There are 10²⁹ free electrons per cubic metre of copper. For a current of 16 A in a copper wire of 1 (mm)²  cross- section, the average speed of’ ’drift’ of the free electrons along the wire is

$10^{-3}m/s$

$ I = nv_d Ae $

$ \Rightarrow v_d = \frac{I}{nAe} = \frac{16}{ 10^{29} \times 10^{-6} \times 1.6\times 10^{-19}} = 10^{-3} m/s$