Question

To determine the magnitude of $B$ accurately, a small compass needle of known magnetic moment $m$ and moment of inertia $I$ is allowed to oscillate in the magnetic field. This arrangement is shown in figure.

The magnitude of the magnetic field if time period is $T$ is

• A. $B=\frac{4 \pi^{2} I}{m T^{2}}$
• B. $B=\frac{2 \pi^{2} I}{m T^{2}}$
• C. $B=\frac{\pi^{2} I}{2 m T^{2}}$
• D. $B=\frac{3 \pi^{2} I}{2 m T^{2}}$

Answer 1

Answer: (A)

The magnitude of the magnetic field is $B=\frac{4 \pi^{2} I}{m T^{2}}$.