Discussion
A wire is stretched to double its length. The percentage change in the resistance is
Answer: D
The resistance increases by 300%.
Stretching does not change the volume, so A × L stays constant: doubling the length halves the cross-section. With R = \(\rho L/A\):
\[ R' = \frac{\rho(2L)}{A/2} = 4R \]
The new resistance is four times the old, a change of (4R - R)/R = 300%. 100% comes from doubling the length but forgetting the thinner section, and 200% confuses 'four times' with 'increase of'.
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