Variation of Resistance with Temperature: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Variation of Resistance with Temperature. Understanding the underlying formula is key to arriving at the correct answer below:

In series connection, $R_{eq} = R_1 + R_2 \implies \frac{2l}{\sigma_{eq} A} = \frac{l}{\sigma_1 A} + \frac{l}{\sigma_2 A}$.
$\frac{2}{\sigma_{eq}} = \frac{\sigma_1 + \sigma_2}{\sigma_1 \sigma_2} \implies \sigma_{eq} = \frac{2\sigma_1 \sigma_2}{\sigma_1 + \sigma_2}$.