The number density of free electrons in copper is nearly \( 8 \times 10^{28} \, \text{m}^{-3} \). A copper wire has its area of cross section \( = 2 \times 10^{-6} \, \text{m}^2 \) and is carrying a current of \( 3.2 \, \text{A} \). A drift speed of the electrons is ______ \( \times 10^{-6} \, \text{ms}^{-1} \).