Question

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

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

Answer 1

The correct option is C less than $\pi$

$n=\frac{1}{2\pi }\sqrt{\frac{MB}{I}}$
When it is turned by an angle ${90}^o$ the effective field is vertical $V$ and $B>V$
So, new frequency $<n$.