$A$ current of $5 \ A$ flows through a toroid having a core of mean radius $20 \ cm$. If $4000$ turns of the conducting wire are wound on the core,then the magnetic field inside the core of the toroid is [permeability of free space $= 4 \pi \times 10^{-7} \ T \cdot m/A$]

• A
  $8 \times 10^{-2} \ Wb/m^2$
• B
  $6 \times 10^{-2} \ Wb/m^2$
• C
  $5 \times 10^{-2} \ Wb/m^2$
• D
  $2 \times 10^{-2} \ Wb/m^2$