The ratio of drift velocity to that of the thermal velocity of an electron in an conductor is -------------------------

In three dimension, the thermal velocity of electron, v_th = [3KT/m]^1/2

drift velocity of electron, v_d = eEτ/m

Thus,

At room temperature(300K), value of thermal velocity,v_th ∼ 10⁵m/s

For E = 100V/m and average relaxation time at room temperature 10^-13 s approx.

v_d = 2m/s approx.

ratio v_d / v_th = 2x 10^-5