A copper wire is stretched to make it $0.5\%$ longer. The percentage change in its electric resistance if its volume remains unchanged is ................ $\%$
JEE MAIN 2019, Medium
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$ \mathrm{R} =\frac{\rho \ell}{\mathrm{A}} $
$ \mathrm{R} =\frac{\rho \ell^{2}}{\mathrm{A} \ell}=\frac{\rho \ell^{2}}{\mathrm{V}}$
$\frac{\mathrm{d} \mathrm{R}}{\mathrm{R}}=\frac{2 \mathrm{d} \ell}{\ell} $
${\rm{ Hence, }}\frac{{{\rm{dR}}}}{{\rm{R}}}{\rm{ }} = 1\% $
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