When a wire of uniform cross section $a$, length $l$ and resistance $R$ is into a complete circle, resistance between any two of diametrically opposite point will be:

• Correct answer
  A

  $\frac{R}{4}$
• B

  $4 R$
• C

  $\frac{R}{8}$
• D

  $\frac{R}{2}$

Solution

Both are in parallel
$$ \begin{aligned} & \frac{1}{R^{\prime}}=\frac{2}{R}+\frac{2}{R}=\frac{4}{R} \\ & \Rightarrow \quad R^{\prime}=\frac{R}{4} \end{aligned} $$

Hence, the correct answer is option: 'A'.