Electromagnets are like normal magnets, but with one major difference. Their magnetic strength is produced by electricity. Because of this, the electromagnet's strength can be increased or decreased by changing the amount of electric current that flows through the magnet. This ability to alter in strength makes electromagnets useful in a variety of electric devices.
Electromagnets are used in a large number of electronic devices, including electric bells, motors, generators and particle accelerators. In these devices, the electromagnet is used to attract movable electric parts. Magnetic locks, loudspeakers and magnetic recording devices such as tape recorders, VCRs and computer disks also utilise electromagnets, as do industrial magnets that are needed to move heavy masses of magnetic material. Propulsion systems using electromagnets are used to provide power for spacecrafts. In addition, electromagnets are an essential component of magnetic levitation systems. These systems use specialised superconducting electromagnets that are used in magnetic-resonance imaging devices (MRIs) and for energy storage.
The main reason why electromagnets are often more useful than normal magnets lies in the ability to start, stop and control the strength of the magnetic field. They tend to be more powerful than normal magnets, and because of their versatility, can be divided into two groups of usefulness: traction magnets and lifting or holding magnets. Traction magnets are used to exert a magnetic pull over a distance, while lifting and holding magnets need simply to remain in contact with magnetic material. Permanent magnets are not as useful as traction or lifting and holding magnets when compared to electromagnets.
An electromagnet is, essentially, a wire coiled around a core; this core can be anything, even air. The electromagnet's strength is related to what the core is made of (metallic cores will produce a stronger magnet), how many times the wire is coiled around the core, and how much of the core is covered with coils. To produce a magnetic field, the wire must be attached to a power source, such as a battery. As electricity runs through the wire, through the coils, and back to the battery, a magnetic field is produced. The voltage of the electricity running through the wire also affects the strength of the magnet. If the wire is disconnected from the power source, the magnetic field will vanish.
If an electromagnet is attached to a battery as a power source and the positive and negative terminals are reversed, the electric current will flow through the wire in the opposite direction, causing the magnetic poles of the magnet to reverse. The electromagnet will then begin repelling items that it had been attracting. Many devices that use electromagnets take advantage of this principle, since it allows metal objects or other magnets to be repeatedly moved forwards and backwards by causing the electromagnet to attract and repel it in turn.
The use of electromagnetics has made many jobs easier and more efficient. For instance, in recycling plants, shredded garbage is dumped through magnetic fields generated by electromagnets in order to quickly sort out recyclable metal parts. Many laboratories use electromagnetic fields to sort particles in a particle beam out by mass. In the future, electromagnets promise to be of paramount importance in the widespread development and use of electric cars. Many scientists believe that further research with electromagnets could yield low pollution energy storage systems.