Question:
A current of $10 \mathrm{~A}$ exists in a wire of crosssectional area of $5 \mathrm{~mm}^{2}$ with a drift velocity of $2 \times 10^{-3} \mathrm{~ms}^{-1}$. The number of free electrons in each cubic meter of the wire is
Correct Option: , 2
Solution:
$\mathrm{i}=10 \mathrm{~A}, \mathrm{~A}=5 \mathrm{~mm}^{2}=5 \times 10^{-6} \mathrm{~m}^{2}$
and $v_{d}=2 \times 10^{-3} \mathrm{~m} / \mathrm{s}$
We know, $\quad \mathrm{i}=$ neAvd
$\therefore 10=\mathrm{n} \times 1.6 \times 10^{-19} \times 5 \times 10^{-6} \times 2 \times 10^{-3}$
$\Rightarrow \mathrm{n}=0.625 \times 10^{28}=625 \times 10^{25}$