Current $i$ is passed through a circular arc as shown in the diagram. If the radius of the circle is $R$,then the magnetic flux density at the centre $P$ will be:

• A
  $\frac{{{\mu _0}i\alpha }}{{4\pi R}} \otimes $
• B
  $\frac{{{\mu _0}i(2\pi - \alpha )}}{{4\pi R}} \otimes $
• C
  $\frac{{{\mu _0}i\,\sin \,\alpha }}{{2\pi R}} \otimes $
• D
  $\frac{{{\mu _0}i\,\sin \,\alpha }}{{4\pi R}} \otimes $