Magnetic Properties Of Materials

Two short bar magnets of length each have magnetic moments and respectively. They are placed on a horizontal table parallel to each other with their poles pointing towards the south. They have a common magnetic equator and are separated by a distance of . The value of the resultant horizontal magnetic induction at the mid-point of the line joining their centres is close to (Horizontal component of the earth's magnetic induction is

The B-H curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solenoid with 1000 turns/cm. The current that should be passed in the solenoid to demagnetise the ferromagnet completely is :

A compass needle of oscillation magnetometer oscillates 20 times per minute at a place P of dip 30°. The number of oscillations per minute become 10 at another place Q of 60° dip. The ratio of the total magnetic field at the two places (B_Q: B_P) is