The magnetic moment of a short bar magnet is \(8\,\mathrm{A\,m^{2}}\). The magnetic induction at a point on the axial line \(20\,\mathrm{cm}\) from its center is:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \(2\times10^{-4}\,\mathrm{T}\)
On the axial line of a short bar magnet, the field at distance r from its centre is
\( \displaystyle B = \frac{\mu_0}{4\pi}\frac{2M}{r^{3}} \)
\( \displaystyle r = 20\,\mathrm{cm} = 0.2\,\mathrm{m} \)
\( \displaystyle B = 10^{-7}\,\mathrm{T\,m\,A^{-1}} \times \frac{2 \times 8\,\mathrm{A\,m^{2}}}{(0.2\,\mathrm{m})^{3}} \)
\( \displaystyle B = 10^{-7} \times \frac{16}{8\times10^{-3}}\,\mathrm{T} \)
\( \displaystyle B = 2\times10^{-4}\,\mathrm{T} \)
Note: NTA picked this question from an NCERT (2026-27) exercise and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
