Question

Q. A wire of length L and resistance R is stretched to get the radius of cross section halved. What is the new resistance of the wire ?

Answer 1

Let new length = l'
new Area =, A' and
new resistance = R'

Given, l' = 2l and A' = A/2

As we know

R = (ρl) / A

So, R' = [ρ × 2l] / (A/2) = (4 × ρl) / A = 4 × (ρ l / A )
but R = ρl/A

⇒ R' = 4 ×R

hope it helps