# Find the Expression for the Resistivity of a Material and State the Si Unit of Resistivity. - Science and Technology 1

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

#### Solution

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).

Concept: Ohm’s Law
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