The number density of free electrons in a copper conductor is `8.5 xx 10^28 m^(-3)` . How long does an electron take to drift from one end of a wire 3.0 m long to its other end ? The area of cross section of the wire is `2.0 xx 10^(-6) m^2` and is carrying a current of 3.0 A.

Explanation

Here `n = 8.5 xx 10^28 m^(-3), A=2.0 xx 10^(-6) m^2, I = 3.0 A `and l = 3.0 m
`because` Drift speed of electron `v_d = (I)/(nAe)`, hence time taken by an electron to drift through the entire length of wire is given as:
`t = (l)/(v_d) = (ln Ae)/(I) = (3.0 xx 8.5 xx 10^28 xx 2.0 xx 10^(-6) xx 1.6 xx 10^(-19) )/(3.0) = 2.7 xx 10^4 s `