[{"data":1,"prerenderedAt":1040},["ShallowReactive",2],{"layer:electricity:extend":3},{"layer":4,"contentHash":1021,"dependencyHashes":1022,"approval":1034,"releaseId":1039},{"schemaVersion":5,"conceptId":6,"locale":7,"depth":8,"revision":5,"title":9,"subtitle":10,"summary":11,"objectives":12,"estimatedMinutes":18,"plate":19,"blocks":43,"sourceIds":1016,"reviewStatus":1017,"authoring":1018},1,"electricity","en","extend","Power, bills, safety and the future","From watts on a rating plate to units on your bill, the milliamps that matter, and the grid that is coming","Use P = V × I and E = P × t to read rating plates and work out a real electricity bill in units (kWh). Learn why current through the body is what injures, how earth pins, MCBs and RCCBs protect you, what to do in a shock emergency, and how solar, storage and smart meters are changing the grid.",[13,14,15,16,17],"Calculate power from voltage and current, and energy in kWh (units) from power and time, then turn units into rupees.","Read a full appliance rating plate and a BEE star label, and estimate what standby power costs over a year.","Explain with numbers why wet skin makes mains electricity so much more dangerous, and how earthing, MCBs and RCCBs each protect you.","Know exactly what to do, and what never to do, if someone is receiving an electric shock.","Estimate a simplified rooftop-solar payback and explain why the evening peak, storage and time-of-day tariffs matter.",40,{"title":20,"rows":21},"Rating plate",[22,25,28,31,34,37,40],{"label":23,"value":24},"Depth","Extend: projects and wider contexts",{"label":26,"value":27},"Reading time","About 40 minutes",{"label":29,"value":30},"Prior knowledge","Voltage, current, resistance, V = I × R",{"label":32,"value":33},"Chapters","11",{"label":35,"value":36},"Labs","Energy bill, current through the body",{"label":38,"value":39},"Units used","W, kW, kWh (units), ₹, V, A, mA, Ω",{"label":41,"value":42},"Safety","No mains experiments. Batteries ≤ 9 V only.",[44,48,51,57,63,72,88,139,154,159,164,170,199,209,218,233,249,254,259,262,303,308,322,327,332,335,353,400,404,414,419,422,432,438,443,456,461,467,493,497,511,536,546,550,554,559,562,568,571,623,663,667,671,676,679,708,712,716,721,724,764,768,773,776,792,796,799,819,828,836,841,846,985,1005],{"id":45,"type":46,"markdown":47},"intro-bill","prose","Somewhere in your home there is a piece of paper, or an SMS, or a UPI payment request, that says something like **\"Units consumed: 312. Amount payable: ₹2,184.\"** Most people glance at the rupees and move on. This layer is about everything hiding behind those two numbers.\n\nWhat exactly is a \"unit\"? Why does the air conditioner cost more than every other appliance put together, while a phone charger barely registers? Why is a 9 V battery safe for school experiments while the 230 V in a wall socket can kill, and why does it matter so much whether your hands are wet? What is the extra, fatter pin on an Indian plug actually for? And why are electricity companies starting to charge different prices at different times of day?",{"id":49,"type":46,"markdown":50},"intro-shape","You already know the three big ideas from earlier layers: **voltage** is the push, **current** is the flow of charge, and **resistance** is what slows the flow, linked by V = I × R. In the water picture, voltage is the pump's pressure, current is how much water flows past each second, and resistance is how narrow the pipe is.\n\nHere we add the two quantities that turn physics into money and safety: **power** (how fast energy is being delivered) and **energy** (how much has been delivered in total). Then we use them for real: reading rating plates, running a home energy bill lab, working through the arithmetic of an electric shock, planning a home energy audit, and estimating whether rooftop solar pays for itself. We finish by looking ahead at the grid you will grow up with.",{"id":52,"type":53,"variant":54,"title":55,"markdown":56},"intro-safety","callout","careful","One rule for this whole layer","Everything about mains electricity (the 230 V from wall sockets) in this layer is for **understanding, not experimenting**. Never open plugs, sockets, switchboards or appliances, and never test anything on mains. If you want to build circuits, use batteries of 9 V or less, and ask an adult for help. Reading rating plates and meters is safe; poking at wiring is not.",{"id":58,"type":59,"title":60,"eyebrow":61,"navLabel":62},"ch1","chapter","Power: how fast energy flows","Chapter 01","1 Power",{"id":64,"type":46,"markdown":65,"help":66},"power-idea","**Power** is the rate at which energy is transferred. Its unit is the **watt (W)**, and one watt means one joule of energy every second. A 9 W LED bulb turns 9 joules of electrical energy into light and a little heat every second it is on. A 2,000 W geyser turns 2,000 joules into heat every second, which is why it warms a bucket of water in minutes.\n\nFor electricity there is a beautifully simple formula:\n\n**power = voltage × current**, or **P = V × I**\n\nThink about why. Voltage tells you how much energy each coulomb of charge carries (1 volt = 1 joule per coulomb). Current tells you how many coulombs pass each second (1 amp = 1 coulomb per second). Multiply them and the coulombs cancel: joules per coulomb × coulombs per second = **joules per second**, which is watts.\n\nIn the water picture, power is like the pressure of the water multiplied by how much flows each second. A thin jet at high pressure and a wide, lazy river can deliver the same power in very different ways.",{"simplerExplanation":67,"anotherExample":68,"hints":69},"Voltage is how much energy each bit of charge carries. Current is how many bits pass each second. Multiply them and you get how much energy arrives each second: that is power, measured in watts.","A phone charger might give out 5 V at 2 A. Power = 5 × 2 = 10 W. A fast charger giving 9 V at 2 A delivers 18 W, so the phone fills almost twice as fast.",[70,71],"1 W = 1 J per second.","Check the units: (J\u002FC) × (C\u002Fs) = J\u002Fs.",{"id":73,"type":74,"items":75},"power-formulas","formulas",[76,79,82,85],{"expression":77,"caption":78},"P = V × I","Power in watts = voltage in volts × current in amps.",{"expression":80,"caption":81},"I = P ÷ V","Rearranged: the current an appliance draws from its wattage. At 230 V, every 230 W is 1 A.",{"expression":83,"caption":84},"E = P × t","Energy = power × time. Use kW and hours to get kWh, the \"unit\" on your bill.",{"expression":86,"caption":87},"1 kWh = 3.6 million J","1,000 J every second for 3,600 seconds.",{"id":89,"type":90,"title":91,"note":92,"scale":93,"rungs":94},"power-ladder","ladder","A ladder of power: from a charger on standby to a power station","Typical values, rounded. Each step up the log scale is roughly ten times more power.","log",[95,99,103,107,111,115,119,123,127,131,135],{"label":96,"value":97,"display":98},"Charger left plugged in, no phone",0.3,"≈ 0.3 W",{"label":100,"value":101,"display":102},"LED bulb",9,"9 W",{"label":104,"value":105,"display":106},"Ceiling fan",75,"≈ 75 W",{"label":108,"value":109,"display":110},"LED television",80,"≈ 80 W",{"label":112,"value":113,"display":114},"Mixer-grinder (mixie)",500,"≈ 500 W",{"label":116,"value":117,"display":118},"1 HP water pump",750,"≈ 750 W",{"label":120,"value":121,"display":122},"1.5-tonne air conditioner",1500,"≈ 1.5 kW",{"label":124,"value":125,"display":126},"Geyser (water heater)",2000,"≈ 2 kW",{"label":128,"value":129,"display":130},"Home EV charger",7400,"≈ 7.4 kW",{"label":132,"value":133,"display":134},"Electric passenger locomotive",5000000,"≈ 5 MW",{"label":136,"value":137,"display":138},"One large coal-power unit",800000000,"800 MW",{"id":140,"type":141,"title":142,"problem":143,"steps":144,"help":150},"power-current-example","worked_example","How much current does each appliance draw?","Indian mains is about 230 V. Find the current drawn by a 9 W LED bulb, a 75 W fan and a 2,000 W geyser.",[145,146,147,148,149],"Use I = P ÷ V.","LED bulb: 9 ÷ 230 ≈ 0.039 A, which is about 39 mA.","Fan: 75 ÷ 230 ≈ 0.33 A.","Geyser: 2,000 ÷ 230 ≈ 8.7 A.","The geyser draws over 200 times the current of the bulb. That is why big heating appliances go on the larger 16 A sockets and have thicker cables: more current means more heating in the wires (P = I² × R), so the wiring must be sized for it.",{"simplerExplanation":151,"hints":152},"Divide the watts by 230. Small numbers of watts mean a tiny current; thousands of watts mean several amps.",[153],"At 230 V, 230 W draws exactly 1 A. Use that as a quick mental check.",{"id":155,"type":53,"variant":156,"title":157,"markdown":158},"power-aha","aha","Watts are a speed, not an amount","A watt is like kilometres per hour: it tells you **how fast** energy flows, not how much has flowed. Saying \"my fan used 75 watts yesterday\" is like saying \"I travelled 60 km\u002Fh to school\". To know the amount, you also need the time. That is exactly what the next chapter adds.",{"id":160,"type":59,"title":161,"eyebrow":162,"navLabel":163},"ch2","The unit on your bill: one kilowatt-hour","Chapter 02","2 The unit",{"id":165,"type":46,"markdown":166,"help":167},"kwh-idea","Energy = power × time. If you measure power in joules per second and time in seconds, you get joules. But a joule is tiny: a 2 kW geyser uses 7.2 million of them in one hour. Numbers that big are clumsy on a bill.