Question

There is a current of $20\text{A}$ in a wire of cross-sectional area $0.01{\text{cm}}^2$. If number of free electrons per cubic metre is ${10}^{29}$, then the drift velocity will be

• A. $2.5\times {10}^{-3}{\text{ms}}^{-1}$
• B. $1.25\times {10}^3{\text{ms}}^{-1}$
• C. $1.25\times {10}^{-3}{\text{ms}}^{-1}$
• D. $2.5\times {10}^{-4}{\text{ms}}^{-1}$

Answer 1

The correct option is C $1.25\times {10}^{-3}{\text{ms}}^{-1}$

Since drift speed of electrons is,
$v_d=\frac{I}{neA}$

$=\frac{20}{{10}^{29}\times 1.6\times {10}^{-19}\times {10}^{-6}}$

$=12.5\times {10}^{-4}$

$=1.25\times {10}^{-3}{\text{ms}}^{-1}$