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A copper wire of radius 1 mm contains $10^{22}$ free electrons per cubic metre. The drift velocity for free electrons when 10 A current flows through the wire will be (Given, charge on electron = $1.6\times10^{-19}$ C):
A
$\dfrac{6.25\times10^4}{\pi}\ ms^{-1}$
B
$\dfrac{6.25}{\pi}\times10^3\ ms^{-1}$
C
$\dfrac{6.25}{\pi}\ ms^{-1}$
D
$\dfrac{6.25\times10^5}{\pi}\ ms^{-1}$
Detailed Solution
$I=neAV_d\Rightarrow V_d=\dfrac{I}{neA}=\dfrac{10}{10^{22}\times1.6\times10^{-19}\times\pi\times10^{-6}}=\dfrac{6.25}{\pi}\times10^3\ m/sec$.