Question

A hollow cylinder $(\rho =2.2\times {10}^{-8}\Omega m)$ of length 3 m has inner and outer diameter as 2 mm and 4 mm respectively. The resistance of the cylinder is

• A. $0.35\times {10}^{-3}\Omega$
• B. $3\times {10}^{-3}\Omega$
• C. $7\times {10}^{-3}\Omega$
• D. $2217\times {10}^{-3}\Omega$

Answer 1

The correct option is C $7\times {10}^{-3}\Omega$

$R=\frac{\rho l}{\pi (b^2-a^2)}=\frac{2.2\times {10}^{-8}\times 3}{\frac{22}{7}[2^2-1^2]{10}^{-6}}R=7\times {10}^{-3}\Omega$