Question

Copper wire of certain length and resistance is drawn out to three times its length without change in volume, the new resistance of wire becomes

Answer 1

R=ρ(l/A)

new length(l2)=3l

As it is stretched in length, the area of cross section decreases and becomes thinner

new area of cross section (A2) = A/3

new resistance = ρ(l2/A2)

                         = ρ(3l/(A/3))

                        = ρ(9l/A)

                        =9R = 9 times intial resistance