\n\nSo electricity companies use a bigger unit: the **kilowatt-hour (kWh)**. One kilowatt-hour is the energy used when **1,000 W runs for 1 hour**. In India, one kWh is simply called **one unit**. When your bill says 312 units, it means 312 kWh.\n\nThe recipe is always the same:\n\n**units (kWh) = watts × hours ÷ 1,000**\n\nDivide by 1,000 because the unit is based on kilowatts, not watts. The time must be in **hours**.",{"simplerExplanation":168,"anotherExample":169},"Multiply the watts by the hours it runs, then divide by 1,000. That gives the number of units. A 1,000 W appliance running for one hour uses exactly one unit.","A 100 W bulb for 10 hours: 100 × 10 ÷ 1,000 = 1 unit. A 2,000 W geyser for 30 minutes: 2,000 × 0.5 ÷ 1,000 = 1 unit. Very different appliances, same energy.",{"id":171,"type":172,"tone":173,"items":174},"unit-spec","spec","amber",[175,179,183,187,191,195],{"label":176,"big":177,"value":178},"One unit","1 kWh","The energy used by **1,000 W running for 1 hour**.",{"label":180,"big":181,"value":182},"In joules","3.6 MJ","1,000 J\u002Fs × 3,600 s = 3,600,000 J.",{"label":184,"big":185,"value":186},"Recipe","W × h ÷ 1000","Watts × hours ÷ 1,000 = units. Time must be in hours.",{"label":188,"big":189,"value":190},"Same unit, many ways","= 1 unit","100 W for 10 h, 50 W for 20 h, 2 kW for 30 min or 9 W for about 111 h.",{"label":192,"big":193,"value":194},"Example tariff","≈ ₹7","A round figure used in this layer. Real prices vary by state and by how many units you use.",{"label":196,"big":197,"value":198},"What the meter counts","kWh","Your meter adds up energy, not power. It keeps counting as long as anything draws current.",{"id":200,"type":141,"title":201,"problem":202,"steps":203},"ac-example","The air conditioner on a summer night","A 1.5 kW air conditioner runs for 8 hours every night. How many units does it use in one night, and in a 30-day month? What does that cost at ₹7 per unit?",[204,205,206,207,208],"Power is already in kilowatts: 1.5 kW.","One night: 1.5 kW × 8 h = **12 kWh = 12 units**.","Cost per night: 12 × ₹7 = **₹84**.","A 30-day month: 12 × 30 = **360 units**, costing 360 × ₹7 = **₹2,520**.","Reality check: an AC's compressor switches down or off when the room reaches the set temperature, especially inverter ACs, so the real figure is often lower. Rating-plate watts give an upper-end estimate.",{"id":210,"type":141,"title":211,"problem":212,"steps":213},"fan-example","A ceiling fan all day","A 60 W ceiling fan runs for 12 hours a day. How many units does it use per day and per 30-day month, and what does the month cost at ₹7 per unit?",[214,215,216,217],"Units per day = 60 × 12 ÷ 1,000 = 720 ÷ 1,000 = **0.72 units**.","Per month: 0.72 × 30 = **21.6 units**.","Cost: 21.6 × ₹7 = **₹151.20** a month.","Compare: the AC used 12 units in one night. The fan needs about 17 days to use that much (12 ÷ 0.72 ≈ 16.7). Fans are cheap to run; cooling air is expensive.",{"id":219,"type":141,"title":220,"problem":221,"steps":222,"help":228},"led-example","LED versus an old incandescent bulb","An old 60 W incandescent bulb and a 9 W LED give roughly the same amount of light. Each is used 6 hours a day for a year (365 days). How many units does each use, and how much does switching save at ₹7 per unit?",[223,224,225,226,227],"Incandescent: 60 × 6 × 365 ÷ 1,000 = **131.4 units** a year.","LED: 9 × 6 × 365 ÷ 1,000 = **19.71 units** a year.","Units saved: 131.4 − 19.71 = **111.69 units**.","Money saved: 111.69 × ₹7 ≈ **₹782 per bulb per year**.","Why so big a difference? An incandescent bulb makes light by heating a thin wire until it glows, and roughly 90% or more of its energy comes out as heat, not light. An LED makes light directly from electrons crossing a junction in a semiconductor, so far less is wasted.",{"simplerExplanation":229,"hints":230},"The LED uses 9 W instead of 60 W, so it uses less than a sixth of the energy for the same light. Over a year of evenings that adds up to more than 100 units per bulb.",[231,232],"Work out units for one bulb first, then the other, then subtract.","Do the subtraction before multiplying by ₹7, to keep the numbers simple.",{"id":234,"type":235,"itemId":236,"prompt":237,"check":238,"hints":243,"feedback":246},"units-practice","practice","electricity.extend-units-mixie","A 500 W mixie runs for 15 minutes a day. How many units does it use in a 30-day month?",{"kind":239,"answer":240,"tolerance":241,"unit":242},"number",3.75,0.01,"units (kWh)",[244,245],"15 minutes is 0.25 hours.","Units per day = 500 × 0.25 ÷ 1,000.",{"correct":247,"incorrect":248},"Right: 500 × 0.25 ÷ 1,000 = 0.125 units a day, and × 30 = 3.75 units a month, about ₹26 at ₹7 per unit. Powerful but brief appliances often use surprisingly little.","Convert minutes to hours first: 15 min = 0.25 h. Then 500 × 0.25 ÷ 1,000 = 0.125 units a day, and 0.125 × 30 = 3.75 units a month.",{"id":250,"type":53,"variant":251,"title":252,"markdown":253},"units-misconception","misconception","\"Bigger watts always means a bigger bill\"","Not necessarily. The bill depends on **watts × hours**. A 2,000 W geyser used for 30 minutes (1 unit) costs less per day than a 75 W fan left on for 16 hours (1.2 units). The most powerful appliance is not always the most expensive; the one that is powerful **and** runs for a long time is. That is why the AC usually wins.",{"id":255,"type":59,"title":256,"eyebrow":257,"navLabel":258},"ch3","Reading a rating plate like an engineer","Chapter 03","3 Rating plates",{"id":260,"type":46,"markdown":261},"plate-intro","Almost every appliance carries a **rating plate**: a sticker or stamped metal label, usually on the back, the bottom or inside a door. It is the appliance's passport. It tells an electrician, a shopkeeper or a curious learner what the appliance expects from the supply and how much it will take.\n\nLet's read a full plate from an imaginary but typical 15-litre geyser, line by line. (Only ever read a plate on an appliance that is switched off and cool, and never unscrew covers to find one.)",{"id":263,"type":264,"caption":265,"columns":266,"rows":270},"plate-table","table","A typical geyser rating plate, decoded",[267,268,269],"Marking on the plate","What it means","What you can work out",[271,275,279,283,287,291,295,299],[272,273,274],"**230 V ~**","Designed for 230 volts. The wavy line ~ means alternating current (AC).","It matches Indian mains. In the USA (120 V) it would not work properly.",[276,277,278],"**50 Hz**","The AC supply reverses direction 50 times each way per second.","Matches India. Many countries, like the USA, use 60 Hz.",[280,281,282],"**2000 W**","Rated power: the rate it uses energy when heating.","Current = 2,000 ÷ 230 ≈ 8.7 A, so it needs a 16 A socket and circuit. Each hour of heating = 2 units.",[284,285,286],"**15 L**","Tank capacity.","Helps compare heating time between models.",[288,289,290],"**IPX4**","Ingress protection: the X means dust protection was not rated; 4 means protected against splashing water.","Suitable for a bathroom wall, but not for being sprayed or submerged.",[292,293,294],"**ISI mark with IS number**","Certified to an Indian Standard by the Bureau of Indian Standards.","A basic quality and safety check. Avoid uncertified heating appliances.",[296,297,298],"**Model and serial number**","Identify the exact product.","Needed for warranty claims and to look up the star label and