(i) Define the term drift velocity .
(ii) On the basis of electron drift , derive an expression for resistivity of a conductor in terms of number density of free electrons and relaxation time. On what factors does resistivity of a coductor depend ?
(iii) Why alloys like constantan and manganin are used for making standard restores ?

Explanation

(i) Drift velocity is defined as the average velocity with which the free electron gets drifted f in the direction of external electric field applied.
(ii) See Q. 27 2012 Set-I O.D., [Page 153]
(iii) Low value of temperature coefficient and high specific resistance .