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

Answer 1

Answer: (A)

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