$A$ solenoid has a core of a material with relative permeability of $400$. The solenoid windings are insulated from the core and carry a current of $2 \text{ A}$. If the number of turns is $1000$ per meter,then the value of magnetic intensity will be . . . . . . .

• A
  $8 \times 10^5 \text{ A m}^{-1}$
• B
  $2 \times 10^3 \text{ A m}^{-1}$
• C
  $2 \times 10^{-3} \text{ A m}^{-1}$
• D
  $8 \times 10^{-5} \text{ A m}^{-1}$