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A copper wire is stretched so that its length increases by 0.1%, with its volume essentially unchanged. What is the approximate percentage change in its electrical resistance?

1. 0.2 %
2. 0.1 %
3. 0.4 %
4. 0.8 %

Correct answer: 0.2 %

Solution

With volume constant, R is proportional to L², so a 0.1% increase in length gives a 2 x 0.1% = 0.2% increase in resistance.

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