Question

If a copper wire is stretched to make it 0.1% longer, then the percentage change in resistance is approximately –

• A. 0.1%
• B. 0.2%
• C. 0.4%
• D. 0.8%

Answer 1

Answer: (B)

0.2%

Answer 2

R =$\frac{\rho\mathcal{l}}{A}$ , m = A l d

\ R =$\frac{\rho\mathcal{l}(\mathcal{l}d)}{m}$ \ R µ l²

\ $\frac{\Delta R}{R}$ × 100 = 2 $\frac{\Delta\mathcal{l}}{\mathcal{l}}$× 100 = 2 × 0.1 = 0.2%