Resource 5: Electromagnets: Teacher notes
Background information / subject knowledge for teacher
A magnetic field is produced when an electric current flows through a coil of wire. This is the basis of the electromagnet. We can make an electromagnet stronger by:
- wrapping the coil around an iron core;
- adding more turns to the coil;
- increasing the current flowing through the coil.
The magnetic field around an electromagnet is just the same as the one around a bar magnet. It can, however, be reversed by turning the battery around. Unlike bar magnets, which are permanent, the magnetism of electromagnets can be turned on and off just by closing or opening the switch.
Many objects around you contain electromagnets. They are found in electric motors and loudspeakers. Very large and powerful electromagnets are used as lifting magnets in scrapyards to pick up, then drop, old cars and other scrap iron and steel.
Electric bells also contain an electromagnet.
- When the current flows through the circuit, the electromagnet makes a magnetic field.
- The electromagnet attracts the springy metal arm.
- The arm hits the gong, which makes a sound and the circuit is broken.
- The electromagnet is turned off and the springy metal arm moves back.
- The circuit is complete again.
- The cycle repeats as long as the switch is closed.
Original source:(Accessed 2008)