There is a solenoid of length 1 m has a radius of 1 cm and is made up of 1000 turns. It carries a current of 10 A. The magnitude of magnetic field inside the solenoid is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( 4\pi \times 10^{-3}\,\mathrm{T} \)
The field inside a long solenoid is uniform and is given by \( B = \mu_0 n I \), where \( n \) is the number of turns per unit length. The length (1 m) is a hundred times the radius (1 cm), so the long-solenoid result applies; the radius does not enter the formula.
\( \displaystyle n = \frac{N}{L} = \frac{1000}{1\,\mathrm{m}} = 1000\,\mathrm{m^{-1}} \)
\( \displaystyle B = \mu_0 n I = 4\pi\times10^{-7}\,\mathrm{T\,m\,A^{-1}} \times 1000\,\mathrm{m^{-1}} \times 10\,\mathrm{A} \)
\( B = 4\pi\times10^{-3}\,\mathrm{T} \)
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 – …
