Q. Two bar magnets of the same mass, same length and breadth but having magnetic moments $M$ and 3M are joined together pole for pole and suspended by a string. The time period of assembly in a magnetic field of strength $H$ is 3 s. If now the polarity of one of the magnets is reversed and the combination is again made to oscillate in the same field, the time of oscillation is
A) 3 s
B) $3\sqrt{3}$ s
C) $3/\sqrt{3}$ s
D) 6 s
Explanation
(b) In pole for pole combination,
$M_{1} = 3M\ and\ M_{2} = M$
$T_{2} = ?$
$\frac{T_{2}}{T_{1}} = \sqrt{\frac{M_{1}}{M_{2}}} = \sqrt{\frac{3\ M}{M}} = \sqrt{3}$
$T_{2} = \sqrt{3}T_{1} = 3\sqrt{3}$ s
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.