An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, thepower consumed will be (a) 100 W (b) 75 W (c) 50 W (d) 25 W

Q.3:-  An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, thepower consumed will be –(a) 100 W (b) 75 W (c) 50 W (d) 25 W

 

Answer:- 

(d) 25w
Solution:-
R=V2/P
                 = (220)2/100
                 = 484 Ω
The resistance of the bulb remains constant
 if the supply voltage is reduced to 110 V then Vʹ=110 V
 the power consumed by it is given by the expression = Vʹ2/R
                                                                                                         = (110)2/484
                                                                                                         = 25w