Transcript U3e L16 4-9 Electricity and Magnetism 9

April 9, 2008
DRILL
1. Have out your electric motor project.
2. Who was the first person to successfully create an
electric motor? Michael Faraday
3. What was this man’s profession? Physicist and
Chemist
4. What did he discover?
Electric currents create a magnetic field and
magnetic fields induce electric currents.
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ELECTRIC MOTORS
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Electric motors are used everyday in many ways.
A motor’s purpose is to turn electrical energy into
mechanical energy.
Motors work on simple principles of magnetism:
• Opposite poles _____________
ATTRACT
• Like poles _____________
REPEL
N
S
S
S
N
N
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ELECTRIC MOTORS
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An electric current produces a magnetic field.
Electric current through a coil of wire creates an
electromagnet.
• What is the benefit of creating a magnet with
electricity?
– It can be turned on and off.
– The strength and direction of the magnetic
poles can be controlled by altering the strength
and direction of the electric current.
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ELECTRIC MOTORS
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What will happen now?
–
The electromagnet and the permanent magnet will
ATTRACT each other.
N
S
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The electromagnet and the permanent magnet will
REPEL each other.
S
N
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Back to our magnet:
Suppose we create an electromagnet like below.
What will happen?
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ELECTRIC MOTORS
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What would happen if we put an axle through the
middle of the permanent magnet, then turned on
the electromagnet?
This is how a motor rotates.
The electromagnet is turned on and off so that the
permanent magnet is attracted, then repelled,
then attracted, then repelled….and so on.
N
S
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ELECTRIC MOTORS
Let’s look at your electric motor project
• Identify the following:
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Permanent Magnets
Electromagnet
How is the electromagnet powered?
What is the circuit that the current must follow?
If your motor were working ideally, how is the
electromagnet turned on and off to cause
CONSTANT rotation?
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The commutator turns the electromagnet on and off
at particular times.
When does it turn the magnet on?
When does it turn the magnet off?
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ELECTRIC MOTORS
What is a schematic?
A schematic is a diagram that represents the
elements of a system without using realistic pictures.
How would a schematic of your electric motor look?
Switch = Commutator
Load
V = 9V
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ELECTRIC MOTORS
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Now that you know what switches look like in
electrical schematics, draw an electrical schematic
for a lamp plugged into a wall outlet.
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Remember that AC power supplies look like
in electrical schematics.
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ELECTRIC MOTORS
Lamp
120 V
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HOMEWORK
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Tomorrow is a review for Monday’s test on
Electrical Technology.
Begin studying tonight!
Any problem/question that you’ve seen in class
is a candidate for the test.
Come to class with any questions you may have.
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