A semicircular arc of radius $r$ and a straight wire along the diameter, both are carrying same current $i$. Find out magnetic force per unit length on the small element $P$, which is at the centre of curvature.

• Correct answer
  A

  $\left(\frac{\mu_0 i^2}{4 r}\right)$
• B

  $\left(\frac{\mu_0 i^2}{2 r}\right)$
• C

  $\left(\frac{\mu_0 i^2}{r}\right)$
• D

  $\left(\frac{2 \mu_0 i^2}{r}\right)$

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