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(a)DEFINE ELECTRIC POWER. (b)A DEVICE OF RESISTANCE R IS CONNECTED ACROSS A SOURCE OF V VOLTAGE AND DRAWS A CURRENT I.DERIVE AN EXPRESSION FOR POWER IN TERMS V AND I. (c)AN ELECTRIC BULB IS CONNECTED TO A 220V GENERATOR .THE CURRANT IS 0.5A.WHAT IS THE POWER OF THE BULB.
(a) Electric power is the electrical work done per unit time .That is ,
Power = Workdone / Time taken
            = W/t
The S.I. unit of electric power is watt which is denoted by the letter W. The power of 1 watt is a rate of working of 1 joule per second.That is,
1 watt = 1 joule/1 second
(b)Expression for Power in terms of V and I

               We know that :
                                      Power = Work done/Time taken
or P = W/t
We have studied that the work done W by current I when it flows for time t under a potential difference V is given by :
                                             W = V x I x t joules
Putting this value of W in equation P = W/t,we get :
                                                    P = V I t / t joules per second
or                              Power,P = V x I watts
           where                        V = Potential difference (or Voltage) in volts
                 and                       I = Current in amperes
Thus,the power in watts is found by multiplying the potential difference in volts by the current in amperes.

(c) Given that                     current,I = 0.5 A
                      Potential difference,V = 220 V
                        Power of the bulb,P = VI
                                                       = 220 x 0.5
                                                       = 110 V


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