 KS3 Science Quiz - Electromagnets 01 (Questions)

This KS3 Science quiz takes a look at electromagnets. When electricity passes through a wire, it creates a weak magnetic field. If the wire is coiled into a spiral shape, the magnetic field from the wire is stronger. If the coil is wrapped round an iron core e.g. a nail, the magnetic field is made even stronger. But it doesn't stop there ... if you increase the current flowing through the coiled wire, the magnetic effect is also increased. Finally, if you add more coils to the spiral, the magnetism can be increased yet again! A coil of wire round an iron core that is connected to a source of electricity is called an electromagnet.

Electromagnets have two big advantages over permanent magnets - they can be switched on and off and they can be made to be very powerful. Three important uses are in electric motors, electric bells and relays.

A relay is a switch that is operated by electricity. It consists of a springy switch contact which is set up to be attracted by an electromagnet. When the electromagnet is switched on or off, the contact arm is attracted and the switch is operated. A relay is a good safety device as a low voltage circuit can be used to operate the electromagnet which then will operate the switch connected to a high voltage circuit. There is therefore no danger of the person operating the electromagnet coming into contact with the high voltage electricity.

1. The magnetic field around a straight wire carrying an electric current has:
 [ ] A circular shape [ ] A diamond shape [ ] A square shape [ ] An oval shape
2. 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
3. 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
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
5. 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
6. 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
7. Which of the following uses an electromagnetic effect?
 [ ] Iron [ ] Light bulb [ ] Toaster [ ] Washing machine
8. A relay uses a small current to:
 [ ] Attract a magnet [ ] Repel a magnet [ ] Switch off a current [ ] Switch on a larger current
9. A relay is used in:
 [ ] A car ignition [ ] An electric bell [ ] An electric cooker [ ] An iron
10. 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 KS3 Science Quiz - Electromagnets 01 (Answers)
1. The magnetic field around a straight wire carrying an electric current has:
 [x] A circular shape [ ] A diamond shape [ ] A square shape [ ] An oval shape
You may have seen this demonstrated at school using iron filings
2. The magnetic field around a coil of wire carrying current:
 [ ] Is a circular shape [ ] Is a diamond shape [ ] Is a square shape [x] Is the same shape as around a bar magnet
A coil of wire is known as a solenoid
3. If the current direction through the wire is reversed, the direction of the magnetic field:
 [x] 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
4. If the current in the wire increases, what happens to the strength of the magnetic field?
 [ ] It decreases [x] 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 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 [x] 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
6. Which of the following is a difference between an electromagnet and a permanent bar magnet?
 [ ] Electromagnets are stronger [x] Electromagnets can be turned off [ ] Permanent magnets are stronger [ ] Permanent magnets can be turned off
It is that feature that makes them so useful
7. Which of the following uses an electromagnetic effect?
 [ ] Iron [ ] Light bulb [ ] Toaster [x] Washing machine
Electromagnetic effect is used in any appliance with a motor
8. A relay uses a small current to:
 [ ] Attract a magnet [ ] Repel a magnet [ ] Switch off a current [x] 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
9. A relay is used in:
 [x] A car ignition [ ] An electric bell [ ] An electric cooker [ ] An iron
A starter motor needs a large current
10. An electromagnet on a crane is used in a scrapyard because:
 [x] 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