Question

A bulb is rated 40W,220V.Find the current drawn , also find resistance.If the
given bulb is replaced by bulb of rating 25W,220V.will there be any change in the current and resistance? Determine the change

Answer 1

Given, P₁=40W V= 220V

We know, P=VI

So P₁=VI₁,

I₁= P₁/V= (40/220)= 2/11 Amp

and from Ohm's law, V= I₁R₁,   R₁= V/I₁= (220)/(2/11) = 1210 Ω

If rating of the the bulb is replaced by 25W and 220V, then

I₂= P₂/V= 25/ 220 =5/44 Amp

Now, from Ohm's law, V=I₂R₂

R₂= V/I₂= 220/ (5/44)= 1940Ω

Since rated power of the bulb is changed by changing its parameter resistance. So definitely There will be change in current.

Thus change in current, I₁-I₂= (2/11) - (5/44)= 3/44 Amp

And change in resistance is R₂-R₁= 1940-1210= 730 Ω