Faraday’s Discovery

We already know that an electric current produces a magnetic field We already know that an electric current produces a magnetic field. Is the reverse true? Can a magnetic field produce an electric current? In 1831, Michael Faraday experimented with conductors in the vicinity of magnetic fields. From his experiments, he came up with a general statement…

Faraday’s Law of Electromagnetic Induction An electric current is induced in a conductor whenever the magnetic field in the region of the conductor changes amount or direction.

Mutual Induction Occurs whenever a changing current in one coil induces a current in a nearby coil The magnitude of an induced current in a coil is affected by: The number of turns on the induction coil The rate of change of the inducing magnetic field The strength of the inducing magnetic field

Direction of Induced Current

A few years after Faraday published his work, a physicist named Heinrich Lenz applied the law of conservation of energy to electromagnetic induction. Lenz came up with a rule to determine the direction of the induced current.

Lenz’s Law of Induced Current The direction of the induced current creates an induced magnetic field that opposes the motion of the inducing magnetic field.

Electric Generators: AC and DC

An electric generator is a device for converting mechanical energy into electrical energy by rotational motion. The rotational motion comes from a continuous source of energy, such as falling water, wind, or expanding steam.

The main components of a generator are magnets, an armature, brushes and either slip rings (for an AC generator) or a split-ring commutator (for a DC generator). A magnet attached to the end of a rotating shaft is positioned inside a stationary conducting ring that is wrapped with a continuous (and very long) piece of wire.

When the magnet rotates, it induces a small electric current in each section of wire as it passes. All the small currents of the individual sections add up to one larger current. This current is what is used for electric power.

Turbines In a large generator, a turbine provides the rotational mechanical energy for the generator. An electric utility power station will use a turbine, engine, or similar machine to drive an electric generator or another device that converts mechanical or chemical energy into electricity. Steam turbines, internal-combustion engines, gas combustion turbines, water turbines, and wind turbines are the most common methods to generate electricity.

The Transformer

Transformers allow electricity to be efficiently transported over long distances. Transformers are composed of two or more windings usually wrapped around a common core made iron. If the current flowing through the primary coil is fluctuating, then a current will be induced into the secondary winding. A steady (DC) current will not be transferred from one coil to the other. The coils are usually constructed so that they will have a small resistance. Copper coils are the most common type.