$A$ toroid has a non-ferromagnetic core of inner radius $r_{1}$ and outer radius $r_{2}$,around which $N$ turns of wire are wound. If the current in the wire is $I$,then the magnetic field inside the toroid is ($\mu_{0} =$ permeability of free space).

• A
  $\frac{\mu_{0} NI}{\pi(r_{1}+r_{2})}$
• B
  $\frac{\mu_{0} NI}{(r_{2}-r_{1})}$
• C
  $\frac{\mu_{0} NI}{(r_{1}+r_{2})}$
• D
  $\frac{\mu_{0} NI}{\pi(r_{2}-r_{1})}$