Question

For a vibration magnetometer, the time period of a freely suspended bar magnet can be reduced by:

• A. Moving it towards south pole
• B. Moving it towards north pole
• C. Moving it towards equator
• D. None

Answer 1

Answer: (C)

Moving it towards equator

we know,
The time period of vibration magnetometer is,
$T=2\pi \sqrt{\frac{1}{mH}}$
For some moment of inertia $I$ and magnetic moment $m$
$T\propto \frac{1}{\sqrt{H}}$
T can be reduced if horizontal component of earth's magnetic field $H$ is increased. But
$H=R\cos \theta$
$H$ is high if the dip is zero.
This occurs at the equator.
Hence the period can be reduced by moving towards the equator.