Which method is the most effective for demagnetising a bar magnet?
- Aplacing the magnet in a solenoid carrying a large alternating current and gradually decreasing the current
- Bplacing the magnet in a solenoid carrying a large direct current and gradually decreasing the current
- Cplacing the magnet in a solenoid that produces a magnetic field in the opposite direction to the magnet
- Dplacing the magnet next to an identical bar magnet with its poles in the opposite direction