Q. The time period of a thin bar magnet in earth’s magnetic field is $T$. If the magnet is cut into equal parts perpendicular to its length, the time period of each part in the same field will be
A) $T/2$
B) $T/4$
C) $\sqrt{2}\ T$
D) $2\ T$
Explanation
(b) Mass becomes $1/$4 and length becomes $1/$4.
$\therefore$ Moment of inertia $I$ bocomes $\frac{1}{4}\left( \frac{1}{4} \right)^{2} = \frac{1}{64},$ Magnetic moment $M$ becomes $1/4$th.
As $T = 2\pi\sqrt{\frac{1}{MH},\ }\therefore T\ $becomes $1/4$th.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.