Consider two wires made of copper. They have the same diameter but one of them has three times the length of the other. Choose the correct statement:

a. Both wires have the same resistivity

b. The long wire has one third of the resistivity of the short wire

c. None of the other answers is correct

d. The long wire has three times the resistivity of the short wire

a. Both wires have the same resistivity

Explanation:

For the resistance of a wire, following formula holds good.

R = ρ l / S, R is resistance, l is length, S is cross sectional area and ρ is resistivity of the material that the wire is made of. Resistance is dependent on length and cross sectional area but resistivity does not depend upon length or cross sectional area. It only depends upon the type of material.

If we replace copper wire with aluminium wire, then resistivity will change.

Hence, since the wire remains made of copper, resistivity will not change.