manual.",[300,301,302],"**Earth symbol ⏚**","The metal body is designed to be connected to earth.","It must use a 3-pin plug in a properly earthed socket.",{"id":304,"type":53,"variant":305,"title":306,"markdown":307},"plate-double-insulated","nuance","Two squares instead of an earth symbol","Some appliances, like many phone chargers and hair dryers, show a small square inside a larger square. That means **double insulated**: every live part is wrapped in two separate layers of insulation, so no metal you can touch could become live even if one layer fails. These appliances are designed to work safely with a 2-pin plug and no earth wire.",{"id":309,"type":235,"itemId":310,"prompt":311,"check":312,"hints":316,"feedback":319},"plate-practice","electricity.extend-plate-current","A microwave's rating plate says **230 V ~ 50 Hz, 1,150 W**. What current does it draw, in amps?",{"kind":239,"answer":313,"tolerance":314,"unit":315},5,0.05,"A",[317,318],"I = P ÷ V.","1,150 ÷ 230 = ?",{"correct":320,"incorrect":321},"Yes: 1,150 ÷ 230 = 5 A. That is fine for a 16 A socket, but it is close to the limit of a small 6 A socket once anything else is sharing it.","Divide watts by volts: 1,150 ÷ 230 = 5 A.",{"id":323,"type":53,"variant":324,"title":325,"markdown":326},"plate-model-limit","model_limit","Rated power is not always running power","The watts on a plate are the **maximum or rated** power. A fridge's compressor switches on and off all day; an AC throttles down once the room is cool; a geyser's thermostat cuts out when the water is hot; a fan on speed 2 uses less than on speed 5. Rating-plate watts × hours gives an **upper estimate**. For a real figure, read the kWh on your meter before and after, or use the yearly energy figure printed on the star label.",{"id":328,"type":59,"title":329,"eyebrow":330,"navLabel":331},"ch4","Your home's bill, appliance by appliance","Chapter 04","4 Your bill",{"id":333,"type":46,"markdown":334},"bill-intro","Time to put it all together. Below is a typical Indian home: three ceiling fans, six LED lights, a fridge, a TV, a geyser, a 1.5-tonne split AC, a 1 HP water pump that fills the rooftop tank, a mixie, and two phone chargers. Each has a power rating and a guess at daily hours.\n\nThe fridge is listed at **40 W for 24 hours**. That is not its rating-plate figure (the compressor might be rated 100–200 W) but its **average** over a day while the compressor cycles on and off, which works out to about 1 unit a day, a realistic figure for a family fridge.\n\nBefore you touch the lab, make a prediction.",{"id":336,"type":337,"prompt":338,"options":339,"explanation":352},"bill-prediction","prediction","In this home, which single appliance do you think uses the most units in a month?",[340,343,346,349],{"id":341,"label":342},"fans","The three ceiling fans (on 10 hours a day)",{"id":344,"label":345},"fridge","The fridge (on all day and night)",{"id":347,"label":348},"geyser","The 2,000 W geyser (30 minutes a day)",{"id":350,"label":351},"ac","The 1.5 kW air conditioner (6 hours a day)","The AC wins by a mile: 1,500 W × 6 h × 30 days ÷ 1,000 = **270 units**, more than everything else combined. The fans come second (67.5 units), because there are three of them running 10 hours a day. The fridge runs longest but at a low average power (28.8 units), and the geyser is powerful but brief (30 units).",{"id":354,"type":355,"component":356,"componentVersion":5,"config":357,"objective":392,"textAlternative":393,"help":394},"bill-lab","interactive","energy-bill",{"currency":358,"tariff":359,"days":360,"appliances":361},"₹",7,30,[362,366,370,373,376,379,381,384,388],{"id":341,"label":104,"watts":105,"hoursPerDay":363,"count":364,"on":365},10,3,true,{"id":367,"label":368,"watts":101,"hoursPerDay":369,"count":369,"on":365},"leds","LED light",6,{"id":344,"label":371,"watts":18,"hoursPerDay":372,"count":5,"on":365},"Fridge (average draw)",24,{"id":374,"label":375,"watts":109,"hoursPerDay":313,"count":5,"on":365},"tv","LED TV",{"id":347,"label":377,"watts":125,"hoursPerDay":378,"count":5,"on":365},"Geyser",0.5,{"id":350,"label":380,"watts":121,"hoursPerDay":369,"count":5,"on":365},"Air conditioner (1.5 t)",{"id":382,"label":383,"watts":117,"hoursPerDay":378,"count":5,"on":365},"pump","Water pump (1 HP)",{"id":385,"label":386,"watts":113,"hoursPerDay":387,"count":5,"on":365},"mixie","Mixie",0.25,{"id":389,"label":390,"watts":363,"hoursPerDay":364,"count":391,"on":365},"chargers","Phone charger",2,"Build a month's electricity bill from each appliance's watts, hours and count, and find which appliances matter most.","The lab lists nine appliances for a 30-day month at a flat ₹7 per unit, using units = watts × count × hours × days ÷ 1,000. Fans: 75 W × 3 × 10 h → 67.5 units. LED lights: 9 W × 6 × 6 h → 9.72 units. Fridge: 40 W average × 24 h → 28.8 units. TV: 80 W × 5 h → 12 units. Geyser: 2,000 W × 0.5 h → 30 units. AC: 1,500 W × 6 h → 270 units. Water pump: 750 W × 0.5 h → 11.25 units. Mixie: 500 W × 0.25 h → 3.75 units. Two chargers: 10 W × 3 h → 1.8 units. Total ≈ 434.8 units, costing about ₹3,044. The AC alone is 270 units, about 62% of the total. Switching the AC off drops the month to about 164.8 units, roughly ₹1,154. Cutting AC use from 6 to 4 hours saves 90 units (₹630). The six LEDs together use less than 10 units, and the chargers under 2: small appliances barely matter; long-running powerful ones dominate.",{"simplerExplanation":395,"hints":396},"Each appliance's monthly units are its watts times its hours times 30, divided by 1,000. Add them up and multiply by ₹7. Try switching things off to see which ones change the bill most.",[397,398,399],"Switch the AC off first and watch the total.","Then try halving the fans' hours. Which saves more: that, or switching off all the LEDs?","Set the AC to 1 hour a day. How close does the bill get to the no-AC total?",{"id":401,"type":53,"variant":54,"title":402,"markdown":403},"bill-slabs","Real bills are not flat-rate","The lab charges a flat ₹7 for every unit. Real Indian tariffs are set by each state's electricity regulatory commission and your distribution company (DISCOM), and they are usually **slabbed**: the first block of units each month is cheaper, and the price per unit rises as you use more. Bills also add a **fixed charge** (based on your connected load), **electricity duty** or taxes, and sometimes fuel-cost adjustments, while some states give free or subsidised units. Rates can differ a lot between states. In several states the cheapest slab is under ₹6 a unit while the highest is ₹14 or more, so a heavy user pays far more per unit than a flat ₹7 suggests. Use ₹7 as a round number for learning, and your own bill's tariff table for the real thing.",{"id":405,"type":141,"title":406,"problem":407,"steps":408},"slab-example","How a slabbed tariff works (made-up slabs)","Imagine a DISCOM charges ₹4 per unit for the first 100 units, ₹6 per unit for units 101–300, and ₹8 per unit above 300. What is the energy charge for 434.8 units? (These slabs are invented to show the method.)",[409,410,411,412,413],"First slab: 100 units × ₹4 = ₹400.","Second slab: the next 200 units (101 to 300) × ₹6 = ₹1,200.","Top slab: the remaining 434.8 − 300 = 134.8 units × ₹8 = ₹1,078.40.","Energy charge = 400 + 1,200 + 1,078.40 = **₹2,678.40**, before fixed charges and duty.","Notice that the last units cost the most. Cutting 100 units of AC use would save 100 × ₹8 = ₹800 here, more than the flat-rate lab suggests (₹700).",{"id":415,"type":59,"title":416,"eyebrow":417,"navLabel":418},"ch5","Stars, standby and smarter choices","Chapter 05","5 Stars and standby",{"id":420,"type":46,"markdown":421},"star-labels","Walk into any appliance shop in India and you will see coloured labels with **1 to 5 stars** on fridges, ACs, geysers, ceiling fans, washing machines, TVs and more. These come from the **Bureau of Energy Efficiency (BEE)**, part of the Ministry of Power, under its Standards and Labelling programme.\n\nMore stars mean the appliance does the same job with less electricity. The label usually also shows an **energy figure**, such as the units a fridge is expected to use in a year under standard test conditions, or an efficiency number for an AC. That figure is far more useful than the star count alone, because it lets you do real arithmetic.\n\nTwo things to know as a smart buyer:\n\n- **Compare like with like.** A 5-star 1-tonne AC and a 3-star 2-tonne AC do not do the same job.