Magnetism And Matter

A bar magnet has a coercively . It is desired to demagnetize it by inserting it inside a solenoid long and having turns. The current carried by the solenoid should be:

A dip needle arranged to move freely in the magnetic meridian dips by an angle . If the vertical plane in which the needle moves is rotated through an angle to the magnetic meridian, then the needle will dip by an angle

If the total magnetic field due to earth is , then the total magnetic induction due to earth is