IGCSE Physics Paper-1: Specimen Questions with Answers 108 - 109 of 109

Question number: 108

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Question

An electromagnet is used to separate magnetic metals from no-magnetic metals. Why is steel unsuitable as the core of the electromagnet?

Choices

Choice (4) Response

a.

It has a high thermal capacity

b.

It forms a permanent magnet

c.

It is good conductor of electricity

d.

It has a high density

Answer

b.

Explanation

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

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Question

How can a permanent magnet be demagnetized?

Choices

Choice (4) Response

a.

cool the magnet for a long time

b.

heat the magnet

c.

pass a small current through the magnet

d.

leave the magnet in a coil which carries direct current

Answer

b.

Explanation

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.