type":50,"title":603,"eyebrow":604,"navLabel":605},"ch08","Power and energy: what the meter counts","Chapter 08","8 Power and energy",{"id":607,"type":43,"markdown":608,"help":609},"power-energy-prose","**Power** is how fast energy is transferred, measured in watts (W). One watt is one joule every second. For an appliance on the mains, **P = V × I**. A 1,500 W kettle on 230 V draws about 1,500 ÷ 230 ≈ 6.5 A.\n\n**Energy** is power multiplied by time: **E = P × t**. Energy in joules is a very small unit for a household, so electricity companies use a bigger one: the **kilowatt-hour (kWh)**, the energy used by 1,000 W running for one hour. On an Indian bill, one kWh is simply called **one unit**. One kWh equals 1,000 W × 3,600 s = 3,600,000 J, or 3.6 MJ.\n\nA quick way to find units: **watts × hours ÷ 1,000**. The extend layer turns this into a full bill with real appliances and tariffs.",{"simplerExplanation":610,"anotherExample":611},"Watts tell you how hungry something is right now. Units (kWh) tell you how much it ate in total. A hungry thing used briefly can eat less than a small thing left on all day.","A 10 W LED bulb left on for 100 hours uses 10 × 100 ÷ 1,000 = 1 unit, the same as a 2,000 W geyser in 30 minutes.",{"id":613,"type":124,"items":614},"formulas-energy",[615,617,620,623],{"expression":477,"caption":616},"Power in watts from voltage and current.",{"expression":618,"caption":619},"E = P × t","Energy = power × time. Watts × seconds gives joules; kilowatts × hours gives kWh.",{"expression":621,"caption":622},"units = W × h ÷ 1000","One unit on an Indian bill is 1 kWh.",{"expression":624,"caption":625},"1 kWh = 3.6 MJ","1,000 W × 3,600 s = 3,600,000 J.",{"id":627,"type":194,"title":628,"problem":629,"steps":630},"we-geyser","A morning's hot water","A 2,000 W geyser runs for 30 minutes each morning on 230 V. Find the current it draws, the energy it uses each day in kWh, and the cost for 30 days at ₹7 per unit.",[631,632,633,634,635],"Current: I = P ÷ V = 2,000 ÷ 230 ≈ **8.7 A**.","Power in kW: 2,000 W = 2 kW. Time: 30 minutes = 0.5 h.","Energy per day: E = 2 × 0.5 = **1 kWh**, which is 1 unit.","For 30 days: 1 × 30 = 30 units.","Cost: 30 × ₹7 = **₹210** a month. (Tariffs vary by state and by slab; ₹7 is only an example.)",{"id":637,"type":518,"itemId":638,"prompt":639,"check":640,"hints":643,"feedback":646},"practice-kettle","electricity.deepen-kettle-units","A 1,500 W electric kettle is used for a total of 20 minutes a day. How many units (kWh) does it use in a day?",{"kind":522,"answer":641,"tolerance":586,"unit":642},0.5,"kWh",[644,645],"20 minutes is 20 ÷ 60 = 1\u002F3 of an hour.","units = 1,500 × (1\u002F3) ÷ 1,000.",{"correct":647,"incorrect":648},"Right: 1.5 kW × 1\u002F3 h = 0.5 kWh, half a unit.","Change to kW and hours first: 1.5 kW × (20 ÷ 60) h = 1.5 × 0.333 = 0.5 kWh.",{"id":650,"type":68,"variant":341,"title":651,"markdown":652},"misconception-power-energy","“A kWh is a kilowatt per hour”","It is a kilowatt **times** an hour, not per hour. Kilowatts measure a rate (how fast energy is used); kilowatt-hours measure an amount (how much energy in total). Your meter counts kWh, just as a water meter counts litres, not litres per second.",{"id":654,"type":50,"title":655,"eyebrow":656,"navLabel":657},"ch09","Balancing the grid, second by second","Chapter 09","9 Balancing the grid",{"id":659,"type":43,"markdown":660,"help":661},"balance-prose","All the big generators across mainland India are connected to one grid, and they all spin **in step**, like dancers following the same beat. That beat is the grid frequency, 50 Hz.