\n- **Stars are relative.** BEE revises the rating tables from time to time, so a 3-star label printed today can be better than a 5-star label from years ago. Check the label's validity year.",{"id":423,"type":141,"title":424,"problem":425,"steps":426},"star-example","Is the 5-star fridge worth the extra price?","Fridge A (3-star) is labelled at 300 units a year. Fridge B (5-star) is labelled at 200 units a year and costs ₹3,500 more. At ₹7 per unit, how long before B's savings pay back the extra price?",[427,428,429,430,431],"Units saved per year: 300 − 200 = 100 units.","Money saved per year: 100 × ₹7 = ₹700.","Payback time: ₹3,500 ÷ ₹700 per year = **5 years**.","A fridge often lasts 10 years or more, so over its life B saves about ₹7,000, twice its extra cost. If your tariff is higher (a top slab of ₹8–9), payback is even quicker.","These label figures are simplified: real use depends on room temperature, how often the door opens, and how full the fridge is.",{"id":433,"type":46,"markdown":434,"help":435},"standby-prose","Now for the sneaky one: **standby power**. Many devices keep drawing a little power even when they look \"off\": the TV waiting for the remote, the set-top box keeping its clock and updates going, the microwave's display, chargers left in the socket, the Wi-Fi router, the AC's control board.\n\nEach one might use less than 1 W to several watts. That sounds like nothing, but standby never sleeps. It runs **24 hours a day, 365 days a year**, which is 8,760 hours.\n\n**1 W of continuous standby = 1 × 8,760 ÷ 1,000 = 8.76 units a year**, about ₹61 at ₹7 per unit.\n\nA home with 20 W of standby scattered across its gadgets wastes about 175 units a year, around ₹1,226, for doing nothing at all. Researchers estimate standby is typically **5–10% of household electricity** in many developed countries.",{"simplerExplanation":436,"anotherExample":437},"Something using just 1 W, all day every day, still adds up to almost 9 units a year. Twenty small gadgets on standby can quietly cost over a thousand rupees a year.","A set-top box drawing 8 W on standby for 20 hours a day uses 8 × 20 × 365 ÷ 1,000 = 58.4 units a year, about ₹409.",{"id":439,"type":53,"variant":440,"title":441,"markdown":442},"standby-try","try_it","Hunt the glowing dots","Tonight, with an adult, turn off the room lights and look around your home for little LEDs, clocks and displays that stay lit. Each one is a device on standby. Make a list. Then look up (or ask) which ones could simply be switched off at the wall socket switch when not in use. Do **not** unplug anything with wet hands, and leave the fridge, router and anything medical alone.",{"id":444,"type":235,"itemId":445,"prompt":446,"check":447,"hints":450,"feedback":453},"standby-practice","electricity.extend-standby-year","A home's gadgets draw a total of 15 W on standby, all day, every day. How many units is that in a 365-day year?",{"kind":239,"answer":448,"tolerance":449,"unit":242},131.4,0.2,[451,452],"Hours in a year: 24 × 365 = 8,760.","Units = 15 × 8,760 ÷ 1,000.",{"correct":454,"incorrect":455},"Correct: 15 × 8,760 ÷ 1,000 = 131.4 units, about ₹920 a year at ₹7 per unit. That is roughly the same as running an old 60 W bulb 6 hours a day for a year.","Standby runs all year: 15 W × 8,760 h = 131,400 Wh = 131.4 units.",{"id":457,"type":59,"title":458,"eyebrow":459,"navLabel":460},"ch6","Why current, not voltage alone, injures","Chapter 06","6 Why current hurts",{"id":462,"type":46,"markdown":463,"help":464},"shock-idea","You will often hear \"it's not the volts that kill you, it's the amps\". That is half right. What harms the body is **current flowing through it**: charge pushing through nerves, muscles and the heart. Your nerves and heart run on tiny electrical signals. A current from outside can swamp those signals: muscles clench and won't release, breathing can stop, and the heart's steady rhythm can collapse into a useless quiver called **ventricular fibrillation**. Large currents also burn tissue from the inside, just as a geyser element heats water.\n\nBut current does not appear on its own. Something has to **push** it through you, and that something is voltage. How much current flows depends on both:\n\n**current through the body = voltage ÷ body resistance** (Ohm's law, I = V ÷ R)\n\nSo the honest version is: **voltage drives it, resistance limits it, current does the damage.** Most of your body's resistance is in your **skin**. Inside, you are mostly salty water, which conducts quite well.",{"simplerExplanation":465,"anotherExample":466},"Electricity hurts you when a current flows through your body. The voltage is the push that makes it flow. Dry skin resists that push strongly; wet skin hardly resists at all.","The static shock from a door handle can be several thousand volts, but it carries so little charge for such a short time that the current lasts only a tiny fraction of a second. Mains at 230 V can keep a large current flowing through you for as long as you stay in contact.",{"id":468,"type":90,"title":469,"note":470,"scale":93,"rungs":471},"effects-ladder","What different currents do to a person (50 Hz AC, hand-to-hand or hand-to-foot)","Rounded bands from safety guidance. Real effects depend on the path, the duration and the person.",[472,475,478,481,485,489],{"label":473,"value":378,"display":474},"Below 1 mA: usually not felt","\u003C 1 mA",{"label":476,"value":391,"display":477},"1–5 mA: a tingle","1–5 mA",{"label":479,"value":359,"display":480},"5–10 mA: a painful shock","5–10 mA",{"label":482,"value":483,"display":484},"10–30 mA: muscles may clamp, can't let go",20,"10–30 mA",{"label":486,"value":487,"display":488},"30–100 mA: breathing and heart at serious risk",60,"30–100 mA",{"label":490,"value":491,"display":492},"100 mA+: fibrillation, fatal if it continues",200,"≥ 100 mA",{"id":494,"type":53,"variant":54,"title":495,"markdown":496},"shock-careful-small","Look how small these numbers are","A 9 W LED bulb draws about 39 mA. A ceiling fan draws about 330 mA. The line where a shock becomes seriously dangerous to the heart is around **30 mA**, less than the current through a single LED bulb, and a thousandth of what a 32 A MCB lets through before it trips. Ordinary appliances handle currents that are lethal many times over.",{"id":498,"type":337,"prompt":499,"options":500,"explanation":510},"body-prediction","Someone touches a live 230 V wire with one hand while standing barefoot on a wet bathroom floor. Compared with touching it with dry hands and rubber-soled slippers, the current through them would be:",[501,504,507],{"id":502,"label":503},"same","About the same, because the voltage is the same 230 V",{"id":505,"label":506},"double","About twice as much",{"id":508,"label":509},"hundred","Around 100 times as much","Around 100 times as much. Same voltage, but wet skin can drop the body's resistance from roughly 100,000 Ω to around 1,000 Ω, and the wet floor makes a good path to earth. By Ohm's law, a hundredth of the resistance means a hundred times the current: from about 2.3 mA (a tingle) to about 230 mA, deep in the ventricular-fibrillation band.",{"id":512,"type":355,"component":513,"componentVersion":5,"config":514,"objective":529,"textAlternative":530,"help":531},"body-lab","body-current",{"voltage":515,"conditions":516},230,[517,521,525],{"id":518,"label":519,"ohms":520},"dry","Dry skin, dry shoes (≈ 100 kΩ)",100000,{"id":522,"label":523,"ohms":524},"damp","Damp or sweaty skin (≈ 10 kΩ)",10000,{"id":526,"label":527,"ohms":528},"wet","Wet skin, bare feet on wet floor (≈ 1 kΩ)",1000,"See how the same 230 V drives wildly different currents through the body as skin resistance changes, and which effect band each falls in.","This lab applies Ohm's law, current = voltage ÷ resistance, to a person touching 230 V mains in three conditions. Dry skin and dry shoes, about 100,000 Ω: 230 ÷ 100,000 = 0.0023 A = 2.3 mA, a tingle. Damp or sweaty skin, about 10,000 Ω: 230 ÷ 10,000 = 0.023 A = 23 mA, in the 10–30 mA band where muscles may clamp and you might not be able to let go. Wet skin with bare feet on a wet floor, about 1,000 Ω: 230 ÷ 1,000 = 0.23 A = 230 mA, well above 100 mA, in the ventricular-fibrillation band and fatal if the current continues. The voltage never changes; only the resistance does. Each tenfold drop in resistance gives ten times the current, and moves the result