A current of 2   A flows through a wire of cross-sectional area 25 . 0   mm 2 . The number of free…

The drift velocity is given by 

$v_d=\frac{I}{neA}$

$\Rightarrow I=nAe{v}_d ...\left(i\right)$

The given data is 

$$\begin{gathered} I=2 \mathrm{A} \\ \mathrm{A}=25\times {10}^{-6} {\mathrm{m}}^2 \\ \mathrm{n}=2\times {10}^{28} \\ \mathrm{e}=1.6\times {10}^{-19} \mathrm{C} \end{gathered}$$

Substituting the given values in equation (i)

$$\begin{gathered} 2=2\times {10}^{28}\times 25\times {10}^{-6}\times 1.6\times {10}^{-19}\times v_d \\ \Rightarrow v_d=\frac{2}{2\times {10}^{28}\times 25\times {10}^{-6}\times 1.6\times {10}^{-19}} \end{gathered}$$

$\Rightarrow v_d=\frac{1}{25\times 1.6\times 1000} \mathrm{m} {\mathrm{s}}^{-1}=25\times {10}^{-6} \mathrm{m} {\mathrm{s}}^{-1}$