If a wire is stretched to make it $0.1 \%$ longer, its resistance will :
If a wire is stretched to make it $0.1 \%$ longer, its resistance will :
increase by $0.2 \%$
decrease by $0.2 \%$
decrease by $0.05 \%$
increases by $0.05 \%$
Solution
$\mathrm{R} \propto \ell^2$ (for a given volume)
$
\Rightarrow \frac{\Delta \mathrm{R}}{\mathrm{R}} \%=\frac{2 \Delta \ell}{\ell} \%
$
Thus when wire is stretched by $0.1 \%$ resistance increases by $0.2 \%$