AIEEE 2002 Physics Solved Paper

Specific resistance is resistivity which is given by
ρ=‌

m

me2τ

where n=no. of free electrons per unit volume and τ= average relaxation time
For a conductor with rise in temperature n increases and τ decreases. But decrease in τ is more dominant than increase in n resulting an increase in the value of ρ
For a semiconductor with rise in temperature, n increases and τ decreases. But the increase in n is more dominant than decrease in τ resulting in decrease in the value of ρ.