Question

An electric bulb is rated 220 V and 100W. When it is operated on 110V, the power consumed will be?

solution A:
p=VI
100=220I
5/11=I

P=VI
P=110*5/11=50W

Solution 2:

Power consumed by the electric bulb, P=(V^2)/R, where V is the potential difference and R is the electrical resistance.
So, if at 220V bulb consumes 100 W,
⇒100=(220^2)/R

⇒R=(220^2)/100=484Ω

So, when it is operated at 110V,

Power consumed
=110^2/R
=110^2/484
=25W


first solution we get 50w, and the second we get 25w. so which of them is correct?
please tell, I got so confused

Answer 1

• First one is correct 50W should be the answer as P is directly proportional to V
• So when V was decreased P should also decrease
• V decreased by half so P should also decrease by half so P becomes 100/2=50W