What is Conductivity?

The reciprocal quantity of resistance is called conductance. Like that, the reciprocal quantity of specific resistance is called conductivity. Conductivity is expressed by the letter σ. The value of σ depends on the type of material of the conductor and its temperature.

Say, the specific resistance of the material of a conductor = ρ

Therefore, the conductivity of its material is, σ = 1/ρ

As unit of ρ is Ω m, Therefore, the unit of σ is (Ω m)-1.


Example: The specific resistance of the nichrome wire used in an electrical heater is 100 x 10-8 Ω m. What will be the resistance of 15 m long wire having cross sectional area 2.0 x 10-7 m2?


Specific resistance, ρ =100 x 10-8 Ωm

Cross sectional area, A = 2.0 x 10-7 m2

Length of the wire, L = 15 m

Resistance, R = ?

We know,

R = ρ (L/A)

[(100 x 10-8 Ωm) * (15 m)] / (2.0 x 10-7 m2)

= 75 Ω (Ans)