Q. A bar-magnet of moment of inertia $49 \times 10^{- 2}\ kg - m^{2}$ vibrate in a magnetic field of induction $0.5 \times 10^{- 4}\ T.$ The time period of vibration is 8.8 s. The magnetic moment of the bar magnet is
A) $350\ A - m^{2}$
B) $490\ A - m^{2}$
C) $3300\ A - m^{2}$
D) $5000\ A - m^{2}$
Explanation
(d) Time period of magnet is
$\ \ \ \ \ \ \ \ T = 2\pi\sqrt{\frac{I}{MB_{H}}}$
Or $M = \frac{4\pi^{2}I}{T^{2}B_{H}}$
0r $M = \frac{4\ \times \ (3.14)^{2}\ \times \ 49\ \times \ 10^{- 2}}{(8.8)^{2}\ \times \ 0.5\ \times {\ 10}^{- 4}}$
$Or\ M = 5000\ A - m^{2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.