A current of $10\, A$ exists in a wire of crosssectional area of $5\, mm ^{2}$ with a drift velocity of $2 \times 10^{-3}\, ms ^{-1}$. The number of free electrons in each cubic meter of the wire is ..........
JEE MAIN 2021, Medium
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$i =10 A , A =5 mm ^{2}=5 \times 10^{-6} m ^{2}$
and $v _{ d }=2 \times 10^{-3} m / s$
We know, $i= neAvd$
$\therefore 10= n \times 1.6 \times 10^{-19} \times 5 \times 10^{-6} \times 2 \times 10^{-3}$
$\Rightarrow n =0.625 \times 10^{28}=625 \times 10^{25}$
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