Before using the tangent galvanometer, its coil is set in

In a tangent galvanometer a current of $0.1 \,A $ produces a deflection of $30^o$. The current required to produce a deflection of $60^o$ is……$A$

A vibration magnetometer placed in magnetic meridian has a small bar magnet. The magnet executes oscillations with a time period of $2\, sec$ in the earth's horizontal magnetic field of $24$ $microtesla$ . When a horizontal field of $18$ $microtesla$ is produced opposite to the earth's field by placing a current carrying wire, the new time period of magnet will be….$s$

The bob of a simple pendulum is replaced by a magnet. The oscillations are set along the length of the magnet. A copper coil is added so that one pole of the magnet passes in and out of the coil. The coil is short-circuited. Then which one of the following happens

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 $3$ $sec$ and at these places the earth's horizontal components are $H_A$ and $H_B$ respectively. Then the ratio between $H_A$ and $H_B$ will be