Unit 9. 3 Electromagnets

Which of the following is a difference between an electromagnet and a permanent bar magnet?

• Electromagnets are stronger

• Electromagnets can be turned off

• Permanent magnets are stronger

• Permanent magnets can be turned off

An electromagnet on a crane is used in a scrapyard because:

• It is stronger than a permanent magnet

• It can't be turned on and off

• It is weaker than a permanent magnet

• It can be turned on and off

A relay uses a small current to:

• Repel a magnet

• Switch on a larger current

• Attract a magnet

• Switch off a current

Which of the following uses an electromagnetic effect?

• Iron

• Light bulb

• Toaster

• Washing machine

The magnetic field around a coil of wire carrying current:

• Is a circular shape

• Is a square shape

• Is the same shape as around a bar magnet

• Is a diamond shape

If the current in the wire increases, what happens to the strength of the magnetic field?

• It decreases

• No change

• It increases

• It stops the magnetic field

If the current direction through the wire is reversed, the direction of the magnetic field:

• There is no magnetic field

• The current stops flowing

• Stays in the same direction

• Is also reversed

A relay is used in:

• A car ignition

• An electric bell

• An electric cooker

• An iron

Which of the following is NOT true about the magnetic field around a coil of wire carrying a current?

• Changing the direction of the current will reverse the poles

• Increasing the number of coils will increase the strength

• Putting an iron core into the coil will increase the strength

• Making the coil wider will increase the strength

What happens to the magnetic field around a coil of wire carrying current if the number of coils is decreased?

• The strength of the magnetic field increases

• The strength of the magnetic field decreases

• The shape of the magnetic field changes

• The magnetic field disappears