up one or two danger bands. This is a very simplified model: real body resistance changes with voltage, contact area, the path through the body and time, so no condition should ever be treated as safe.",{"simplerExplanation":532,"hints":533},"Same 230 V every time. Dry skin lets through a tiny current you would feel as a tingle. Wet skin lets through a hundred times more, which can stop a heart.",[534,535],"Divide 230 by the resistance, then multiply by 1,000 to get milliamps.","Which condition first crosses 30 mA?",{"id":537,"type":141,"title":538,"problem":539,"steps":540},"wet-skin-example","The wet-skin arithmetic","Estimate the current through a person touching 230 V mains with wet skin (body resistance ≈ 1,000 Ω), and compare it with dry skin (≈ 100,000 Ω).",[541,542,543,544,545],"Wet: I = V ÷ R = 230 ÷ 1,000 = 0.23 A.","Convert to milliamps: 0.23 A × 1,000 = **230 mA**.","That is more than seven times the ~30 mA level where the heart is at serious risk, and well past 100 mA, the band where ventricular fibrillation sets in and the shock is fatal if the current continues.","Dry: 230 ÷ 100,000 = 0.0023 A = **2.3 mA**, a tingle.","Ratio: 230 mA ÷ 2.3 mA = **100**. Water turned a tingle into a potentially fatal shock without changing the voltage at all. This is why switches, sockets and hairdryers must be kept away from water, and why you should dry your hands before touching anything electrical.",{"id":547,"type":53,"variant":324,"title":548,"markdown":549},"shock-model-limit","Why these numbers are only a sketch","Body resistance is not a fixed number. It falls as voltage rises (high voltage can break down the skin), falls with larger contact areas and longer contact, and depends on the **path**: current from hand to hand or hand to foot crosses the chest and the heart, which is the worst case. Time matters too: a current that is survivable for a few milliseconds can be fatal over a second. The values 100 kΩ, 10 kΩ and 1 kΩ are round figures for teaching. The only safe conclusion is: **treat every mains contact as potentially deadly.**",{"id":551,"type":53,"variant":305,"title":552,"markdown":553},"battery-nuance","So why are batteries safe to experiment with?","A 1.5 V or 9 V battery simply cannot push much current through dry skin: 9 V ÷ 100,000 Ω is about 0.09 mA, far below what you can even feel. That is why school circuits use low-voltage batteries. It is also why the 25 kV overhead wires on Indian railways and metro lines are deadly even without touching them: at that voltage, electricity can jump through the air across a gap to someone who gets too close, for example by climbing onto a train roof.",{"id":555,"type":59,"title":556,"eyebrow":557,"navLabel":558},"ch7","Live, neutral, earth and the devices that protect you","Chapter 07","7 Earth and breakers",{"id":560,"type":46,"markdown":561},"three-wires","Most sockets in an Indian home have three holes, fed by three wires:\n\n- **Live (phase)**, usually red or brown insulation: the wire at 230 V AC relative to the ground. It is the dangerous one.\n- **Neutral**, usually black or blue: the return path, kept close to earth potential at your local transformer.\n- **Earth**, green or green-and-yellow: normally carries no current at all. It is a safety wire, connected to the metal body of appliances at one end and to a metal plate or rod buried in the ground (the **earth pit**) at the other.\n\nIn normal use, current flows out along live, through the appliance, and back along neutral. Earth just waits.\n\nNow imagine a fault: inside a geyser, a worn wire touches the metal case. Without an earth wire, the case would sit at 230 V, waiting for someone to touch it and complete the circuit through their body. **With** an earth wire, the case is joined to the ground by a thick, low-resistance path. A large fault current rushes down the earth wire instead, which trips the MCB or blows the fuse within a fraction of a second, cutting off the supply.",{"id":563,"type":564,"diagram":565,"caption":566,"alt":567},"plug-diagram","diagram","plug-and-earth","An Indian 3-pin plug and socket: live, neutral and the longer, thicker earth pin, with the earth wire joined to the appliance's metal case.","Diagram of an Indian three-pin plug and socket. Two thinner pins at the bottom are labelled live and neutral. A single longer, thicker pin at the top is labelled earth. Inside the appliance, the live and neutral wires go to the working parts, while the green earth wire is fixed to the metal case. From the socket, the earth wire runs down to a buried earth plate. A fault path is shown: if live touches the case, current flows away through the earth wire, not through a person.",{"id":569,"type":46,"markdown":570},"earth-pin","Look closely at an Indian 3-pin plug (the 6 A and larger 16 A types) and you will notice the earth pin is **longer and thicker** than the other two. Both details are deliberate.\n\n- **Longer:** when you push the plug in, the earth pin touches first; when you pull it out, the earth pin leaves last. So the metal case is always earthed before live can reach it, and stays earthed until live has gone.\n- **Thicker:** it cannot be pushed into the live or neutral holes by mistake, and there is no way to put the plug in wrongly. On many sockets, the earth pin pushes open plastic **shutters** that cover the live and neutral holes, so a child poking a hairpin into an empty socket hits plastic, not metal.\n\nThis is why you should **never** break off or bend an earth pin to force a plug into a 2-pin socket, and never use cheap adapters that leave the earth unconnected.",{"id":572,"type":573,"title":574,"prompt":575,"options":576},"fault-explorer","explorer","What happens in a fault?","Pick a situation to follow the current and see which protection acts.",[577,589,600,611],{"id":578,"label":579,"chain":580,"badge":585,"note":588},"short","Short circuit",[581,582,583,584],"Live touches neutral","Resistance near zero","Huge current","MCB trips in milliseconds",{"text":586,"tone":587},"MCB or fuse protects the wiring","yes","A damaged cable lets live touch neutral directly. With almost no resistance, the current shoots up to hundreds of amps. The MCB's magnetic trip (or a fuse) opens the circuit almost instantly, before the wires overheat and start a fire.",{"id":590,"label":591,"chain":592,"badge":597,"note":599},"earthed-case","Earthed metal case",[593,594,595,596],"Live touches metal case","Case joined to earth","Large current to earth","MCB trips, RCCB too",{"text":598,"tone":587},"Earth wire keeps the case safe","Because the case is earthed, the fault current takes the easy path down the earth wire. It is large enough to trip the MCB, and the RCCB sees current leaving on live that never returns on neutral, so it trips too. Anyone touching the case is bypassed by a far easier path.",{"id":601,"label":602,"chain":603,"badge":608,"note":610},"person","Person touches live",[604,605,606,607],"Live touches person","Current through body to ground","Leak of 30 mA or more","RCCB trips fast",{"text":609,"tone":587},"Only the RCCB can see this","A current of, say, 230 mA through a person is tiny compared with an MCB's 16 A trip level, so the MCB does nothing. But the RCCB compares live and neutral: 230 mA going out that never comes back is a big imbalance, and it trips within a fraction of a second. It does not stop the shock starting, but it cuts it short, which is what saves lives.",{"id":612,"label":613,"chain":614,"badge":619,"note":622},"both","Touching live and neutral",[615,616,617,618],"One hand on live","Other hand on neutral","Current in = current out","RCCB sees no leak",{"text":620,"tone":621},"No device can reliably help","no","If a person completes the circuit between live and neutral with no path to earth, they look just like an appliance. What goes out on live comes back on neutral, so the RCCB sees no imbalance, and the current is far too small for the MCB. This is why switching off the supply before any work, and leaving wiring to licensed electricians, is the real protection.",{"id":624,"type":264,"caption":625,"columns":626,"rows":632},"protection-table","Fuses, MCBs and RCCBs compared",[627,628,629,630,631],"Device","What it watches","When it acts","Protects mainly","After it acts",[633,639,645,651,657],[634,635,636,637,638],"**Fuse**","Current in one wire","A thin wire melts when current stays above its rating","Wiring