magnetic field 2

Which statement about magnetism is correct?

• Aluminium is a ferrous metal.

• A steel magnet can be demagnetised by heating it.

• The core of an electromagnet is usually made of steel.

• The magnetic field lines around a bar magnet are evenly spaced.

An electromagnet is used to separate magnetic metals from non-magnetic metals.

Why is steel not suitable 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.

An old and expensive steel watch becomes magnetised.

The owner wants to use the watch again. He must demagnetise the watch.

What is the best method to do this?

• Heat it until it glows red hot.

• Pass direct current though it.

• Place it in a plastic bag and put the bag in hot water for several hours.

• Place it in a solenoid that carries alternating current and then slowly remove it.

A hard magnetic material can be used to make a permanent magnet.

A soft magnetic material can be used to make a temporary magnet.

Which row shows whether iron and steel are hard or soft magnetic materials?

• A

• B

• C

• D

How can a permanent magnet be demagnetised?

• cool the magnet for a long time

• hit the magnet repeatedly with a hammer

• leave the magnet in a coil which is connected to a battery

• shine bright light onto the magnet

In which pair are both metals ferrous?

• aluminium and copper

• aluminium and steel

• copper and iron

• iron and steel

Which statement describes a property of a magnet?

• It attracts ferrous materials.

• It could have only one pole (north or south).

• It points in a random direction when suspended.

• It repels non-ferrous materials.

Which procedure may be used to demagnetise a steel bar?

• cooling it in a freezer

• earthing it with a copper wire

• placing it in a solenoid carrying a large direct current (d.c.)

• striking it repeatedly with a hammer

The diagram shows a magnet being brought near to an unmagnetised iron bar. This causes the

iron bar to become magnetised.

• A

• B

• C

• D

A student wishes to make a permanent magnet. She has an iron rod and a steel rod.

Which rod should she use to make the permanent magnet, and is this rod a hard magnetic

material or a soft magnetic material?

• A

• B

• C

• D