A 0.5 m long solenoid has 500 turns and has flux density of 2.52 × 10−3 T at its centre. The current in the solenoid is
(Given: μ0 = 4π × 10−7 Hm−1)
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 2.0 A
The field well inside a long solenoid is uniform and depends on the number of turns per unit length n, not on the total number of turns.
\( \displaystyle B = \mu_0 n I \)
\( \displaystyle n = \frac{N}{l} = \frac{500}{0.5\,\mathrm{m}} = 1000\,\mathrm{m^{-1}} \)
\( \displaystyle I = \frac{B}{\mu_0 n} \)
\( \displaystyle I = \frac{2.52\times10^{-3}\,\mathrm{T}}{4\pi\times10^{-7}\,\mathrm{H\,m^{-1}} \times 1000\,\mathrm{m^{-1}}} \)
\( \displaystyle I = \frac{2.52\times10^{-3}}{1.257\times10^{-3}}\,\mathrm{A} \)
\( \displaystyle I \approx 2.0\,\mathrm{A} \)
Note: A similar question was also asked in CUET (UG) 2026 on 24-05-2026 (Slot 2), and in CUET (UG) 2025 on 14-05-2025 (Slot 1).