Question

A magnetic needle vibrates in a vertical plane parallel to the magnetic meridian about horizontal axis passing through its centre. The frequency is $\pi$. If the plane of oscillation turned about a vertical axis by ${90}^o$, the frequency of oscillation in vertical plane will be:

• A. $\pi$
• B. zero
• C. less than $\pi$
• D. more than $\pi$

Answer 1

Answer: (C)

less than $\pi$

Frequency $\pi =\frac{1}{2\pi }\sqrt{\frac{BM}{I}}$

On turning through angle $90°$, effective field is $V$ and $B>V$

$⟹$ new frequqncy $<\pi$ (less than $\pi )$