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.
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