What is electrical resistivity of a material ? State its SI unit and define it.

Explanation

It is found that the resistance R of a uniform metallic conductor depends on its length 1, on its area of cross-section A, the nature of its material and temperature
Precise measurements have shown that at a given temperature,
`R prop l and R prop 1/A`
Combining above two relations,
`R prop l/A`
`:. R =rho l/A` .......(12.6)
Where `rho` (rho) is a constant of proportionality and is called the electrical resistivity of the material of the conductor.
From equation (12.6)
`rho = (RA)/l ` .... ...(12.7)
`:.` The SI unit of `rho`
`= ("The SI unit of resistance "xx" The SI unit of area of cross - section")/("The SI unit of length")`
`=(Omegam^2)/m`
`=Omegam` (ohm-metre)
In equation (12.7), if A = 1 unit and l = 1 unit, `rho = R`.
The electrical resistivity of a material is the resistance of a conductor (of that material) having unit length and unit area of cross-section.
[Notes : (1) Resistivity depends on temperature.
(2) Resistivity is also called specific resistance.]