The resistance of a wire of uniform diameter $d$ and length $L$ is $R$. The resistance of another wire of the same material but diameter $2d$ and length $4L$ will be
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(b) $R \propto \frac{l}{A} \propto \frac{l}{{{d^2}}}$ $\Rightarrow $ $\frac{{{R_1}}}{{{R_2}}} = \frac{{{l_1}}}{{{l_2}}} \times \,{\left( {\frac{{{d_2}}}{{{d_1}}}} \right)^2} = \frac{L}{{4L}}\,{\left( {\frac{{2d}}{d}} \right)^2} = 1$
$\Rightarrow $ $R_2 = R_1 = R.$
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