User's Manual

21
012-07210A Permanent Magnet Motor
7. Turn the armature over 180° and imagine that the AC current is in the positive half of the
waveform. Note the path of the wire from where it is attached to the slip ring to where it enters
and exits from the coil on the left side of the armature.
Use the right-hand rule to determine the direction that the magnetic field would flow.
Is the north pole on the same arm of the armature as in step 5?
8. Imagine that the AC current is in the negative half of the waveform. Use the right-hand rule to
find the armature’s north pole.
a) What can you say about the location of the armature’s north pole as the AC waveform
alternates from positive to negative?
b) What is the function of the slip-ring commutator?
9. Gently replace the armature onto the shaft. The dual slip-ring commutator should be down.
Carefully rotate the armature back and forth to separate the brushes and allow the commutator to
slip down between the brushes.
Procedure—Part B
1. Connect the motor to the power
source by one of these methods
(Figure 3.3):
• Insert banana plugs into the
openings in the ends of the
plastic brush holder;
• Grip the brass posts of the
brush holder with large
alligator clips; or
• Attach small alligator clips to
the ends of the brass strips that
serve as brushes.
Adjust the power source to
deliver 6 volts of DC current
limited to 1.0 amp. (Have your
teacher show you how if you
don’t know.)
2. Hold the armature in a position
like that shown in Figure 3.3.
Hold the ceramic magnet near the ends of the armature in order to establish which end is a north
pole and which is a south pole. The painted face of the magnet is its North Pole (north-seeking
pole). [You can verify this by hanging the magnet from a thread and observing that the painted
face points toward the North (toward the Earth’s north magnetic pole, located in northern
Canada).] If both poles of the ceramic magnet attract the armature, the pole with the stronger
attraction will be the opposite pole. Verify that the result of the tests agree with your results
from Step 3. Determine the polarity of the field magnets in the same way.
6 AMP MAX
RESET
ON
OFF
PASCO scientific
METER
PUSH FOR
CURRENT
DC CURENT
ADJUST
DC VOLTAGE
ADJUST
2
4
6
8
12
14
16
18
20
22
24
10
AC VOLTAGE ADJUST
2 - 24 VOLTS AC OUTPUT
0 - 24 VOLTS DC OUTPUT
8 AMP MAX
MODEL SF-9584 LOW VOLTAGE AC/DC POWER SUPPLY
Figure 3.3
Experimental Setup