Question

A cylindrical conductor of length l and cross-section area A is connected to a DC source. Under the influence of an electric field set up due to the source, the free electrons begin to drift in the opposite direction of the electric field.

1. Draw the curve showing the dependency of drift velocity on relaxation time.
2. If the DC source is replaced by a source whose current changes its magnitude with time such that I = I₀ sin 2πvt, where v is the frequency of variation of current, then determine the average drift velocity of the free electrons over one complete cycle.

Answer 1

1. `"Drift velocity" ∝ 1/("Relaxation time")`
   
2. Alternating current changes direction every half cycle.
   So average drift velocity is zero.