A bar magnet of magnetic moment \( 5.0\,\mathrm{A\,m^2} \) has poles \( 20\,\mathrm{cm} \) apart. The pole strength would be
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( 25\,\mathrm{A\,m} \)
The magnetic moment of a bar magnet is the pole strength times the magnetic length, which is the distance between the poles, \( 2l \).
\( \displaystyle M = m \times 2l \;\Rightarrow\; m = \frac{M}{2l} \)
\( \displaystyle 2l = 20\,\mathrm{cm} = 0.20\,\mathrm{m} \)
\( \displaystyle m = \frac{5.0}{0.20} = 25\,\mathrm{A\,m} \)
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), but it is still in the CUET 2026 syllabus, so do not skip it.
NCERT (Pre-rationalised edition, 2022-23):
Bar Magnet as an Equivalent Solenoid – “… Some textbooks assign a magnetic charge (also called pole strength) +qm to the north pole and –qm to the south pole of a bar magnet of length 2l, and magnetic moment qm(2l).”