\n\nNow picture the evening. Millions of people get home, switch on lights, fans, TVs and, in summer, air conditioners. Demand jumps. For a moment the generators are asked for more power than their turbines are supplying. Where does the extra come from? From the **spinning energy** of the rotors themselves. They slow down, very slightly, and the frequency dips, say from 50.00 to 49.95 Hz.\n\nThe opposite happens on a sunny, quiet Sunday afternoon: lots of solar, low demand, too much supply. The rotors speed up a touch and the frequency creeps above 50 Hz.\n\nSo **frequency is the grid's pulse**. Control rooms in every region watch it constantly and order stations to raise or lower output, keeping supply and demand matched every second.",{"simplerExplanation":662,"anotherExample":663},"If people use more than the stations are making, the generators slow down a little and the frequency drops. If stations make more than is being used, the generators speed up. Operators watch the frequency to know which way to adjust.","It is like cycling up a slope while keeping a steady speed. When the road gets steeper (more demand), you must push harder at once, or you slow down.",{"id":665,"type":227,"tone":666,"items":667},"spec-grid","amber",[668,672,676,680],{"label":669,"big":670,"value":671},"Reference frequency","50.00 Hz","The target for India's national grid.",{"label":673,"big":674,"value":675},"Allowed band","49.90–50.05 Hz","The allowable band in Regulation 30(1) of the Indian Electricity Grid Code 2023; operators must bring frequency back inside it quickly.",{"label":677,"big":678,"value":679},"Too low","below band","Demand exceeds supply: raise generation fast, and in emergencies automatically disconnect some load.",{"label":681,"big":682,"value":683},"Too high","above band","Supply exceeds demand: cut generation, store energy (pumped hydro, batteries) or reduce solar and wind output.",{"id":685,"type":43,"markdown":686},"balance-tools","Operators have a toolbox for keeping the balance:\n\n- **Forecasting.** Demand follows patterns: it rises in the morning, peaks in the evening, and is higher in the heat of May than in December. Weather forecasts predict solar and wind output.\n- **Fast responders.** Hydro and gas stations can change output within minutes. Many large thermal units are also required to respond automatically to small frequency changes.\n- **Storage.** Pumped-storage hydro and, increasingly, large battery banks soak up surplus solar in the afternoon and give it back in the evening.\n- **Last resort.** If frequency falls dangerously, automatic relays switch off some areas (load shedding) to save the rest of the grid from collapsing.\n\nThe hardest hour is the **evening peak**. Solar output fades just as homes light up, so other stations must ramp up quickly while the sun sets.",{"id":688,"type":68,"variant":689,"title":690,"markdown":691},"careful-blackout","example","When the balance fails","On 30 and 31 July 2012, heavy demand and overloaded lines tripped large parts of India's grid. The second day left around 620 million people, about half the country, without power for hours — the largest blackout ever recorded by the number of people affected. Today's tighter frequency band, stronger inter-regional lines and faster control all came partly from lessons learned then.",{"id":693,"type":694,"prompt":695},"reflect-balance","reflection","Solar panels produce most at midday, but many homes use most electricity in the evening. Suggest two different ways a grid could deal with this mismatch, and one drawback of each.",{"id":697,"type":50,"title":698,"eyebrow":699,"navLabel":700},"ch10","India's generation mix","Chapter 10","10 India's mix",{"id":702,"type":43,"markdown":703},"mix-prose","Where does India's electricity actually come from? The answer changes year by year, as solar farms spread across Rajasthan and Gujarat and wind grows in the south. The table shows **approximate, rounded