Combination of Resistors: Practice Problem & Solution

Solution Explained:

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

Specific resistance depends only on the material, so it remains unchanged. Resistance $R = \rho \frac{l}{\pi r^{2}}$. If $l \rightarrow 2l$ and $r \rightarrow 2r$, $R' = \rho \frac{2l}{\pi (2r)^{2}} = \frac{1}{2} \rho \frac{l}{\pi r^{2}} = \frac{R}{2}$.