Question

A magnetic needle is kept in a uniform magnetic field of induction $0.5\times {10}^{-4}T$ . It makes $30$ oscillations per minute. If it is kept in a field of induction $2\times {10}^{-4}T$, then its frequency is :

• A. $1$ oscillation/s
• B. $60$ oscillations/s
• C. $15$ oscillations/min
• D. $1$ oscillations/s

Answer 1

Answer: (B)

$60$ oscillations/s

The time period of oscillation of a bar magnet freely suspended in air is given by
$T=2\pi \sqrt{\frac{I}{MB}}$
$\frac{f_2}{f_1}=\sqrt{\frac{B_2}{B_1}}$
$f_2=\sqrt{\frac{B_2}{B_1}}\times f_1$
$f_2=60$ oscillations /sec