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## Class 10 Physics (India)

### Unit 3: Lesson 7

Electric power and heating effect of current

# Electric power & energy

Let's learn how to calculate electric power delivered & consumed in any circuit.  Created by Mahesh Shenoy.

## Want to join the conversation?

• 1)why is kWh a commercial unit of power?
2)does the concept of heating effect of electric current work in these LED bulbs? • 1) kWh is not the commercial unit of power. It is the commercial unit of energy. Why? Because we use a lot of energy, and watt-second (power 'watt' * time 'second') is not sufficient (or else our power bills would run into hundreds and millions of watt-seconds!)

2) Contrary to popular belief, LEDs do generate heat, even though it's much, much lesser than other traditional bulbs. Its technology uses the maximum energy applied to it and converts it into light, leaving less heat energy.

Hope this helps. :)
• At he says we don not pay for "voltage or current but energy we consume". But basically energy provided is what we call volts.
For eg:5v is equal to 5 joule of energy per coulomb • Hey there,
I had a similar question and I assume the answer is the same, quite simple really,
By energy we consume he means total energy,
Say 5V is the magnitude of the source,
that isn't the total amount of energy consumed by us but rather energy consumed for 1C,
I guess it's safe to say that no-one would use only 1C.
the total amount of energy used by a device =VQ has to be the same as total amount of energy produced (by conservation of energy).
Think about what I have replied and you may get the total answer,
Hope this helps
and if I'm wrong do let me know.
(1 vote)
• At ,he said that P=V*I. This also means that Voltage is inversely proportional to current. But ohm's law (V=I*R) tells that voltage is directly proportional to current. Isn't this a contradiction? • 1 kWh equals to? • The kilowatt hour (symbolized kW⋅h as per SI) is a composite unit of energy equivalent to one kilowatt (1 kW) of power sustained for one hour. One watt is equal to 1 J/s. One kilowatt hour is 3.6 megajoules, which is the amount of energy converted if work is done at an average rate of one thousand watts for one hour.
An electric heater consuming 1000 watts (1 kilowatt), and operating for one hour uses one kilowatt hour of energy. A television consuming 100 watts operating for 10 hours continuously uses one kilowatt hour. A 40-watt electric appliance operating continuously for 25 hours uses one kilowatt hour. In terms of human power, a healthy adult male manual laborer will perform work equal to about half a kilowatt hour over an eight-hour day.  