question_answer

Length of a hollow tube is 5m, it?s outer diameter is 10 cm and thickness of it?s wall is 5 mm. If resistivity of the material of the tube is 1.7 ´ 10?8 W´m then resistance of tube will be

A)            5.6 ´ 10?5 W                          

B)            2 ´ 10?5 W

C)            4 ´ 10?5 W                              

D)            None of these

Correct Answer: A

Solution :

                   By using \[R=\rho .\frac{l}{A};\] here \[A=\pi (r_{2}^{2}-r_{1}^{2})\] Outer radius r2 = 5cm Inner radius r1 = 5 ? 0.5 = 4.5 cm So \[R=1.7\times {{10}^{-8}}\times \frac{5}{\pi \{{{(5\times {{10}^{-2}})}^{2}}-{{(4.5\times {{10}^{-2}})}^{2}}\}}\] \[=5.6\times {{10}^{-5}}\Omega \]