Chapter 23-- AC Current

Section 20.2: Motors, Generators, and Transformers

Section 20.3: Electromagnetic Induction

Faraday

Michael Faraday was an English chemist and physicist. He is credited with discovering that a changing magnetic field produces an electric current.

His experiment used two loops of wire– when power flowed through the first, it produced a magnetic field. Whenever the power was turned on or off in this coil, a spike of current was detected in the second coil.

Go Watch This Video!

Electromagnetic Induction

​Electromagnetic Induction: inducing an electric current in a circuit by using a changing magnetic field.

The greater the rate of change of the magnetic field (the faster it grew or got smaller) the greater the induced current

Magnetic Flux

• Magnetic Flux is just how many magnetic field lines pass through a certain area. If something is parallel to the field lines, there is zero flux. Perpendicular objects have high flux.

• Changing flux causes electromagnetic induction. Changing the orientation of a wire loop in a constant magnetic field will produce a current. This is the basis of electric generators.

Electric Generators

Test Prep Question: What is an Electric Generator? How does it work?

How do they work?

The wire rotates in between the magnets. This rotation causes flux in the system. Because the wire is constantly spinning, there is constant flux. This causes induction and produces electricity.

Electric Motors

Test Prep Question: How are Electric Generators and Electric Motors the same, and how are they different?

Electric Motors

In an electric motor, electricity is applied to the system. The electricity induces flux in the system. This causes the wire to begin to spin.

Multiple Select

How are Generators Like Motors?

• They both use magnets

• They both involve motion

• They both use induction

• They both need flux to work

Multiple Select

Which of the following statements are true?

• Motors use electricity to make motion

• Motors use motion to make electricity

• Generators use electricity to make motion

• Generators use motion to make electricity

Electrical Safety Devices

• Fuses and Circuit Breakers

• GFCI Outlets

• Grounded and Polarized Plugs

Circuit Breakers and Fuses

• Both turn off the electricity when they detect too much current flowing

• Fuses use a strip of wire that melts and breaks-- can only be used once

• Circuit breakers use complex coiled wires and bimetallic strips-- can be 'reset' like a light switch and used again and again

GFCI Outlet

Ground Fault Circuit Interrupters look for changes in current and shut off the power when they are detected. These should be used anywhere where electricity and water could mix

Multiple Choice

Which of these is a GFCI most closely related to?

• Fuse

• Circuit Breaker

Grounded and Polarized Plugs

Outlets must have two holes in order to work. Grounded plugs add a third "ground" hole that carries away extra electricity in case of a short. Polarized plugs have the two holes be different sizes so devices cannot be plugged in upside down.

Multiple Select

Which of these are polarized plugs?

Multiple Select

Which of these is are grounded plugs?

Multiple Choice

Which of these is a GFCI??

Transformers

• Transformers are used to change the current and voltage in a system

• I and V are inverse-- as current goes up, voltage must go down

Transformers

Transformers use coils around an iron core. The coils induce current. The more coils are in the wire, the higher the voltage.

Multiple Choice

Which side of this transformer has higher current?

• The Side with more Coils

• The Side with fewer Coils

Induction Motors

• Induction motors work very similarly to regular electric motors, except all of the components are contained inside instead of having exposed slip rings and brushes.

• By having no exposed parts, they can't produce sparks that could trigger an explosion