shares of electricity generated** (energy produced, not capacity) over roughly the 12 months up to mid-2026, from published data compilations. Exact figures differ between sources and years, so treat these as a picture of the balance, not precise numbers.",{"id":705,"type":706,"caption":707,"columns":708,"rows":713},"table-mix","table","India's electricity generation by source, approximate shares, about mid-2025 to mid-2026 (rounded; source: Low-Carbon Power compilation of national data)",[709,710,711,712],"Source","Share of generation","How it makes electricity","Notes",[714,719,723,727,731,734,739],[715,716,717,718],"Coal (and lignite)","about 68%","Steam turbine + generator","Still the backbone; runs day and night",[324,720,721,722],"about 9–10%","Photovoltaic cells, no spinning","Fastest growing; zero output at night",[295,724,725,726],"about 9%","Water turbine + many-pole generator","Varies with monsoon rain; quick to ramp",[314,728,729,730],"about 6%","Wind turbine + generator","Strongest in the south-west monsoon months",[305,732,717,733],"about 2.6%","Steady, low-carbon output",[735,736,737,738],"Gas","about 2%","Gas and steam turbines","Often used for peaks; gas is costly",[740,736,741,742],"Bioenergy and others","Mostly steam turbines","Bagasse from sugar mills, biomass",{"id":744,"type":68,"variant":74,"title":745,"markdown":746},"nuance-capacity","Capacity is not the same as generation","Capacity is how much a station **could** produce at full power; generation is how much it **actually** produces over a year. By mid-2025 India had reached half of its installed capacity from non-fossil sources (solar, wind, hydro, nuclear), yet coal still generated about two-thirds of the electricity. Why? A solar panel only works in daylight and produces far below its rating on average, while a coal unit can run most hours of the year. Solar's share of generation is therefore much smaller than its share of capacity.",{"id":748,"type":50,"title":749,"eyebrow":750,"navLabel":751},"ch11","Check yourself","Chapter 11","11 Quiz and summary",{"id":753,"type":754,"title":9,"questions":755},"quiz-deepen","quiz",[756,769,782,795,808,821,834,847,860,873],{"itemId":757,"prompt":758,"options":759,"correct":147,"why":768},"electricity.deepen-q-induction","A strong magnet sits perfectly still inside a coil connected to a meter. What does the meter show?",[760,762,764,766],{"id":144,"label":761},"A large steady current",{"id":147,"label":763},"Zero: the field is not changing",{"id":150,"label":765},"An alternating current at 50 Hz",{"id":153,"label":767},"A small current that slowly grows","Induction needs a **changing** magnetic field through the coil. A still magnet gives a steady field, so no voltage is induced.",{"itemId":770,"prompt":771,"options":772,"correct":147,"why":781},"electricity.deepen-q-frequency","A two-pole generator spins at 3,600 rpm. What frequency does it produce?",[773,775,777,779],{"id":144,"label":774},"50 Hz",{"id":147,"label":776},"60 Hz",{"id":150,"label":778},"120 Hz",{"id":153,"label":780},"3,600 Hz","f = 3,600 × 1 ÷ 60 = 60 Hz, the grid frequency used in the USA.",{"itemId":783,"prompt":784,"options":785,"correct":144,"why":794},"electricity.deepen-q-four-pole","Why can a four-pole generator run at 1,500 rpm and still supply a 50 Hz grid?",[786,788,790,792],{"id":144,"label":787},"Each turn sends two complete waves past each coil",{"id":147,"label":789},"Four poles make the voltage twice as high",{"id":150,"label":791},"The transformer doubles the frequency",{"id":153,"label":793},"It cannot; it would make 25 Hz","Four poles means two pole pairs, so two cycles per turn: 1,500 × 2 ÷ 60 = 50 Hz.",{"itemId":796,"prompt":797,"options":798,"correct":150,"why":807},"electricity.deepen-q-reversals","How many times each second does the current direction reverse on India's 50 Hz mains?",[799,801,803,805],{"id":144,"label":800},"25",{"id":147,"label":802},"50",{"id":150,"label":804},"100",{"id":153,"label":806},"230","Each cycle has two reversals (one way to the other, and back). 