Q 12-04-241NEETNEET 2022Top questionEasy
A long solenoid of radius $1$ mm has $100$ turns per mm. If $1$ A current flows in the solenoid, the magnetic field strength at the centre of the solenoid is
Answer: (C) $12.56 \times 10^{-2}$ T
Turns per metre: $n = 100$ per mm $= 10^5\ \text{m}^{-1}$. The radius does not matter for a long solenoid.
$$B = \mu_0 nI = 4\pi \times 10^{-7} \times 10^5 \times 1 = 4\pi \times 10^{-2} \approx 12.56 \times 10^{-2}\ \text{T}$$
Solution by Sreeraj P, M.Sc Physics