Q. A magnetic needle is made to vibrate in uniform field $H$, then it time period is $T$. If it vibrates in the field of intensity $4H$, its time period will be
A) $2T$
B) $T/2$
C) $2/T$
D) $T$
Explanation
(b) $T = 2\pi\sqrt{\frac{I}{MB_{H}}} \Rightarrow \frac{T_{1}}{T_{2}} = \sqrt{\frac{\left( B_{H} \right)_{2}}{\left( B_{H} \right)_{1}}}$
$\Rightarrow T_{2} = T\sqrt{\frac{(BH)_{1}}{(BH)_{2}}} = \frac{T}{2}\ \lbrack\because\left( B_{H} \right)_{2} = 4\left( B_{H} \right)_{1}\rbrack$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.