Generators and motors  (Page 2/3)

In an AC generator the two ends of the coil are each attached to a slip ring that makes contact with brushes as the coil turns. The direction of the current changes with every half turn of the coil. As one side of the loop moves to the other pole of the magnetic field, the current in the loop changes direction. The two slip rings of the AC generator allow the coil to turn without breaking the connections to the load circuit. This type of current which changes direction is known as alternating current.

Dc generator

A simple DC generator is constructed the same way as an AC generator except that there is one slip ring which is split into two pieces, called a commutator, so the current in the external circuit does not change direction. The layout of a DC generator is shown in [link] . The split-ring commutator accommodates for the change in direction of the current in the loop, thus creating direct current (DC) current going through the brushes and out to the circuit.

The shape of the emf from a DC generator is shown in [link] . The emf is not steady but is the absolute value of a sine/cosine wave.

Ac versus dc generators

The problems involved with making and breaking electrical contact with a moving coil are sparking and heat, especially if the generator is turning at high speed. If the atmosphere surrounding the machine contains flammable or explosive vapors, the practical problems of spark-producing brush contacts are even greater.

If the magnetic field, rather than the coil/conductor is rotated, then brushes are not needed in an AC generator (alternator), so an alternator will not have the same problems as DC generators. The same benefits of AC over DC for generator design also apply to electric motors.While DC motors need brushes to make electrical contact with moving coils of wire, AC motors do not. In fact, AC and DC motor designs are very similar to their generator counterparts. The AC motor is depends on the reversing magnetic field produced by alternating current through its stationary coils of wire to make the magnet rotate. The DC motor depends on the brush contacts making and breakingconnections to reverse current through the rotating coil every 1/2 rotation (180 degrees).

Electric motors

The basic principles of operation for a motor are the same as that of a generator, except that a motor converts electrical energy into mechanical energy (motion).

Motor

An electric motor converts electrical energy into mechanical energy.

If one were to place a moving charged particle in a magnetic field, it would feel a force called the Lorentz force .

The Lorentz Force

The Lorentz force is the force experienced by a moving charged particle in a magnetic field and can be described by:

$$F=q\times v\times B$$

where

$F$ is the force (in newtons, N)

$q$ is the electric charge (in coulombs, C)

$v$ is the velocity of the charged particle (in $\mathrm{m}.{\mathrm{s}}^{-1}$ ) and

$B$ is the magnetic field strength (in teslas, T).