Two magnets are held together in a vibration magnetometer and are allowed to oscillate in the earth’s magnetic field. With like poles of magnets together, $12\, oscillations$ per minute are made but for unlike poles together only $4\, oscillations$ per minute are executed. The ratio of their magnetic moments is

A short bar magnet placed in a horizontal plane has its axis aligned along the magnetic north-south direction. Null points are found on the axis of the magnet at $14\; cm$ from the centre of the magnet. The earth's magnetic field at the place is $0.36\; G$ and the angle of $dip$ is zero. What is the total magnetic field (in $G$) on the normal bisector of the magnet at the same distance as the null-point (i.e., $14 \;cm$) from the centre of the magnet? (At null points, field due to a magnet is equal and opposite to the horizontal component of earth's magnetic field.)

Tangent galvanometer is used to measure

$A $ magnet freely suspended in a vibration magnetometer makes $10 $ oscillations per minute at a place $A$  and $20 $ oscillations per minute at a place $B$. If the horizontal component of earth’s magnetic field at $A$ is $36 \times {10^{ - 6}}\,T$, then its value at $B$ is

Assertion : Magnetic Resonance Imaging $(MRI)$ is a useful diagnostic tool for producing images of various parts of human body.

Reason : Protons of various tissues of the human body play a role in $(MRI)$.

The magnetic needle of a tangent galvanometer is deflected at an angle $30^o$ due to a magnet. The horizontal component of the earth's magnetic field is $0.34 \times 10^{-4}\, T$ which is along the plane of the coil. The magnetic field due to magnet is