Question

Current is flowing with a current density $j=480Ac{m}^{-2}$ in a copper wire.
Assuming that each copper atom contributes one free electron and given that Avogadro number $=6.0\times 10^{23}atommo{l}^{-1}$
Density of copper $=9.0gc{m}^{-2}$
Electronic charge $=1.6\times 10^{-19}C$
Atomic weight of copper $=64gmo{l}^{-1}$
The drift velocity of electrons is

• A. $1mm{s}^{-1}$
• B. $2mm{s}^{-1}$
• C. $0.5mm{s}^{-1}$
• D. $0.36mm{s}^{-1}$

Answer 1

Answer: (D)

Drift velocity is given by
$v_d=\frac{I}{nqA}$
where I is current, n the number of electrons, A the area, q the charge.
Given $\frac{I}{A}=\frac{480A}{c{m}^2}andq=1.6\times 10^{-19}C$
$n=\frac{6\times 10^{23}\times 9}{64}$
$\therefore v_d=480\times \frac{64}{6\times 10^{23}\times 9\times 1.6\times 10^{-19}}$
$\Rightarrow v_d=\frac{480\times 64}{6\times 9\times 1.6\times 10000}cm{s}^{-19}$
$\Rightarrow v_d=\frac{32}{900}cm{s}^{-1}$
$=\frac{32\times 10}{900}cm{s}^{-1}$
$=0.36mm{s}^{-}1$
$\Rightarrow v_d=0.36mm{s}^{-}1$