Question

A metal wire of specific resistance $ 64\times 10^{-6}\Omega\, cm $ and length $ 198\,cm $ has a resistance of $ 7\,\Omega $ . The radius of the wire will be

• A. 2.4 cm
• B. 0.24 cm
• C. 0.024 cm
• D. 24 cm

Answer 1

Answer: (C)

Specific resistance $\rho=\frac{R A}{l}$
$=\frac{R \pi r^{2}}{l}$
$\Rightarrow r^{2} =\frac{\rho l}{R \pi}$
$=\frac{64 \times 10^{-6} \times 198}{7 \times 3.14}$
$r =0.024\, cm$