MCQ
At two places $A$ and $B$ using vibration magnetometer, a magnet vibrates in a horizontal plane and its respective periodic time are $2$ sec and $3 \mathrm{sec}$ and at these places the earth's horizontal components are $H$ and $H$ respectively. Then the ratio between $H$ and $H$ will be
  • $9: 4$
  • B
    $3: 2$
  • C
    $4: 9$
  • D
    $2: 3$

Answer

Correct option: A.
$9: 4$
$T=2 \pi \sqrt{\frac{I}{M H}} \Rightarrow T \propto \frac{1}{\sqrt{H}} \Rightarrow \frac{T_A}{T_B}=\sqrt{\frac{H_B}{H_A}}$
$ \Rightarrow \frac{H_A}{H_B}=\left(\frac{T_B}{T_A}\right)^2=\left(\frac{3}{2}\right)^2=\frac{9}{4}$

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