- Introduction
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- Electric Charges
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- Conductors and insulators
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- Electric potential and potential difference
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- Electric current and electrical circuits
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- Circuit Diagrams
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- Ohm's Law
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- Factors affecting of resistances of a conductor
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- Resistance of a system of resistors
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- Heating Effect of current
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- Applications of heating effect of current
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- Electric Power

- Electric Charge
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- Electric Potential
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- Materials(conductors, insulators & superconductors)
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- Electric Current
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- Ohm's Law

- Rate of doing work or the rate of consumption of energy is known as
**POWER**

Mathematically,

- SI unit of power is Watt which is denoted by letter W. The power of 1 Watt is a rate of working of 1 Joule per second.
Actually Watt is a small unit, therefore , a bigger unit of electric power called Kilowatt is used for commercial purposes. Also ,

1 kilowatt = 1000 Watts

So,

" the rate at which electric work is done or the rate at which electric energy is consumed is called electric power "

- We will now derive formula for the calculation of electric power.

From equation 14 we know that

Now we know that work done W by current I when it flows for time t under a potential difference V is given by

Putting this value of work done in equation 16 we get

Hence,

Electric Power = voltage x current

- From equation 17 we know that

$P=VI$

Now from Ohm's law

Putting above equation in equation 15 we get

$P=I \times R \times I$

Power , $P=I^2 \times R$ - Above formula is used to calculate power when only current and resistance are known to us.

- From equation 17 we know that P=VI
Now from Ohm's law

Or we have

- Putting this value of I in equation 15 we get

$P = V \times \frac{V}{R}$

$P = \frac{V^2}{R}$

This formula is used for calculating power when voltage*V*and resistance*R*is known to us. - It is clear from the above equation that power is inversely proportional to the the resistance.
For example , the resistance of a 100 Watt bulb (220 V) is smaller then that of 60 Watt (220 V) bulb.*Thus the resistance of high power devices is smaller then the low power ones.*

- We have three formulas for calculating electric power. These are

(1) $P = V \times I$

(2) $P= I^2 \times R$

(3)$P = \frac{V^2}{R}$

You must memorize these formulas as they would be used to solve numerical problems. - When electrical appliance consumes electrical energy at the rate of 1 Joule per second , its power is said to be 1 Watt.
- Rate at which electric work is done or the rate at which electric energy is consumed , is called electrical power.

Class 10 Maths Class 10 Science