A solenoid of length 0.5 m and radius 10 cm has 500 turns. If a current of 5 A flows through it, the magnetic field produced inside the solenoid will be:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( 6.28\times10^{-3}\,\mathrm{T} \)
The field inside a long solenoid is uniform and depends only on the number of turns per unit length and the current, \( B = \mu_0 n I \). The radius does not enter.
\( \displaystyle n = \frac{N}{l} = \frac{500}{0.5\,\mathrm{m}} = 1000\,\mathrm{m^{-1}} \)
\( \displaystyle B = \mu_0 n I = 4\pi\times10^{-7} \times 1000 \times 5 = 2\pi\times10^{-3}\,\mathrm{T} \)
\( \displaystyle B \approx 6.28\times10^{-3}\,\mathrm{T} \)
Note: NTA picked this question from an NCERT (2026-27) example and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
The Solenoid – …
