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# The number of density of free electron in a copper conductor estimated at $8.5 \times 10^{20}m^{-3}$. How long does an electron take a drift from one end of a wire $3.0 \; m$ long to its other end ? The area of cross - section of the wire is $2 \times 10^{-6}\;m^2$ and it is carrying of $3.0 \;A$

$\begin{array}{1 1} 7\;hours\;and\;33\;minutes \\ 6\;hours\;and\;33\;minutes \\ 8\;hours\;and\;30\;minutes \\ 5\;hours\;and\;30\;minutes \end{array}$