Question

(a) Give two examples of substances which are good conductors of electricity. Why do you think they are good conductors of electricity ?
Calculate the resistance of a copper wire $1.0km$ long and $0.50mm$ diameter if the resistivity of copper is $1.7\times {10}^{-8}\Omega m.$

Answer 1

(a) Silver and copper are good conductors of electricity because they have free electrons available for conduction.

(b) $l=1km=1000m$
$r=\frac{d}{2}=\frac{0.5}{2}mm=0.25mm=0.25\times {10}^{-3}m$
$\rho =1.7\times {10}^{-8}\Omega m$

$R=\rho \frac{l}{A}=\rho \frac{l}{\pi r^2}$

$R=1.7\times {10}^{-8}\times \frac{1000}{3.14\times (0.25\times {10}^{-3}{)}^2}=86.6\Omega$