Question

A copper wire of length $1\, m$ and uniform cross sectional area $5 \times 10^{-7} m ^{2}$ carries a current of $1\, A$. Assuming that there are $8 \times 10^{28}$ free electrons per $m ^{3}$ in copper, how long will an electron take to drift from one end of the wire to the other?

• A. $0.8 \times 10^{3} S$
• B. $1.6 \times 10^{3} S$
• C. $3.2 \times 10^{3} S$
• D. $6.4 \times 10^{3} S$

Answer 1

Answer: (D)

$t =\frac{l}{ v _{ d }}$
$I =neAv_d$
${ v _{ d }=\frac{ I }{ neA }}$
$t =\frac{l neA }{ I }$
$t =\frac{1 \times 8 \times 10^{28} \times 1.6 \times 10^{-19} \times 5 \times 10^{-7}}{1}$
$t =6.4 \times 10^{3} s$