Solution

A circular copper rod is $50\,\mathrm{cm}$ long and has $1\,\mathrm{cm}$ diameter. Find the resistance across its ends. What should be the side of square cross-section of a $50\,\mathrm{cm}$ long tungsten rod if its resistance is the same? [Resistivity of copper is $1.69 \times 10^{-8}\,\Omega\cdot\mathrm{m}$ and that of tungsten is $5.0 \times 10^{-8}\,\Omega\cdot\mathrm{m}$.]