Electromagnets--magnets powered by electricity--have become indispensable in modern life, incorporated into devices from motors to loudspeakers. An electromagnet consists of one or more coils of wire through which electrical current passes. Typical electromagnets contain many coils and a metal core that strengthens the magnetic field. Laboratory demonstration can reinforce concepts for Key Stage 3 students, those aged 11 to 14, as they learn about the various uses of electromagnets.
Ubiquitous in everyday tools and appliances---including almost everything with a fan or pump---electric motors are powered by electromagnets. One of the simplest motor designs incorporates an electromagnet, two permanent magnets on a shaft and a reed switch, which is a type of switch that responds to magnetic fields. The electromagnet pushes on the permanent magnets to cause the shaft to rotate. This type of motor uses direct current, or DC, so it can be powered by a battery. Building a motor from a kit is fun for KS3 students and gives them a hands-on way to explore how electromagnets can be used in motors.
Speakers produce or magnify sound by using electromagnets. Varying amounts of current pass through a coil of wire in a magnetic field. The interaction between the existing magnetic field and the electromagnet formed by the coil causes a diaphragm attached to the coil to vibrate, creating sound waves. Students can investigate this type of device by taking apart an old speaker and identifying its parts.
Magnetic storage media are still one of the most common types of data storage, even though video and audio cassettes, which use magnetic tape, are obsolete. Computer hard drives, flash drives and magnetic-stripe cards such as credit cards use magnetic data storage, made possible by electromagnets. A possible in-class demonstration could show how magnets destroy information stored on magnetic tape. This demonstration requires an old VCR or tape deck and a cassette. Show the students how the cassette plays before and after exposure to magnets of varying strengths. Explain that information is read and recorded by electromagnetic tape heads in the VCR or tape deck.
A galvanometer is a device that detects electrical currents using an electromagnet. An electric current passing through a wire produces a magnetic field, and galvanometers detect currents by reacting to the magnetic field they produce. While the instructor can use a commercial galvanometer as a demonstration, students can also use a compass to detect current through a wire. For this procedure, each student or group will need a compass, a length of copper wire--insulated by varnish, vinyl, etc.--and a small battery, such as a 9-volt. The wire must be wrapped across and then behind the compass face several times, then the assembly should be rotated so the compass needle is parallel to the wire loops. Students then attach the two ends of wire to the battery terminals, which will produce a current through the wire. The compass needle should react to the presence of the current by moving perpendicular to the wire loops.