A current of 3A flows through a metal rod od 0.20cm in diameter. The length of the rod is 1.5m and the Potential Difference between its ends is 40V. Calculate the resistivity of the material of the rod.

we have the resistance as

R = ρL/A

so, resistivity will be

ρ = AR/L

here,

R = VI = 40volts x 3amps = 120 ohms

A = πr² = 3.14 x (0.1 x 10^-2)² = 3.14 x 10^-6 m²

L =1.5m 

so,

ρ = (3.14 x 10^-6 x 120) / 1.5

thus, we have

ρ = 251.2 x 10^-6 ohm.m