Question

As the temperature of a conductor increases, its resistivity and conductivity change. The ratio of resistivity to conductivity
(a) increases
(b) decreases
(c) remains constant
(d) may increase or decrease, depending on the actual temperature

Answer 1

(a) increases

Resistivity (ρ) of a conductor is the reciprocal of the its conductivity(σ). Thus,
$\rho =\frac{1}{\sigma }$
The ratio of the resistivity and the conductivity,

$\frac{\rho }{\sigma }=\frac{\rho }{1/\rho }={\rho }^2$
As resistivity increases with temperature, the square of resistivity will also increase. Hence, the ratio of resistivity and conductivity will increase with increase in temperature.