What is the most effective method of demagnetising a bar magnet?
Placing the magnet in a solenoid carrying a large a.c and gradually decreasing the current
Placing the magnet in a solenoid carrying a large d.c and gradually decreasing the current
Placing the magnet in a solenoid that produces a magnetic field in the opposite direction to the magnet
Placing the magnet next to an identical bar magnet with its poles in the opposite direction
