A magnetic needle is made to vibrate in uniform field $H$, then its time period is $T$. If it vibrates in the field of intensity $4H, $ its time period will be

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……$A$

The needle of a deflection galvanometer shows a deflection of $60^o $ due to a short bar magnet at a certain distance in $\tan A$ position. If the distance is doubled, the deflection is

In sum and difference method in vibration magnetometer, the time period is more if

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