A copper wire of diameter 1.02 mm carries a current of 1.7 amp.  Find the drift velocity (v_d) of electrons in the wire. 

            Given n, number density of electrons in copper  = 8.5 x 10²⁸ /m³.

1.5 mm/sec

I = 1.7 A
$ J =\text{ current density }= \frac{I}{\pi r^2} = \frac{1.7}{3.14\times (0.51\times 10^{-3})^2} = nv_d e = 8.5\times 10^{28} \times v_d \times 1.6\times 10^{-19}$

$ v_d = 1.5 mm/sec$