The magnetic field at the centre of a long solenoid having 400 turns per unit length and carrying a current ' $i$ ' is $6.24 \times 10^{-2} \mathrm{~T}$. The magnetic field at the centre of another long solenoid having 200 turns per unit length and carrying a current $\frac{' i^{\prime}}{2}$ is

• Correct answer
  A

  $1.56 \times 10^{-2} \mathrm{~T}$
• B

  $2.4 \times 10^{-2} \mathrm{~T}$
• C

  $26 \times 10^{-2} \mathrm{~T}$
• D

  $2.6 \times 10^{-2} \mathrm{~T}$

Hence, the correct answer is option: 'A'.