Specific Resistance - Resistivity

SPECIFIC RESISTANCE 

(RESISTIVITYρ)

Resistivity is a property of material.

Definition: Resistance per unit length per unit area of cross section of material of conductor is called specific resistance of the material.

The resistance of the given conductor depends on

1.  Nature of material of conductor

2.  Area of its cross section

3.  Its length

The resistance (R) of a conductor of uniform cross section is –

1.  Directly proportional to its length (l)

2.  Inversely proportional to its area of cross section  (A)

Thus the resistance is

                                R  l/A

                                R = ρl/A

Where ρ is the specific resistance also called resistivity

Therefore,

ρ = RA/l

The SI unit of ρ is ohm-metre (Ωm)