Download AC DC •Motors •Generators - Northside College Prep High School

12/7/2012
DIRECT CURRENT - DC
•AC DC
•Motors
•Generators
http://www.ndted.org/EducationResources/HighSchool/Electricity/directcurrent
.htm
• Current flowing in one direction; as in the
batteries. Fuel cells and solar cells also supply DC.
• There is a supply of electrons that travel
through the component and wires.
ALTERNATING CURRENT - AC
• The electrons don’t flow through the circuit.
• Electrons vibrate in response to the electric field
provided by the outlet.
• In the USA, the direction of current is switching
back and forth 60 times each second or 60 Hertz.
• AC is produced by generators in power plants.
http://www.ndted.org/EducationResources/HighSchool/Electricity/alternatingcurren
t.htm
Did you understand?
• What does DC stand for; what does it mean?
• What does AC stand for; what does it mean?
• How is AC produced in the USA and how is it
delivered to your home?
• What is a common source of DC?
• What happens to the Voltage in AC and how
frequent does it change polarity?
• Does the electric company cell electrons, energy
or current?
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Electromagnetic forces and Motors
Did you understand?
• Use your hand and try to answer the following
problems.
Type of answers:
• west (left) or north(up)
• into page, no force, south(down)
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Torque on a current-carrying loop of wire. The
shaft feels magnetic forces that produce a
clockwise torque and it spins.
MOTOR: based on Torque on a looped wire
Motors are the most common application of
magnetic force on current-carrying wires.
Motors have loops of wire in a magnetic field.
When current is passed through the loops, the
magnetic field exerts torque on the loops, which
rotates a shaft.
Electrical energy is converted to mechanical work
in the process.
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Did you understand?
• From what you have observed in this
experiment here, can you explain how an
electric motor works?
• Why is important that alternating current is
supplied to our houses
• Which appliances use motors with high speed
at home?
Electric Motor vs Electric Generator:
http://www.youtube.com/watch?v=d_aTC0iKO68
Electric Motor
• Electricity-Voltage  Movement
Electric generator
• Movement  Voltage-Electricity
GENERATOR: based on faraday’s Law
Faraday’s Law (change in B can cause a I):
http://phet.colorado.edu/en/simulation/faradays-law
• LAB Faraday’s:
http://phet.colorado.edu/en/simulation/faraday
Also select the generator tab
Did you understand?
• Explain how current can be produced ina conducting
wire without contact.
• Explain an electric potential difference can be produced
by a varying magnetic field.
• So, the relative movement of a wire to a magnetic field
can generate movement of charges or electric potential
(field).
• Therefore, movement can be used to generate electric
voltages and fields. This is the role of power plants.
Answer the following slides.
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What would you expect the light to do if
you change the coils from 2 to 3 and you
move the magnet the same speed?
A. Show the same
brightness
B. Show less
brightness
C. Show more
brightness
What will happen if you
switch the battery so
that the positive end is
on the right?
A. The electrons will go faster
B.The electrons will go the slower
C.The compass will switch
directions
D.The electrons will go the other
direction
E.Two of the above.
DIRECT CURRENT
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ALTERNATING CURRENT - AC
DIRECT CURRENT
After reading this section you will be able to do the following:
Explain what DC stands for and what it means.
Define what a good source of DC would be.
Now that we have a fairly good understanding of basic electricity terms and concepts, let's take a
closer look at some more details of the electrical current itself.
The battery we have been using for a current/voltage source generates direct current, which simply
means the current flows in only one direction.
As long as electrons are flowing through the atoms of the circuit, work is being done. We can see
that work is being done in this circuit because it lights the light bulb. The actual amount of
electrons that are flowing is determined by the type and size of the battery as well as by the size
and type of the light bulb. We could reverse the polarity of the battery by switching the contacts
(wires), and the current would flow in the opposite direction and the bulb would still light.
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Either way the battery is connected to the circuit, current can only flow in one direction. Direct
current (DC) can also be generated by means other than batteries. Solar cells, fuel cells, and even
some types of generators can provide DC current.
Review
DC, or direct current means the electrical current is flowing in only one direction in a circuit.
Batteries are a good source of direct current (DC).
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ALTERNATING CURRENT
After reading this section you will be able to do the following:
Define what AC stands for and what it means.
Explain how AC is created and delivered to different places.
Discuss the differences between AC and DC.
AC is short for alternating current. This means that the direction of current flowing in a circuit is constantly being
reversed back and forth. This is done with any type of AC current/voltage source.
The electrical current in your house is alternating current. This comes from power plants that are operated by the
electric company. Those big wires you see stretching across the countryside are carrying AC current from the
power plants to the loads, which are in our homes and businesses. The direction of current is switching back and
forth 60 times each second.
This is a series circuit using an AC source of electricity. Notice that the light bulb still lights but the electron current
is constantly reversing directions. The change in direction of the current flow happens so fast that the light bulb
does not have a chance to stop glowing. The light bulb does not care if it is using DC or AC current. The circuit is
delivering energy to the light bulb from the source, which, in this case, is a power plant.
Review
AC, or alternating current means the electrical current is alternating directions in a repetitive pattern.
AC is created by generators in power plants, and other sources. This AC current is delivered to our homes and
businesses by the power lines we see everywhere.
The frequency of repetition of this current is 60 Hertz. This means the direction of the current changes sixty times
every second.
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ELECTROMAGNETIC INDUCTION
• After reading this section you will be able to do
the following:
• Explain how current can be induced in a
conductor without making contact.
• Describe the process of induction.
• We have now seen that if electrical current is
flowing in a conductor, there is an associated
magnetic field created around the wire. In a
similar manner, if we move a wire inside a
magnetic field there will be an electrical current
that will be generated in the wire.
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