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

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 time period of a vibration magnetometer is $T_0$. Its magnet is replaced by another magnet whose moment of inertia is $3$ times and magnetic moment is $1/3$ of the initial magnet. The time period now will be

The time period of oscillation of a magnet in a vibration magnetometer is $1.5$ seconds. The time period of oscillation of another magnet similar in size, shape and mass but having one-fourth magnetic moment than that of first magnet, oscillating at same place will be.....$sec$

The error in measuring the current with a tangent galvanometer is minimum when the deflection is about.....$^o$

A tangent galvanometer has a coil of $25$ $turns$ and a radius of $15\, cm$. The horizontal component of the earth’s magnetic field is $3\times10^{-5}\, T$. The current required to produce a deflection of $45^o$ in it is....$A$