Electromagnets 01
What is the difference between an electromagnet and a permanent bar magnet?

Electromagnets 01

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.

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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.

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  1. An electromagnet on a crane is used in a scrapyard because:
    They can also be made a lot stronger and for less cost than a permanent magnet of the same strength
  2. If the current in the wire increases, what happens to the strength of the magnetic field?
    There is a direct positive correlation between current and magnetic field strength
  3. Which of the following is NOT true about the magnetic field around a coil of wire carrying a current?
    Making the coil wider would make it shorter, unless you used more wire
  4. A relay uses a small current to:
    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
  5. The magnetic field around a coil of wire carrying current:
    A coil of wire is known as a solenoid
  6. The magnetic field around a straight wire carrying an electric current has:
    You may have seen this demonstrated at school using iron filings
  7. If the current direction through the wire is reversed, the direction of the magnetic field:
    Whenever there is a current flowing, an electromagnet will have a magnetic field around it
  8. Which of the following uses an electromagnetic effect?
    Electromagnetic effect is used in any appliance with a motor
  9. Which of the following is a difference between an electromagnet and a permanent bar magnet?
    It is that feature that makes them so useful
  10. A relay is used in:
    A starter motor needs a large current

Author: Sue Davison

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