Question

A piece of wire of resistance 20ohm is drawn out so that its length is increased to twice its original length calculate the resistance of a wire in new situation

Answer 1

R = ρ L/A
= ρ L^2 / V

When wire is stretched volume (V) will remain constant.

∴ R ∝ L^2

If Length is increased to twice its length then resistance will increase by 4 times.

Hence,
Resistance of wire after stretched = 4 × Resistance of wire before stretched.