Electromagnetic Effects of Electricity
FIGURE 36-22
Magnetic effects used in an electric motor.

Electricity can also create magnetic effects, referred to as electromagnetism. An electromagnet creates magnetic forces that attract both ferrous metals and unlike magnetic charges and that repel like magnetic charges. These forces can be used to create mechanical movement, such as in a relay or electric motor Figure 36-22. In electrical systems, magnetism occurs when a current passes through a conductor and a magnetic field is created around it. If the wire is wound into a coil, the magnetic fields combine to create a stronger and denser magnetic field, with a north and a south pole, just like a permanent magnet. Turn the current flow off, and the magnetic field collapses and disappears. By turning current to the coil on and off, this magnetic effect can be turned into a mechanical movement, pulling a switch open or closed. This is the principle behind a relay.

Reverse the current flow through the coil, and the north and south poles reverse.

Therefore, by passing electrical current through a coil, a magnetic field is produced, and turning it off causes the magnetic field to collapse. This is the operational theory behind an electromagnet. Electromagnets are constructed by winding a conductor wire, many hundreds or thousands of times, around a soft iron or metal core and passing a current through the coil. The strength of the magnetic field produced is determined by the number of turns, or coils, and the value of the current flow through the conductor. The metal core uniformly aligns the magnetic fields, which strengthens the magnetic effect. The size of the electromagnet is determined by its application. A fuel injector will contain a small electromagnetic coil using very fine wire, whereas a starter motor will use heavier wire in larger coils.

Many components use electromagnetism to operate. If a component has an electrical connection and movement is created by or within the component, then that component will use an electromagnet. Devices such as relays, solenoids, and motors use electromagnets to create movement. Ignition coils and transformers use electromagnetic induction to raise or lower voltage outputs. These devices will be examined further later in the chapter.

AS-63: Generators: The technician can explain how the movement of a conductor in a magnetic field will generate electricity.

When a conductor is moved through a magnetic field, an electrical current is generated within the conductor. This phenomenon is known as electromagnetic induction. Alternatively, the conductor can remain stationery while the magnetic field is moved in relation to it. The generation of a voltage depends directly on the movement of either the conductor or the magnetic field. Without movement there is no voltage generated.

Electromagnetic induction works by exposing the electrons within the conductor to a magnetic force acting perpendicular to both their motion and the magnetic field, which forces them to move through the conductor, creating a charge.