JAMB - Physics (1989 - No. 25)
A bar magnet is most effectively demagnetized by
placing it in a N - S position and hitting it with a hammer
subjecting it to an electric current from a battery
bringing its north pole in contact with the north pole of a very strong magnet
heating the magnet
ব্যাখ্যা
the most effective way of demagnetizing a magnet is Electrical method. option c is not correct since battery instead of a solenoid . option A is another method but the placing of the magnet is wrong it should of have been in the east-west direction not north-south direction. option C is not a method. so that leaves us with OPTION d which is also a method of demagnetizing a method, so when a magnets are strongly heated they lose their magnetism. therefore OPTION D is correct.