and appliances, from overload and short circuits (fire risk)","Must be replaced with the same rating, never with thicker wire",[640,641,642,643,644],"**MCB** (miniature circuit breaker)","Current in one circuit","Trips on overload (heat-sensing) or on a short circuit (magnetic), at ratings like 6, 10, 16 or 32 A","Wiring, from overheating and fire","Find the cause, then switch it back on",[646,647,648,649,650],"**RCCB** (residual current circuit breaker)","The **difference** between live and neutral current","Trips when about **30 mA** or more leaks away (the usual rating for homes), within a fraction of a second","**People**, from shocks through the body to earth; also leakage fires","Find the fault; press the test button monthly to check it works",[652,653,654,655,656],"**ELCB** (earth leakage circuit breaker)","Older name, often used for leakage breakers in general","Older voltage-sensing types watched the earth wire; modern homes use current-sensing RCCBs","People, from earth leakage","Many electricians recommend replacing old voltage-type ELCBs with RCCBs",[658,659,660,661,662],"**RCBO**","Both overcurrent and leakage","Combines an MCB and an RCCB in one device","Wiring and people","Common on new boards, one per circuit",{"id":664,"type":53,"variant":251,"title":665,"markdown":666},"mcb-misconception","\"The MCB will protect me from a shock\"","It won't. An MCB is rated in **amps**; a deadly shock is measured in **milliamps**. A 16 A MCB would need a current about 70 times larger than the 230 mA wet-skin shock before it even noticed. MCBs and fuses protect **wires and buildings** from overheating. The device designed to protect **people** is the RCCB (or RCBO), which is why electrical codes increasingly require one on home circuits, especially for bathrooms and outdoor sockets.",{"id":668,"type":53,"variant":156,"title":669,"markdown":670},"rccb-aha","An RCCB is an accountant","An RCCB works like a very strict accountant checking a bank account. Every milliamp that goes out on the live wire should come back on the neutral wire. Inside, both wires pass through a small magnetic ring. When the currents are equal, their magnetic effects cancel. If even 30 mA goes missing, which means it is escaping somewhere it shouldn't, perhaps through a person, the ring feels the imbalance and snaps the switch open.",{"id":672,"type":59,"title":673,"eyebrow":674,"navLabel":675},"ch8","If someone is being shocked","Chapter 08","8 Shock emergency",{"id":677,"type":46,"markdown":678},"rescue-intro","Knowing this could one day save a life, including your own. The most important thing to understand is that **a person who is being shocked is part of the live circuit**. If you grab them with your bare hands, the current can flow through you as well, and now there are two victims. Rescuers are injured this way every year.\n\nFollow these steps in order.",{"id":680,"type":681,"title":682,"items":683},"rescue-steps","steps","What to do if someone is receiving an electric shock",[684,688,692,696,700,704],{"title":685,"tag":686,"text":687},"Do not touch them","First","Never touch the person, or anything they are touching, with your bare hands while the current may still be on. Shout for help.",{"title":689,"tag":690,"text":691},"Cut the power","Fastest fix","Switch off at the main switch or MCB board, or switch off at the socket and pull the plug if you can do so safely. Cutting the supply is the safest way to free them.",{"title":693,"tag":694,"text":695},"Can't reach the switch?","Only if needed","Stand on something dry and non-conducting (a dry wooden board, rubber mat or thick dry newspapers) and push them away with a dry wooden broom handle, plastic chair or rolled-up newspaper. Never use anything wet or metal.",{"title":697,"tag":698,"text":699},"Call for emergency help","India: 112","Call 112, India's single emergency number (108 also works for ambulances in many states). Say it is an electric shock and give the address clearly.",{"title":701,"tag":702,"text":703},"Check breathing","Once free","When the person is clear of the current, check if they are breathing. If not, and someone is trained, start CPR until help arrives.",{"title":705,"tag":706,"text":707},"See a doctor anyway","Always","Anyone who has had a mains shock should be checked by a doctor, even if they seem fine. Current can disturb the heart's rhythm or cause internal burns that show up later.",{"id":709,"type":53,"variant":54,"title":710,"markdown":711},"rescue-careful","Fallen wires and high voltage: stay back","If the shock involves an overhead line, a fallen wire, a transformer or railway overhead equipment, **do not approach at all**. High voltage can jump through the air and travel across wet ground. Stay well back, at least 10 metres, keep others away, and call 112 and the electricity board. Wooden sticks do not protect you at these voltages. Only the power company can make it safe.",{"id":713,"type":714,"prompt":715},"rescue-reflection","reflection","Where is the main switch or MCB board in your home? Could you find it in the dark? Walk there with an adult this week, learn which switch is the main one, and check whether your home has an RCCB (often marked with a \"T\" test button and a 30 mA rating).",{"id":717,"type":59,"title":718,"eyebrow":719,"navLabel":720},"ch9","Project: a home energy audit","Chapter 09","9 Energy audit",{"id":722,"type":46,"markdown":723},"audit-intro","Energy auditors are professionals paid to walk through buildings, find out where the electricity goes, and recommend changes. You can do a simpler version of their job at home, with nothing more than a notebook, a phone calculator and your family's electricity meter and bills. Everything here involves **reading** labels and meters only. You never need to open, unplug or rewire anything yourself.",{"id":725,"type":681,"title":726,"items":727},"audit-steps","Your home energy audit, step by step",[728,732,736,740,744,748,752,756,760],{"title":729,"tag":730,"text":731},"Collect the last bills","Evidence","Find 6–12 months of bills (paper, SMS or the DISCOM app). Note the units each month. Which months are highest, and why might that be?",{"title":733,"tag":734,"text":735},"List every appliance","Survey","Room by room, list every appliance with an adult. Read the watts from the rating plate (or the manual) without moving or opening anything.",{"title":737,"tag":738,"text":739},"Estimate the hours","Interview","Ask family members how long each appliance runs on a typical day. Keep a tally for a few days if you can; people's guesses are often wrong.",{"title":741,"tag":742,"text":743},"Calculate units","Maths","For each appliance: watts × count × hours × 30 ÷ 1,000 = units per month. Add them up.",{"title":745,"tag":746,"text":747},"Check against the meter","Test","With an adult, note the meter's kWh reading at the same time on two days. The difference is one day's real use. How close was your estimate × 1\u002F30?",{"title":749,"tag":750,"text":751},"Find the big three","Analyse","Rank appliances by monthly units. Usually two or three appliances make up most of the bill. That is where changes matter.",{"title":753,"tag":754,"text":755},"Hunt standby","Hidden load","Count devices that stay lit or warm when \"off\". Estimate their standby watts and yearly units (watts × 8.76).",{"title":757,"tag":758,"text":759},"Propose changes","Plan","Suggest 3–5 changes with estimated savings: AC set at 24–26 °C, LEDs, switching off at the wall, shorter geyser use, a higher-star appliance when replacing.",{"title":761,"tag":762,"text":763},"Report and re-measure","Evaluate","Share your findings with the family. After a month, compare the new bill. Did the savings appear? Remember weather also changes use.",{"id":765,"type":53,"variant":305,"title":766,"markdown":767},"audit-ac-nuance","Why the AC thermostat matters so much","An AC works hardest when the outside is much hotter than the room. Setting it to 24–26 °C instead of 18–20 °C means it pumps out less heat, so the compressor runs less. India's Bureau of Energy Efficiency has promoted **24 °C as a default setting** for this reason. A ceiling fan alongside the AC lets you feel cool at a higher setting, for about 75 W instead of hundreds more.",{"id":769,"type":59,"title":770,"eyebrow":771,"navLabel":772},"ch10","Rooftop solar and the grid of the future","Chapter 10","10 Solar and future",{"id":774,"type":46,"markdown":775},"solar-intro","Solar panels turn sunlight directly into electricity. A panel is made of cells of silicon; when light hits a cell, it gives energy to electrons, and the cell's structure pushes them one way, making a direct current (DC). An **inverter** then converts that DC into 230 V, 50 Hz AC matching the grid.