Several steel needles are suspended freely from hooks on a small brass disk, as shown in Fig.. If the pole of a strong magnet is slowly raised from below, the needles begin to separate, and then, when the magnet is quite close, they return to a vertical position. When the magnet is moved away, the needles again separate, forming a conical pencil. Discuss this behaviour of the needles.

A long rod made of soft iron is fixed in a vertical position. If a strong magnet A is brought into contact with its upper end, as shown in Fig., then the rod becomes so strongly magnetised that its lower end can support several small objects. If the same magnet is brought in contact with the side of the rod, quite close to the lower end (Fig,), then there is no such strong magnetisation, and the same objects cannot be supported at the lower end of the rod. Explain why magnet A acts differently in the two cases.

A compass needle free to turn in a horizontal plane is placed at the centre of circular coil of 30 turns and radius 12 cm. The coil is in a vertical plane making an angle of 45^@ with the magnetic meridian. When the current in the coil is 0.35 A, the needle points west to east. The current in the coil is reversed, and the coil is rotated about its vertical axis by an angle of 90^@ in the anticlockwise sense looking from above. Predict the direction of the needle. Take the magnetic declination at the places to be zero.

A compass needle free to turn in a horizontal plane is placed at the centre of a circular coil of 30 turns and radius 12 cm. The coil is in a vertical plane making an angle of 45^@ with the magnetic meridian when the current in the coil is 0.35amp., the needle points west to east. The current in the coil is reversed and the coil is rotated about its vertical axis by an angle of 90^@ in the anticlockwise sense looking from above. Predict the direction of the needle. Take the magnetic declination at the places to be zero.