Question

derive the expression for drift velocity

Answer 1

Derive an expression for current in terms of drift velocity. (Derive I = nAev)


Consider a conductor of length l and area of cross section A. Let the number of free electrons per unit volume be n. When a pd V is applied, let the drift velocity of electrons be v.

The total no. of free electrons in the piece of conductor = nAl (no. of free electrons per unit volume x volume)

Total charge due to free electrons; q  = nAle

The time taken by this charge to completely traverse the conductor, t =l/v

Therefore, the current in the conductor, I=q/t = nAle/(l/v) = nAev

i.e; I=nAev