1. Electrical principles and technologies
Topic 6: Generators and Motors

2. Most of our electricity comes from the conversion of mechanical energy.
Mechanical energy is associated with any system with moving parts – for example, a rotating windmill, spinning turbines, or the moving water of rivers or tides.
A device that converts mechanical energy into electric energy is called an electric generator.

3. Electricity to Magnetism
The idea for the first electric generators dates back to a discovery by Hans Christian Oersted and André-Marie Ampère in 1820.
Describe the relationship the scientists observed between electricity and magnetism.
A compass needle turns when it is near a wire carrying electric current. Amount of deflection depends on amount of current. Reversal of current causes needle to deflect in other direction.

4. Electromagnets
An electromagnet is a strong temporary magnet, created by inserting a soft iron core into a coil of wire and then passing a current through the wire.
Michael Faraday is credited with discovering the basic principles of electromagnetism.
Each atom has a north and south pole.
In some materials such as iron, atoms group together into magnetic domains, in which all the north poles face the same way.
Unmagnetized objects have domains that are randomly arranged and so their magnetic effects cancel out.

5. Magnetism to Electricity
Electrical effects can be produced using a magnet.
A potential difference (_________) is “induced” in a wire when there is relative motion between the wire and a nearby magnet.
Maglev trains use repulsion between electromagnets on the train and electromagnets mounted between the tracks to suspend the entire train above the track, reducing friction and increasing efficiency.
MRI (magnetic resonance imaging) equipment is used to produce images of soft body tissues that cannot be examined using x-rays.

6. What’s in a Generator?
An AC generator, the most common form, has a coil of wire that rotates inside a stationary field magnet.
The coil is rotated by an external force, which is usually supplied by steam, falling water or wind.
Draw and describe how an AC generator works. (page 313)
As a coil of wire is rotated inside a magnet, electrons move along the wire in one direction. After ½ revolution of the wire loop, each side of the coil passes near the opposite pole of the magnet and the direction of current changes.

7. Electricity produced by an AC generator is called alternating current (AC) because it changes direction or “alternates”.
It is relatively easy to increase or decrease the voltage of alternating current.
In order to travel long distances through transmission lines, the voltage is increased.
For consumer use, the voltage must then be decreased by using transformers.
An electric transformer is used…
Not this type of transformer…

8. DC Generators
Generators can also produce DC (direct current), or current in only one direction.
A DC generator is often called a dynamo.
In a dynamo, the armature is connected to the outside circuit by a split-ring commutator.

9. AC vs. DC
AC-DC demo

10. Electric Motors: Electric to Mechanical Energy
An electric motor can be constructed in exactly the same way as a generator.
Instead of producing electricity, a motor uses electric energy to make a coil of wire spin between poles of a magnet.
The coil is connected to a source of electric energy.

11. DC Motors
A DC motor is rotated by magnetic forces between the field magnets and the armature, which acts as an electromagnet.

12. AC Motors AC motors are found in larger appliances.
List 4 appliances that operate using alternating current.
Dishwashers
Washing machines
Garage door openers
Furnaces

13. AC motors have a rotor made up of a ring of non-magnetic conducting wires connected at the ends and held in a laminated steel cylinder.
Surrounding the rotor is a stationary component called a stator.
The simplest form of stator is a two-pole electromagnet.

14. Internet Connect
The St. Louis motor was designed to teach how a DC motor works. Draw and label the St. Louis motor below.
St. Louis motor