Question

The number density of free electrons in a copper conductor is $8.5\times 10^{28}\cdot m^{-3}$. How long does an electron take to drift from one end of a wire $3.0m$ long to its other end? The area of crosssection of the wire is $2.0\times 10^{-6}{m}^2$ and it is carrying a current of $3.0A$.

• A. $8.1\times 10^{4}s$
• B. $2.7\times 10^{4}s$
• C. $9\times 10^{3}s$
• D. $3\times 10^{3}s$

Answer 1

Answer: (B)

Given, $l=3.0$
$A=2.0\times 10^{-6}{m}^2$
$i=30A$
$v_d=\frac{i}{neA}$
$v_d=\frac{3}{8.5\times 10^{28}\times 1.6\times 10^{-19}\times 2\times 10^{-6}}$
$v_d=1.10\times 10^{-4}$
Time $t=\frac{l}{v_d}$
$=\frac{3}{1.10\times 10^{-4}}$
$=2.7\times 10^{4}s$