\n\nIndia gets a lot of sunshine, and the government runs a rooftop solar scheme (**PM Surya Ghar**) that gives homes a subsidy toward the cost. With **net metering**, units your panels produce but you don't use flow out to the grid and are credited against units you draw at night.\n\nSo, does rooftop solar pay for itself? Let's estimate, making every assumption visible.",{"id":777,"type":141,"title":778,"problem":779,"steps":780,"help":787},"solar-example","A simplified rooftop solar payback estimate","A family considers a **3 kW** rooftop system. Assumptions (all simplified): it produces about **4 units per kW per day** averaged over the year; it costs about **₹60,000 per kW** installed; a subsidy of **₹78,000** applies (the scheme's figure for 3 kW systems when announced in 2024); every unit produced saves a full **₹7**. Estimate the yearly saving and the payback time.",[781,782,783,784,785,786],"Daily generation: 3 kW × 4 units per kW = **12 units a day**.","Yearly generation: 12 × 365 = **4,380 units**.","Yearly saving: 4,380 × ₹7 = **₹30,660**.","Cost before subsidy: 3 × ₹60,000 = ₹1,80,000 (1.8 lakh). After subsidy: 1,80,000 − 78,000 = **₹1,02,000**.","Payback with subsidy: 1,02,000 ÷ 30,660 ≈ **3.3 years**. Without subsidy: 1,80,000 ÷ 30,660 ≈ **5.9 years**.","Panels are usually expected to last 25 years, so on these assumptions the system would pay for itself several times over.",{"simplerExplanation":788,"hints":789},"Work out how many units the panels make in a year, turn those into rupees saved, then divide the cost by the yearly saving. That tells you how many years until the panels have paid for themselves.",[790,791],"Payback time = cost ÷ saving per year.","₹1,02,000 is Indian notation for one lakh two thousand, 102,000.",{"id":793,"type":53,"variant":324,"title":794,"markdown":795},"solar-model-limit","What this estimate leaves out","Real payback can be longer or shorter. Generation varies by city, season, roof direction, shade and dust (clean panels matter). Panels slowly lose output, often around half a percent a year, and inverters may need replacing after 10–15 years. Net-metering rules and the price credited for exported units differ by state. A slabbed tariff means the units solar replaces may be worth more or less than ₹7. Subsidy amounts and system prices change. Treat the answer as \"a few years, not decades\", then get real quotes and your DISCOM's rules.",{"id":797,"type":46,"markdown":798},"peak-prose","Here is the grid's great puzzle. Electricity must be generated at the **same moment** it is used; the grid itself stores almost nothing. Across India, demand climbs on hot afternoons and peaks again in the **evening**, roughly 6–11 pm, when lights, TVs, fans, ACs and kitchens all run together. But solar power, now a large and fast-growing share of India's supply, fades to zero just as that evening peak arrives.\n\nIf you plot the demand that is left for other power stations after solar, it sags at midday and shoots up at sunset. Engineers call this shape the **duck curve** (it looks like a duck's belly and neck). Coal, gas and hydro plants must ramp up quickly every evening, which is costly and hard.\n\nThere are four big answers, and you will see all of them grow in your lifetime.",{"id":800,"type":681,"title":801,"items":802},"future-steps","Four ways the grid is adapting",[803,807,811,815],{"title":804,"tag":805,"text":806},"Storage","Shift energy in time","Big battery banks and pumped-hydro schemes (pumping water uphill at midday, letting it flow down through turbines at night) store cheap solar energy for the evening peak.",{"title":808,"tag":809,"text":810},"Smart meters","Measure by the hour","Digital meters record when you use electricity, not just how much, and send readings automatically. Many work in prepaid mode, like a mobile recharge.",{"title":812,"tag":813,"text":814},"Time-of-day tariffs","Price by the hour","India's 2023 rules make power 10–20% cheaper during solar hours and 10–20% dearer at peak, rolling out as smart meters are installed.",{"title":816,"tag":817,"text":818},"Electric vehicles","Load and battery","EVs add a large new demand, but if charged at midday or late night they fill the grid's quiet hours, and in future they may even feed power back at peak.",{"id":820,"type":141,"title":821,"problem":822,"steps":823},"tod-example","Shifting a load under a time-of-day tariff","Suppose the normal tariff is ₹7 per unit, solar hours are 20% cheaper and peak hours are 20% dearer. A washing machine cycle plus ironing uses 2 units. What does it cost at peak, and at midday?",[824,825,826,827],"Peak price: ₹7 × 1.2 = ₹8.40 per unit. Cost: 2 × 8.40 = **₹16.80**.","Solar-hours price: ₹7 × 0.8 = ₹5.60 per unit. Cost: 2 × 5.60 = **₹11.20**.","Saving by shifting: ₹5.60 per day, about ₹168 in a 30-day month.","The grid benefits too: that load moves from the stressed evening to the sunny hours when cheap solar is plentiful.",{"id":829,"type":141,"title":830,"problem":831,"steps":832},"ev-example","Charging an electric car at home","A small electric car has a 30 kWh battery. How long does a 3.3 kW home charger take to fill it from empty, and what does a full charge cost at ₹7 per unit?",[833,834,835],"Time = energy ÷ power = 30 kWh ÷ 3.3 kW ≈ **9.1 hours**. A little longer in practice, because some energy is lost as heat while charging.","Cost: 30 units × ₹7 = **₹210** (plus those small losses).","One full charge is 30 units, about as much as the geyser in our lab uses in a month. If many homes plug in at 7 pm, the evening peak gets much worse. Charged overnight or at midday on a time-of-day tariff, the same energy is cheaper and far easier for the grid.",{"id":837,"type":53,"variant":838,"title":839,"markdown":840},"open-questions","question","Open questions for curious learners","Nobody has fully solved these yet. Pick one and dig in.\n\n- How much battery storage would India need to run the evening peak mostly on stored solar power, and what should those batteries be made of?\n- Could millions of parked electric cars act as one giant battery for the grid without wearing out their owners' batteries?\n- Should electricity be cheaper for the first units every family uses, even if that means others pay more? What is fair?\n- Solar farms need land and panels need recycling at the end of their life. How should that be done well?\n- Why do the USA and India use different voltages and frequencies, and would it ever be worth changing?\n- If a smart meter knows when you use every appliance, who should be allowed to see that data?",{"id":842,"type":59,"title":843,"eyebrow":844,"navLabel":845},"ch11","Check yourself","Chapter 11","11 Check yourself",{"id":847,"type":848,"title":849,"questions":850},"final-quiz","quiz","Power, bills and safety quiz",[851,868,881,894,907,920,933,946,959,972],{"itemId":852,"prompt":853,"options":854,"correct":862,"why":867},"electricity.extend-q-power","A kettle draws 8 A from 230 V mains. What is its power?",[855,858,861,864],{"id":856,"label":857},"a","About 29 W",{"id":859,"label":860},"b","238 W",{"id":862,"label":863},"c","1,840 W",{"id":865,"label":866},"d","8,230 W","P = V × I = 230 × 8 = 1,840 W, about 1.8 kW. Dividing (230 ÷ 8) or adding the numbers doesn't give power.",{"itemId":869,"prompt":870,"options":871,"correct":859,"why":880},"electricity.extend-q-unit","One \"unit\" on an Indian electricity bill is:",[872,874,876,878],{"id":856,"label":873},"1 kW of power",{"id":859,"label":875},"1 kWh of energy, like 1,000 W for 1 hour",{"id":862,"label":877},"1 amp for 1 hour",{"id":865,"label":879},"Whatever the DISCOM decides it is","A unit is one kilowatt-hour, an amount of energy: 1,000 W for 1 hour, or 100 W for 10 hours. A kilowatt on its own is a rate, not an amount.",{"itemId":882,"prompt":883,"options":884,"correct":862,"why":893},"electricity.extend-q-ac","A 1.5 kW AC runs 8 hours a night. How many units does it use per night?",[885,887,889,891],{"id":856,"label":886},"1.5 units",{"id":859,"label":888},"8 units",{"id":862,"label":890},"12 units",{"id":865,"label":892},"12,000 units","1.5 