Q. Two identical bar magnets with a length $10\ cm$ and weight $50\ g$-$weight$ are arranged freely with their poles facing in a inverted vertical glass tube. The upper magnet hangs in the air above the lower one so that the distance between the nearest pole of the magnet is $3mm$. Pole strength of the poles of each magnet will be
A) $6.64\ amp \times m$
B) $2\ amp \times m$
C) $10.25\ amp \times m$
D) None of these
Explanation
(a) The weight of upper magnet should be balanced by the repulsion between the two magnets
$\therefore\frac{\mu_{0}}{4\pi}.\frac{m^{2}}{r^{2}} = 50\ gwt$
$\Rightarrow 10^{- 7} \times \frac{m^{2}}{(9 \times 10^{- 6})} = 50 \times 10^{- 3} \times 9.8$
$\Rightarrow m = - 6.64\ amp \times m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.