A piece of wire of resistance `R` is redrawn by pulling it until its length is doubled. Compare the new resistance with the original value.
Two lamps , one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to a 220 V supply. What is the current drawn from the supply line ?

Explanation

When `l` becomes `2 l`, A becomes `A//2`. New resistance, `R' = (rho(2 l))/(A//2) = 4 (rho l//A) = 4 R` (where `R = rho l//A` is the original resistance).
Since the two lamps are in parallel, total power, `P = 100 W + 60 W = 160 W`
Resistance, `R = (v^2)/(P) = ((220)^2)/(160) = 302.5 Omega`
Current, `I = (v)/( R) = (220 V)/(302.5 Omega) = 0.727 A`.