$A$ brass disc and a carbon disc of same radius are assembled alternatively to make a cylindrical conductor. The resistance of the cylinder is independent of the temperature. The ratio of thickness of the brass disc to that of the carbon disc is [$\alpha$ is temperature coefficient of resistance and Neglect linear expansion ]
Medium
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Given the resistance is independent of temperature.
Hence,
$\frac{\rho_{B} l_{B}}{A}\left(\alpha_{B} \Delta T\right)=\frac{\rho_{C} l_{C}}{A}\left(\alpha_{C} \Delta T\right)$
$\therefore \frac{l_{B}}{l_{C}}=\frac{\rho_{C} \alpha_{C}}{\rho_{B} \alpha_{B}}$
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