Magnetism_02B

A strong electromagnet is used to attract pins. What happens when the current in the coil is halved?

• No pins are attracted.

• Fewer pins are attracted.

• The same number of pins is attracted.

• Many more pins are attracted.

A solenoid carrying a current is used to demagnetise a bar magnet. Which conditions achieve demagnetisation?

• A

• B

• C

• D

A student wishes to demagnetise a steel bar. He uses the apparatus shown. Which type of electrical supply should the student use and what should he do with the steel bar?

• A

• B

• C

• D

An electromagnet is used to separate magnetic metals from non-magnetic metals. Why is steel unsuitable as the core of the electromagnet?

• It forms a permanent magnet.

• It has a high density.

• It has a high thermal capacity.

• It is a good conductor of electricity.

A piece of iron and a piece of steel are picked up by an electromagnet as shown. The current to the electromagnet is switched off. What happens?

• Both the iron and the steel remain magnetised.

• Neither the iron nor the steel remain magnetised.

• Only the iron remains magnetised.

• Only the steel remains magnetised.

Some electrical devices require a magnet which may be switched on and off many times in a

second. Which type of magnet may be used?

• an electromagnet only

• a permanent magnet only

• either a permanent magnet or an electromagnet

• neither a permanent magnet nor an electromagnet