Question

A metal wire of resistivity $64\times {10}^{-6}$ $\Omega$ and length $198$ $cm$ has a resistance of $7$ $\Omega$. Calculate its radius.

Answer 1

$R=\frac{\rho l}{A}$
$A=\frac{64\times {10}^{-6}\times 198\times {10}^{-2}}{7}$
$\Rightarrow A=1.810\times {10}^{(}-5)$ $m^2$
And $A=\pi r^2=1.810\times {10}^{-5}$
$\Rightarrow r=2.4$ $mm$