A long vertical wire in which a current is flowing produces a neutral point with the earth's magnetic field at a distance of $5\, cm$ from the wire. If the horizontal component of the earth's magnetic induction is $0.18\, gauss$, then the curent in the wire is......$A$

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....$A$

Before using the tangent galvanometer, its coil is set in

In a vibration magnetometer, the time period of a bar magnet oscillating in horizontal component of earth's magnetic field is $2$ $sec$. When a magnet is brought near and parallel to it, the time period reduces to $1 $ $sec$. The ratio $H/F $ of the horizontal component $H$  and the field $F$ due to magnet will be

The length of a magnet is large compared to its width and breadth. The time period of its oscillation in a vibration magnetometer is $2 \,s. $ The magnet is cut along its length into three equal parts and three parts are then placed on each other with their like poles together. The time period of this combination will be

The ratio of magnetic moments of two bar magnet is $13 : 5$. These magnets are held together in a vibration magnetometer are allowed to oscillate in earth’s magnetic field with like poles together $15$ oscillation per minute are made. What will be the frequency of oscillation of system if unlike poles are together....$oscillations/min$