50 cycles × 2 = 100 reversals a second.",{"itemId":809,"prompt":810,"options":811,"correct":153,"why":820},"electricity.deepen-q-solar","Which of these makes electricity without spinning a generator?",[812,814,816,818],{"id":144,"label":813},"A nuclear station",{"id":147,"label":815},"A hydro dam",{"id":150,"label":817},"A wind turbine",{"id":153,"label":819},"A solar PV panel","Solar cells use the photovoltaic effect: light frees electrons in silicon and gives DC directly, with no magnet or moving part.",{"itemId":822,"prompt":823,"options":824,"correct":150,"why":833},"electricity.deepen-q-cooling-tower","What is the white plume rising from a power station's cooling tower mostly made of?",[825,827,829,831],{"id":144,"label":826},"Smoke from burning coal",{"id":147,"label":828},"Carbon dioxide",{"id":150,"label":830},"Water vapour condensing into droplets",{"id":153,"label":832},"Radioactive gas","Cooling towers release heat by evaporating some cooling water. The visible cloud is tiny water droplets, like steam from a kettle.",{"itemId":835,"prompt":836,"options":837,"correct":147,"why":846},"electricity.deepen-q-hv-loss","The same power is sent at 5 times the voltage. By what factor does the heat loss in the line change?",[838,840,842,844],{"id":144,"label":839},"It falls 5 times",{"id":147,"label":841},"It falls 25 times",{"id":150,"label":843},"It rises 5 times",{"id":153,"label":845},"It does not change","Current falls 5 times (I = P ÷ V). Loss = I²R, so it falls 5² = 25 times.",{"itemId":848,"prompt":849,"options":850,"correct":144,"why":859},"electricity.deepen-q-transformer","A transformer has 4,000 turns on its primary and 200 on its secondary. The primary is on 11,000 V. What is the secondary voltage (ideal)?",[851,853,855,857],{"id":144,"label":852},"550 V",{"id":147,"label":854},"2,200 V",{"id":150,"label":856},"220,000 V",{"id":153,"label":858},"55 V","Vs = Vp × Ns ÷ Np = 11,000 × 200 ÷ 4,000 = 11,000 ÷ 20 = 550 V.",{"itemId":861,"prompt":862,"options":863,"correct":147,"why":872},"electricity.deepen-q-transformer-dc","Why would a transformer connected to a steady 12 V battery give no steady output?",[864,866,868,870],{"id":144,"label":865},"Batteries are too weak for transformers",{"id":147,"label":867},"Steady current makes a steady field, which induces no voltage",{"id":150,"label":869},"The iron core blocks DC",{"id":153,"label":871},"It would, but only at 50 Hz","Induction needs change. DC gives a constant field after the first instant, so the secondary gets nothing after a brief kick.",{"itemId":874,"prompt":875,"options":876,"correct":147,"why":885},"electricity.deepen-q-frequency-dip","On a hot evening, demand suddenly rises faster than stations can increase output. What happens first to the grid frequency?",[877,879,881,883],{"id":144,"label":878},"It rises above 50 Hz",{"id":147,"label":880},"It dips slightly below 50 Hz",{"id":150,"label":882},"It stays exactly at 50 Hz",{"id":153,"label":884},"It drops to zero","The extra energy is drawn from the spinning rotors, which slow slightly, so the frequency dips. Operators then raise generation to bring it back.",{"id":887,"type":888,"title":889,"points":890},"cheat-sheet","summary","Cheat sheet",[891,892,893,894,895,896,897,898,899,900,901,902],"**Induction (Faraday, 1831):** a *changing* magnetic field through a coil induces a voltage. Faster change and more turns give a bigger push; a still magnet gives nothing.","**Generator:** a spinning electromagnet (rotor) inside copper coils (stator) makes AC. f = rpm × (poles ÷ 2) ÷ 60.","**50 Hz:** 3,000 rpm with 2 poles, or 1,500 rpm with 4 poles. The USA uses 60 Hz (3,600 rpm, 2 poles). Voltage and frequency both rise with speed.","**AC vs DC:** batteries give DC by chemistry; generators give AC. At 50 Hz the direction reverses 100 times a second. Chargers turn 230 V AC into about 5 V DC.","**Power stations:** coal, gas and nuclear boil water to spin turbines; hydro uses falling water; wind uses moving air; solar PV has no spinning parts at all.","**Cooling-tower plumes** are condensing water vapour, not smoke.","**Journey:** generator 11–25 kV → step-up to 220\u002F400\u002F765 kV → transmission → 132\u002F33 kV → 11 kV → street transformer 415 V (three-phase) \u002F 230 V → meter → MCB → socket.","**Why high voltage:** P = V × I and loss = I²R. Same power at n times the voltage means 1\u002Fn the current and 1\u002Fn² the loss.","**Transformers:** Vs ÷ Vp = Ns ÷ Np; ideal power in = power out; they only work with AC.","**Energy:** E = P × t. 1 unit = 1 kWh = 3.6 MJ. Units = watts × hours ÷ 1,000.","**Grid balance:** frequency dips when demand exceeds supply and rises when supply exceeds demand. India's normal band is 49.90–50.05 Hz.","**India's mix (approx., 2025–26):** coal about two-thirds of generation; solar and hydro about 9% each; wind about 6%; nuclear about 2.6%.",{"id":904,"type":905,"sourceIds":906},"sources-deepen","sources",[907,908,909,910,911,912,913,914,915,916,917],"elec-deepen-eia-generation","elec-deepen-eia-delivery","elec-deepen-hyperphysics-faraday","elec-deepen-hyperphysics-transformer","elec-deepen-wiki-faraday","elec-deepen-wiki-india-grid","elec-deepen-mercom-frequency","elec-deepen-lowcarbon-india","elec-deepen-pib-atc-losses","elec-deepen-wiki-blackout-2012","elec-deepen-cerc-iegc-2023",[907,908,909,910,911,912,913,914,915,916,917],"needs_review",{"generatedBy":921,"notes":922},"claude-code","Draft generated locally; pending owner review.","12c998a653198a989d932c478851bdebecce4de4ed00d72a0bce422ca332942b",{"component:generator@1":925,"diagram:ac-dc-waves":926,"logic:practice":927,"diagram:transformer":928,"source:elec-deepen-cerc-iegc-2023":929,"source:elec-deepen-eia-delivery":930,"source:elec-deepen-eia-generation":931,"source:elec-deepen-hyperphysics-faraday":932,"source:elec-deepen-hyperphysics-transformer":933,"source:elec-deepen-lowcarbon-india":934,"source:elec-deepen-mercom-frequency":935,"source:elec-deepen-pib-atc-losses":936,"source:elec-deepen-wiki-blackout-2012":937,"source:elec-deepen-wiki-faraday":938,"source:elec-deepen-wiki-india-grid":939},"828c8bbf0f75223cd6883291c4085a419c3b9c99888596a1a4ee5f7a51aac2f2","f44677a81e3cf0d5be75c8c3a956c038d3e8b174c2bf253c3c6109679a987ba6","3d6b0fe1b15255975a32b0fcd94e8019bc959ad45cbf12e136e86149549c6878","81f12770d6824f5fadd4b8b22a74750af19dd80301c24f366a695f2bc1182aec","c7093aab4824fcf1656498c1ad47d619e9dbe148f3357ca09f4d69efc1b5f297","9722eab710673bafcf9a71b51612514434ae2ac87f88a2c23b56ba9b021d1911","f098268d0fde517e2d61fbfd5aefce8c158a110dc35cdd87a5419e3f5b5a2a8f","f614623ba6661a39f4325a051a4cce61582540fc19086fc129de6f5b098fe729","dd7bbf2e8fb2508f8f5bac3c5e697ed5c402d1d97fc775a250f1b1cc43f5a54c","f3d288e906da20b146aca9f8599721bd18e3a2f582fc58968b50188b02ec053a","cb5909f0026a57a80c757aae480040a5454c94bf6b22746f1c9a28af01d53d63","f058a4a842c7116a2bcac24dd62a6fde70d3429207336a92769b3c1bb64d0b7c","459222da060c6005236fc88d2acb8362511ffbdf72e720074c75eac1c5cc6769","0bb50b4769596e41bb01c7766237f4ae104f80142291f789ed25c2f6dfd526c8","481c36a8f937e1afa17d02f6ae5d1a1c453dce95639945baccaa25936c16c8af",{"state":941,"reviewer":942,"selfReview":943,"reviewedAt":944,"method":945},"approved","The library owner",true,"2026-09-20T10:18:37.581Z","owner_bulk","preview-7e1cbbcc4f",1789899599752]