Question

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^–8Ω×m then resistance of tube will be

• A. 5.6 × 10^–5Ω
• B. 2 × 10^–5Ω
• C. 4 × 10^–5Ω
• D. None of these

Answer 1

Answer: (A)

5.6 × 10^–5Ω

Answer 2

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

$\mathrm { R } = 1.7 \times 10 ^ { - 8 } \times \frac { 5 } { \pi \left\{ \left( 5 \times 10 ^ { - 2 } \right) ^ { 2 } - \left( 4.5 \times 10 ^ { - 2 } \right) ^ { 2 } \right\} } = 5.6 \times 10 ^ { - 5 } \Omega$