Question

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

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

Answer 1

The correct option is C 0.024 cm

Resistance $R=\frac{\rho l}{\pi r^2}$
or $r^2=\frac{\rho l}{\pi R}=\frac{64\times {10}^{-6}\times {10}^{-2}\times 1.98}{3.14\times 7}=0.00024m=0.024cm$