Question

The resistance of a wire of length 300 m and cross-section area 1.0 mm² made of material of resistivity 1.0 × 10−7 Ωm is:

(a) 2 Ω
(b) 3 Ω
(c) 20 Ω
(d) 30 Ω

Answer 1

(d) 30 Ω

Resistance, $R=\frac{\mathrm{\rho }l}{A}$

Length, l = 300 m

Cross-section area, A = 1.0 mm² = 10^-6 m²

Resistivity, $\mathrm{\rho }$ = 1.0 × 10⁻⁷ Ωm

Resistance, $R=\frac{{10}^{-7}\times 300}{{10}^{-6}}$

R = 30 Ω