I need help to solve the following question. The answer is B. Please help me to solve this question.
A bar magnet can be demagnetised by hammering it for a long time or by slowly removing it from a coil connected to a power supply.
Which row completes the descriptions of how these processes are carried out?
hammering bar magnet for a long time
A magnet aligned E-W slowly removing bar magnet from a coil connected to
a d.c. power supply
B magnet aligned E-W an a.c. power supply
C magnet aligned N-S a d.c. power supply
D magnet aligned N-S an a.c. power supply