When alternating current is passed through an $L-R$ series circuit,the power factor is $\frac{\sqrt{3}}{2}$ and $R=50 \ \Omega$. If the frequency of the source is $50 \ Hz$,then the value of $L$ is (Assume $\pi \approx 3.14$):
$\left[\cos \frac{\pi}{6}=\frac{\sqrt{3}}{2}, \quad \sin \frac{\pi}{6}=\frac{1}{2}, \quad \tan \frac{\pi}{6}=\frac{1}{\sqrt{3}}\right]$

• A
  $\frac{1}{2 \pi} \ H$
• B
  $\frac{\sqrt{3}}{2 \pi} \ H$
• C
  $\frac{1}{2 \sqrt{3} \pi} \ H$
• D
  $\frac{1}{\sqrt{3} \pi} \ H$