A solenoid has 100 turns and is of length 20 cm. It carries a current of 5A. The magnetic field in the middle of the solenoid is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 3.14 mT
Inside a long solenoid, away from its ends, the field is uniform and equals \( B = \mu_0 nI \), where \( n \) is the number of turns per unit length.
\( \displaystyle n = \frac{N}{l} = \frac{100}{0.20\,\mathrm{m}} = 500\,\mathrm{m^{-1}} \)
\( B = 4\pi\times10^{-7}\times500\times5\,\mathrm{T} = 3.14\times10^{-3}\,\mathrm{T} = 3.14\,\mathrm{mT} \)