A current I flows in an infinitely long wire with cross section in the form of a semicircular ring of radius R. The magnitude of the magnetic induction along its axis is

Question

( A ) $\frac{\mu_oI}{2 \pi R}$
( B ) $\frac{\mu_oI}{2 \pi^2 R}$
( C ) $\frac{\mu_oI}{4 \pi^2 R}$
( D ) $\frac{\mu_oI}{\pi^2R}$