Question

A copper wire is stretched to make it $0.5 \%$ longer. The percentage change in its electrical resistance if its volume remains unchanged is:

• A. 2.50%
• B. 0.50%
• C. 1.00%
• D. 2.00%

Answer 1

Answer: (C)

1.00%

Answer 2

$R = \frac{\rho\ell}{A}$ and volume (V) = A$\ell$.

$R = \frac{\rho\ell^{2}}{V}$

$\Rightarrow \frac{\Delta R}{R} = \frac{2\Delta\ell}{\ell} = 1\%$

Therefore, The correct answer is option (C): 1.00%