A bar magnet may be demagnetised either by striking it repeatedly over a long period or by gradually withdrawing it from a coil linked to a power supply. Which row correctly completes the descriptions of how these methods are performed?
- Ahammering bar magnet for a long time with magnet aligned E-W; slowly removing bar magnet from a coil connected to a d.c. power supply
- Bhammering bar magnet for a long time with magnet aligned E-W; slowly removing bar magnet from a coil connected to an a.c. power supply
- Chammering bar magnet for a long time with magnet aligned N-S; slowly removing bar magnet from a coil connected to a d.c. power supply
- Dhammering bar magnet for a long time with magnet aligned N-S; slowly removing bar magnet from a coil connected to an a.c. power supply