Consider a conductor XY of length L and area of cross section A (Fig ). An electric field E is applied between its ends. Let n be the number of free electrons per unit volume. The free electrons move towards the left with a constant drift velocity vd.
The number of conduction electrons in the conductor = nAL
The charge of an electron = e
The total charge passing through the conductor q = (nAL) e
The time in which the charges pass through the conductor, t = L/vd The current flowing through the conductor,
The current flowing through a conductor is directly proportional to the drift velocity. From equation (1),
Hence
