IGCSE Physics Multiple Choice question

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Michaelbevan
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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
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Joinedup
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(Original post by Michaelbevan)
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
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Possibly you're just supposed to know and remember these 'magnet facts' for IGCSE but fwiw they are related to the domain theory of ferromagnetism.

the current in the demagnetising coil has to be alternating, Commercial 'degaussing' coils are available that work on this principle. so A and C are out

hammering a ferromagnet can reset the domains - tbh I think you'd end up with a weaker magnet and I'm not entirely sure it makes much difference which way it's oriented in the earths magnetic field.when you're hammering it.
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Ahser
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B as ac current will change continuously so the align domain also changes and E W are opp to N S so hammering at that direction would make it lose its magnetism
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