CIE Physics Paper-1: Specimen Questions 108 - 109 of 109
Question number: 108
An electromagnet is used to separate magnetic metals from no-magnetic metals. Why is steel unsuitable as the core of the electromagnet?
It is good conductor of electricity
It has a high density
It has a high thermal capacity
It forms a permanent magnet
In electromagnet when we remove current the magnetic field should be removed. But if we take steel as the core of the electromagnet and starts the current the steel will magnetized and although current will off, the steel will be permanent magnet.
Question number: 109
How can a permanent magnet be demagnetized?
heat the magnet
leave the magnet in a coil which carries direct current
cool the magnet for a long time
pass a small current through the magnet
In permanent magnet alignment of the domain properly unidirectional. To demagnetize the permanent magnet these alignment of the domain should be random. So by heating the magnet domain arranged randomly and it is demagnetized.