Question

A piece of wire of resistance 20 Ω is drawn out so that its length is increased to twice its original length. Calculate the resistance of the wire in the new situation.

Answer 1

We know that,

R = `rho l/A`

l' = 2l

A' = `A/2`

ρ' = ρ

∴ R' = `rho' (l')/(A')`

R' = `rho (2 l)/(A/2)`

R' = `4 rho (l/A)`

R' = 4 R

R' = 4 × 20

R' = 80 Ω    ...[R = 20 Ω]