kW × 8 h = 12 kWh = 12 units. (12,000 would be watt-hours, not kWh.)",{"itemId":895,"prompt":896,"options":897,"correct":859,"why":906},"electricity.extend-q-standby","Roughly how many units a year does 1 W of standby power use if it is on all the time?",[898,900,902,904],{"id":856,"label":899},"About 0.024 units",{"id":859,"label":901},"About 8.8 units",{"id":862,"label":903},"About 365 units",{"id":865,"label":905},"About 1,000 units","1 W × 24 × 365 h = 8,760 Wh ≈ 8.8 kWh. Small, but multiplied across many devices and many years it adds up.",{"itemId":908,"prompt":909,"options":910,"correct":865,"why":919},"electricity.extend-q-wet","Using a simple model, what current flows through a person with wet skin (about 1,000 Ω) who touches 230 V?",[911,913,915,917],{"id":856,"label":912},"About 0.23 mA",{"id":859,"label":914},"About 2.3 mA",{"id":862,"label":916},"About 23 mA",{"id":865,"label":918},"About 230 mA","I = V ÷ R = 230 ÷ 1,000 = 0.23 A = 230 mA, well into the ventricular-fibrillation band, which is fatal if the current continues. With dry skin (about 100 kΩ) it would be about 2.3 mA.",{"itemId":921,"prompt":922,"options":923,"correct":859,"why":932},"electricity.extend-q-injures","Which statement best explains what injures a person in an electric shock?",[924,926,928,930],{"id":856,"label":925},"High voltage alone, whatever the current",{"id":859,"label":927},"Current through the body, which voltage drives and the body's resistance limits",{"id":862,"label":929},"The frequency of the supply only",{"id":865,"label":931},"The number of watts on the appliance","Damage comes from current through nerves, muscles and the heart. Voltage is needed to push it; resistance (mostly skin) sets how much flows. A static spark has high voltage but only a very brief, tiny flow of charge.",{"itemId":934,"prompt":935,"options":936,"correct":859,"why":945},"electricity.extend-q-earthpin","Why is the earth pin on an Indian 3-pin plug longer than the others?",[937,939,941,943],{"id":856,"label":938},"So it carries more current in normal use",{"id":859,"label":940},"So it connects first and disconnects last, keeping the case earthed whenever live is connected",{"id":862,"label":942},"It is only there to hold the plug firmly",{"id":865,"label":944},"To make the plug fit American sockets","Being longer, the earth pin makes contact before live and breaks contact after it. Earth normally carries no current; it is a safety path for faults. Being thicker also stops the plug going in the wrong way and often opens the socket's safety shutters.",{"itemId":947,"prompt":948,"options":949,"correct":862,"why":958},"electricity.extend-q-rccb","Which device is designed to protect a person who touches a live wire while standing on the ground?",[950,952,954,956],{"id":856,"label":951},"A 16 A MCB",{"id":859,"label":953},"A fuse",{"id":862,"label":955},"A 30 mA RCCB",{"id":865,"label":957},"A voltage stabiliser","The RCCB compares live and neutral current and trips at about 30 mA of leakage. A shock current of a few hundred milliamps is far too small to trip a 16 A MCB or blow a fuse, which protect wiring from overheating.",{"itemId":960,"prompt":961,"options":962,"correct":862,"why":971},"electricity.extend-q-rescue","Your friend is stuck holding a faulty appliance and being shocked. What should you do first?",[963,965,967,969],{"id":856,"label":964},"Pull them away by the arm as fast as possible",{"id":859,"label":966},"Throw water on the appliance",{"id":862,"label":968},"Switch off the power at the MCB board or socket, without touching them",{"id":865,"label":970},"Wait for them to let go on their own","Cut the power first. Touching them could put you in the circuit too, and water conducts. If you truly cannot reach a switch, push them free with something dry and non-conducting, like a wooden broom handle, while standing on something dry. Then call 112.",{"itemId":973,"prompt":974,"options":975,"correct":859,"why":984},"electricity.extend-q-solar","A rooftop system saves ₹30,000 a year and costs ₹1,20,000 after subsidy. On this simple model, what is the payback time?",[976,978,980,982],{"id":856,"label":977},"About 0.25 years",{"id":859,"label":979},"About 4 years",{"id":862,"label":981},"About 12 years",{"id":865,"label":983},"About 40 years","Payback = cost ÷ yearly saving = 1,20,000 ÷ 30,000 = 4 years. Real payback depends on sunlight, tariffs, net-metering rules and panel wear.",{"id":986,"type":987,"title":988,"points":989},"cheat-sheet","summary","Cheat sheet",[990,991,992,993,994,995,996,997,998,999,1000,1001,1002,1003,1004],"**Power** is the rate of energy transfer: 1 W = 1 J per second. **P = V × I**. At 230 V, every 230 W draws 1 A.","**Energy = power × time.** Units (kWh) = watts × hours ÷ 1,000. 1 unit = 1,000 W for 1 hour = 3.6 million J.","1.5 kW AC × 8 h = 12 units. 60 W fan × 12 h = 0.72 units. A 9 W LED saves about 112 units a year over a 60 W bulb at 6 h a day.","The bill depends on **watts × hours**: powerful appliances that run for a long time (usually the AC) dominate.","Real tariffs are **slabbed**, set by state regulators and DISCOMs, with fixed charges and duty. ₹7 per unit is a round learning figure.","Rating plates show voltage (230 V ~), frequency (50 Hz), power (W), safety marks, IP rating and whether the case is earthed or double insulated.","**BEE star labels:** more stars means less energy for the same job. Use the yearly units figure to calculate payback.","**Standby:** 1 W all year ≈ 8.76 units. Many small standby loads add up.","**Current through the body injures**; voltage drives it and skin resistance limits it. 230 V ÷ 100 kΩ ≈ 2.3 mA (tingle); 230 V ÷ 1 kΩ ≈ 230 mA (ventricular fibrillation, fatal if it continues).","About 10–30 mA can stop you letting go; above about 30 mA the heart and breathing are at serious risk.","**Earth** gives fault current an easy path so the case never stays live. The earth pin is longer (first in, last out) and thicker (can't go in wrongly).","**Fuses and MCBs** protect wiring from overcurrent. **RCCBs** protect people by tripping at about 30 mA of leakage.","**Shock emergency:** don't touch; switch off at the MCB or socket; if impossible, push free with something dry and non-conducting; call **112**; see a doctor.","**Solar payback** ≈ cost after subsidy ÷ yearly saving. A simplified 3 kW example: 4,380 units a year, about ₹30,660 saved, about 3.3 years.","The **evening peak** arrives as solar fades. Storage, smart meters, **time-of-day tariffs** and smart EV charging help the grid cope.",{"id":1006,"type":1007,"sourceIds":1008},"extend-sources","sources",[1009,1010,1011,1012,1013,1014,1015],"elec-extend-physicsclassroom-power","elec-extend-bee-standards-labelling","elec-extend-lbl-standby","elec-extend-hyperphysics-shock","elec-extend-wikipedia-rcd","elec-extend-pib-tod-tariff","elec-extend-pm-surya-ghar",[1009,1010,1011,1012,1013,1014,1015],"needs_review",{"generatedBy":1019,"notes":1020},"claude-code","Draft generated locally; pending owner review.","eb0da95691faaaefc511d516acaf774d738fa487250acaac04764e62f433b92f",{"logic:practice":1023,"component:energy-bill@1":1024,"component:body-current@1":1025,"diagram:plug-and-earth":1026,"source:elec-extend-bee-standards-labelling":1027,"source:elec-extend-hyperphysics-shock":1028,"source:elec-extend-lbl-standby":1029,"source:elec-extend-physicsclassroom-power":1030,"source:elec-extend-pib-tod-tariff":1031,"source:elec-extend-pm-surya-ghar":1032,"source:elec-extend-wikipedia-rcd":1033},"3d6b0fe1b15255975a32b0fcd94e8019bc959ad45cbf12e136e86149549c6878","8a06f29b120906723238d3dfc612c4c29c1af4d7b4e89178fcee8c323ac7e3c7","f0549ba48695a6eaaed9595ef662beb1f8ecdf653291224c59ff4fd1a0fe101a","1cd52c8be2aa6e0b61a55e310a27dab02e8231f63fb2d3fea74c12408c32043e","2b323b53e41c2d6f2893df61d4ab54aa2a6cf7ca368e133e270dc65639e42af0","2e1273871e2fcf60a7d2a6b19eef8935df7a3355e17daae3169e375a5e456d84","d53681f09224ed27b54c02186e46585f8e423b9dc50c46b1c63beb32e76f2e73","705acfb20dcd993a30c2531012b760f8a862e15e0dcb9462c77bf552a433de1a","cc09fc0663a7cc0c644154abb0f26d026fd3eaa53e2819ae962543d07064f62e","595de49dc46967a956b5a0d900bc00f2cdce8ea012c5512add9ba4979a1ff4c5","126ceaf39c7afbad5b6bd110660ec57248a5f503fb8ae93522000d5df737ae7b",{"state":1035,"reviewer":1036,"selfReview":365,"reviewedAt":1037,"method":1038},"approved","The library owner","2026-09-20T10:18:37.581Z","owner_bulk","preview-7e1cbbcc4f",1789899599766]