A wire carrying a current of $4A$  and its cross-sectional area${10}^{-8}{m}^2$ . If the free electron density in wire is${10}^{28}{m}^{-3}$ , the drift velocity is (in m/s)

current $i=4A$

cross-sectional area $A={10}^{-8}{m}^2$

number of electrons $n={10}^{28}{m}^{-3}$

charge $e=1.6\times {10}^{-19}$

drift velocity $V_d=?$

$V_d=\frac{i}{neA}$

      $=\frac{4}{{10}^{28}\times 1.6\times {10}^{-}{}^{19}\times {10}^{-8}}$

$\therefore V_d=0.25m/s$