Question

Find the expression for the resistivity of a material and state the SI unit of resistivity.

Answer 1

The resistance of a conductor is directly proportional to its length l and inversely proportional to its area of cross-section A.

`R prop l` and `R prop 1/A`

`:. R prop l/A`

`:. R = rho 1/A`

where ρ is the proportionality constant and is called the resistivity of the material of the conductor.

Rearranging the above equation,

`rho = "RA"/l`

This is the expression for resistivity.

The SI unit of resistivity is ohm-meter (Ω.m).