Equal potentials are applied on an iron and copper wire of same length. In order to have the same current flow in the two wires, the ratio $r$ (iron)/$r$ (copper) of their radii must be (Given that specific resistance of iron = $1.0 \times {10^{ - 7}}$ $ ohm-m$ and specific resistance of copper = $1.7 \times {10^{ - 8}}\,ohm-m$)
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(b) $\frac{{{r_{{\rm{iron}}}}}}{{{r_{{\rm{Copper}}}}}} = \sqrt {\frac{{{\rho _{{\rm{iron}}}}}}{{{\rho _{{\rm{copper}}}}}}} = \sqrt {\frac{{1 \times {{10}^{ - 7}}}}{{1.7 \times {{10}^{ - 8}}}}} \approx 2.4$.
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