Electromagnetic Induction

Electromagnetic induction is the creation of an electrical voltage—or the potential difference—across a conductor within a changing magnetic field. When a conductor cuts across a magnetic field, current flows in the conductor. It flows one way when the conductor cuts the field in one direction, then reverses as it cuts the field in the opposite direction. Thus, it creates alternating current, or AC.

FIGURE 36-19
Electromagnetic induction using a magnet rotating inside an iron yoke and winding.

Moving a wire inside a magnetic field produces a current flow. Similarly, moving a magnet inside a stationary coil of wire produces the same effect. For example, to generate electricity, a magnet can be rotated inside an iron yoke with a coil of wire wound around the stem of the yoke to form a complete circuit with an ammeter, which indicates current flow Figure 36-19. As the magnet rotates, the ammeter deflects for current flow. For every half-revolution, current flow reverses. Increasing the speed of the magnet increases the amount of electrical energy produced. Electromagnetic induction is applied in alternators, ignition coils, and some sensors on the vehicle.

To have induction, you have to have three things: a winding, a magnet, and relative movement (i.e., movement of one past the other). The amount of induction is dependent upon the strength of the magnetic field, the number of windings, the speed of the movement, and the relative distance between the field and the winding.

AS-75: Electromagnetism: The technician can explain the relationship between current in a conductor and strength of the magnetic field.

Faraday’s law of induction describes the ways that a voltage can be generated within a conductor moved through a magnetic field. Simply stated, whenever there is a change in the number of magnetic field lines passing through a conductor, whether the conductor is moved or changes occur in the magnetic field, a voltage is generated in the conductor. When the strength of the magnetic field is increased, there is an increase in the number of magnetic field lines. If we have a conductor moving through the magnetic field and the rate of movement remains constant, the increased intensity of the magnetic field will result in more magnetic field lines passing through the conductor, increasing the voltage generated.