Drift speed of electrons, when 1.5 A of current flows in a copper wire of cross section $5 \mathrm{~mm}_2$, is v . If the electron density in copper is $9 \times 10^{28} / \mathrm{m}^3$ the value of v in $\mathrm{mm} / \mathrm{s}$ is close to (Take charge of electron to be $=1.6 \times 10^{-19} \mathrm{C}$ )