A half ring of radius R has charge $\mathrm{\lambda }$ per unit length. The potential at its centre is :

• A

  $\mathrm{k}\frac{\mathrm{\lambda }}{\mathrm{R}}$

• B

  $\mathrm{k}\frac{\mathrm{\lambda }}{\mathrm{\pi R}}$

• C

  $\frac{\mathrm{k\pi \lambda }}{\mathrm{R}}$

• D

  $\mathrm{k\pi \lambda }$