Induction

As you can see, to induce electricity in a conductor, we must have a magnetic field and motion. In

automotive generators, mechanical energy from the engine is used to supply the motion. On some

types of generators, the conductor is moved through a stationary magnetic field, while on others the

magnetic field is moved and the conductor is stationary.

The induction principle is also used in TRANSFORMERS. A transformer is an electrical device

that is used for stepping up or stepping down electrical voltage. The ignition coil of an automotive

vehicle is actually a transformer that steps the 12- to 24-volt battery voltage up to the several

thousand volts needed to ignite the fuel mixture. In the following paragraphs, we will discuss the

construction and operation of transformers.

A simple transformer often contains an iron core and consists of two coils of wire. One coil is

actually an electromagnet and is called the primary winding. The second coil is called the

secondary winding.

If the primary winding is connected to a battery, current will flow through the winding causing a

magnetic field to build up around the coil. As the field builds up, its lines of force move outward

cutting across the coils of the secondary winding. The secondary winding will have a voltage

induced in it as a result of the lines of force cutting across its coils. Now, if the ends of the

secondary winding conductor were connected into a complete circuit, current would flow until the

induced voltage dropped to zero.

When the primary winding is disconnected from the battery, the magnetic lines of force will

collapse and disappear. As this happens, the lines of force move rapidly inward toward the primary

winding. Again, the moving lines of force cut across the coils of the secondary winding inducing a

voltage. This time the lines are moving in the opposite direction so the induced voltage causes

current to flow in the opposite direction.

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