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What is the difference between an electromagnet and a permanent bar magnet?

# Electromagnets 01

## An enjoyable way to test your knowledge about electromagnets. What's the purpose of a relay?

### Scroll down to play the quiz

1.
If the current direction through the wire is reversed, the direction of the magnetic field:
Is also reversed
Stays in the same direction
The current stops flowing
There is no magnetic field
Whenever there is a current flowing, an electromagnet will have a magnetic field around it
2.
The magnetic field around a straight wire carrying an electric current has:
A circular shape
A diamond shape
A square shape
An oval shape
You may have seen this demonstrated at school using iron filings
3.
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
It is that feature that makes them so useful
4.
If the current in the wire increases, what happens to the strength of the magnetic field?
It decreases
It increases
It stops the magnetic field
No change
There is a direct positive correlation between current and magnetic field strength
5.
Which of the following uses an electromagnetic effect?
Iron
Light bulb
Toaster
Washing machine
Electromagnetic effect is used in any appliance with a motor
6.
An electromagnet on a crane is used in a scrapyard because:
It can be turned on and off
It can't be turned on and off
It is stronger than a permanent magnet
It is weaker than a permanent magnet
They can also be made a lot stronger and for less cost than a permanent magnet of the same strength
7.
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
Making the coil wider will increase the strength
Putting an iron core into the coil will increase the strength
Making the coil wider would make it shorter, unless you used more wire
8.
A relay is used in:
A car ignition
An electric bell
An electric cooker
An iron
A starter motor needs a large current
9.
A relay uses a small current to:
Attract a magnet
Repel a magnet
Switch off a current
Switch on a larger current
When you press a lift button, it operates a relay that switches on the motor. The motor needs a high current and if that sort of current passed through a lift call button, it would be dangerous if something went wrong
10.
The magnetic field around a coil of wire carrying current:
Is a circular shape
Is a diamond shape
Is a square shape
Is the same shape as around a bar magnet
A coil of wire is known as a solenoid