Question

a cylindrical rod is reformed to twice it's length with no change in its volume if the resistance of the rod was R the new resistance will be

Answer 1

We know , that

R is directly proportional to length provided that temperature and surface area remains constant .

→ The new resistance will be same as integral increase in length of the conductor .

→The new resistance = 2R .

Answer 2

Explanation:

Volume =πr2 = A×L

L′ =2L

⟹A′ = A/2

(Since volume is constant.)

We know,

R = ρ×L/A

Hence,

R/R′= L/L′× A/A'= 2L/L × A/A/2 = 4

Hence,

R′=4R