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Question

(a) Write two points of difference between electric energy and electric power (b) Out of 60w and 40w lamps which one has higher electrical resistance when in use?


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Solution

(a) Difference between electric energy and electric power.

Electric energy

Electric power

1

The work done or energy supplied by the source in maintaining the flow of electric current is called electrical energy. It appears in the form of heat given by

H=VIt=V2tR=I2RT

The time rate at which electric energy is consumed or dissipated by an electrical device is called electric power and is given by

P=VI=V2R=I2R

2It is equal to the product of power and time E=P×tIt is equal to the rate of doing work by an energy source. P=Wt
3Its SI unit is the joule (J).Its SI unit is a watt (W).

(b) To find the lamps which one has higher electrical resistance when in use

For the same applied voltage,
P=V2RP1R
The less the power of an electrical device, the higher its electrical resistance. So 40W lamp will have higher resistance.


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