Q. A very small magnet is placed in the magnetic meridian with its south pole pointing north. The null point is obtained $20\ cm$ away from the centre of the magnet. If the earth’s magnetic field (horizontal component) at this point is $0.3\ gauss$, the magnetic moment of the magnet is
A) $8.0 \times 10^{2}e.m.u$
B) $1.2 \times 10^{3}e.m.u$
C) $2.4 \times 10^{3}e.m.u$
D) $3.6 \times 10^{3}e.m.u$
Explanation
(b) At neutral point
$|B| = \left| B_{H} \right| \Rightarrow \frac{2M}{(20)^{3}} = 0.3 \Rightarrow M = 1.2 \times 10^{3}\ emu$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.