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(B) The resistance of a wire is given by $R = \rho \frac{\ell}{A}$.Since the volume $V = A \ell$ remains constant when the wire is stretched,we have $

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$0.2$

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(B) The resistance of a wire is given by $R = ho \frac{\ell}{A}$.Since the volume $V = A \ell$ remains constant when the wire is stretched,we have $A = \frac{V}{\ell}$.Substituting this into the resistance formula,we get $R = ho \frac{\ell^2}{V}$.Since $ho$ and $V$ are constant,$R \propto \ell^2$.Taking the derivative or using the approximation for small changes: $\frac{\Delta R}{R} \approx 2 \frac{\Delta \ell}{\ell}$.Given $\frac{\Delta \ell}{\ell} = 0.1\%$,the percentage change in resistance is $\frac{\Delta R}{R} 	imes 100 = 2 	imes 0.1\% = 0.2\%$.

$A$ copper wire is stretched to increase its length by $0.1\%$. What is the percentage increase in the resistance of the wire (in $\%$)?

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