$A$ solenoid has a core of a material with relative permeability $400$. The windings of the solenoid are insulated from the core and carry a current of $1 \text{ A}$. If the number of turns is $1000 \text{ per metre}$,the magnetic field $(B)$ is . . . . . . $\text{T}$. (Given: $\mu_0 = 4\pi \times 10^{-7} \text{ SI units}$)

• A
  $1.6\pi \times 10^2$
• B
  $16\pi \times 10^2$
• C
  $16\pi \times 10^{-2}$
• D
  $0.16\pi \times 10^{-2}$