Explain how the resistivity of a conductor depends upon relaxation time `tau`?

Resistance of a conductor depends on:

Explain how the resistivity of a conductor depends upon number density 'n' of free electrons?

Explain how does resistivity of a conductor depend upon number density n of free electron relaxation time tau ?

Stability of ecosystem depends upon

Define resistivity and state its SI unit. State and explain how to resitivity of a conductor varies with temperature.

Write the mathematical relation for the resistivity of a material in terms of relaxation time, number density, mass and charge carries in it. Explain using this relation, why the resistivity of a metal increases and that of semiconductor decreases with rise in temperature.