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Name _________________________ Section ___________________
1103 Period 23: Alternating Current Motors
Activity 23.1 Is Induced Current Alternating or Direct Current?
1) Generating AC and DC current
a) Move a magnet into and out of the small coil of wire with red and green bulbs
attached. How must you move the magnet so that the red bulbs light and then the
green bulbs light?
b)
Is the current that you induce as you move the magnet in and out of the coil
direct current (DC) or alternating current (AC)? _________
How do you know?
c)
Connect the hand-cranked generator to the coil with red and green bulbs and
turn the crank. Are you generating AC or DC current?
Activity 23.2 Do Alternating Current Motors Need Commutators?
2) Synchronous motor: Connect a solenoid to the screws on the base of a step-down
transformer. Plug the transformer in the power strip.
a)
Hold a magnaprobe (a permanent magnet that spins and is attached to a handle)
vertically at one end of the solenoid’s metal core. Use your finger to start the
mangnaprobe spinning. Explain why the magnaprobe continues to spin.
3) Universal motor are AC motors with commutators: Your instructor will demonstrate
a motor that operates on alternating current, but uses a commutator.
a) Explain how the rotation of this motor differs from a DC motor, such as the St. Louis
motor, and from a synchronous AC motor.
Activity 23.3: What Is an Induction Motor?
4) Induction motors: Your instructor will demonstrate several induction motors.
a)
What happens when your instructor holds a disc and a shield near the large solenoid?
b)
A watt hour meter is an example of an induction motor. How is the watt hour
meter similar to the spinning disc your instructor held near the large solenoid?
c)
Explain what causes the rotor in an induction motor to turn.
d)
Examine the small black induction motor on your table. Why doesn’t this motor
need a permanent magnet?
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Activity 23.4: Building a Buzzer
5) Directions for Building the Buzzer: Step 1
a) Cut off approximately 3 meters of coated
copper wire from the wire spool.
b) Wrap the wire around the nail that is attached
to a small board. Wrap the wire leaving
about 10 cm of each end of the wire
free.
c) With a piece of sandpaper, remove the red insulating coating from 2 cm of both
ends of the wire. Be sure to remove all the insulation so that electrical contact can
be made.
d) Which component of your buzzer did you just make? _________________________
Step 2
e) Bend a large paper clip, which is made of steel and is magnetic, as shown below.
f) Position the paper clip on the board so that the long, horizontal part of the paper clip
is about one millimeter above the top of the nail and the large loop of the clip is
centered over the nail.
g) Staple the small loop of the paper clip firmly to the board using at least two staples
so that the paper clip does not wiggle.
h) Bend the large loop of a second large paper clip as shown in the diagram. Place the
second clip so that this straight section lies just over the end of the first paper clip as
shown below.
i)
Firmly staple the small loop of the second paper clip to the board.
The large loop is bent
and placed just above
the first paper clip.
The first paper clip lies just
above the nail head and just
under the second paper clip.
The small loop of the second paper
clip is stapled to the board.
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Step 3
j) Take one end of the copper wire wrapped around the nail and wrap it several times
around the base of the paper clip. Make sure the bare portion of the copper wire is
in contact with the paper clip.
k) Attach the other end of the copper wire to one clip lead from a 3-battery tray.
l)
Using another clip lead, attach the other end of the 3-battery tray to the small loop
of the second paper clip that is stapled to the board.
m) Important: Before connecting your buzzer to batteries, make sure the two paper
clips are making contact. When you push down on the first paper clip until it
touches the nail head, the two paper clips should no longer be in contact.
n) If adjusted properly, the buzzer should begin to buzz when the clip leads are
connected. (You may need to adjust the positions of the paper clips relative to the
nail head and to each other.)
The second paper clip
lies just above the
first paper clip.
6)
The first paper clip lies just
above the nail head.
Wire stripped of insulation and
wrapped around the paper clip.
How does the buzzer work?
a) Why is it necessary for the paper clip and the nonmagnetic wire to break
contact?
b) What causes a changing current in the buzzer?
c) What causes the paper clip to move up and down?
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d) On the diagram below, identify the components of the buzzer.
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Name _________________________ Section ___________________
Period 23 Exercises: Alternating Current Motors
Write answers to the questions below. This sheet with your answers should be turned in
at the beginning of Period 24.
1. Identifying types of motors:
We have studied four types of motors: the St. Louis motor, synchronous motor,
universal motor, and induction motor. Which type of motor fits each description
below? Write the type of motor on the blank line following each description.
a)
alternating current, electromagnets, and a commutator
____________
b)
alternating current, one electromagnet, and an induced current ______
c)
permanent magnet(s) and a commutator
d)
alternating current, single speed, no commutator ___________________
________________
2. Applying induced current and magnetism:
A watt hour meter is an example of an induction motor. The meter’s spinning
disc measures the electricity used by homes and businesses. Explain what
causes the disc to spin.
3. Explaining the buzzer:
a)
The buzzer you built in class has one magnetic field. What is the source
of this magnetic field?
b)
Would this buzzer work if two pieces of bare copper wire were used
instead of the two steel paperclips? Why or why not?
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