PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 32)

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Motor Accessory 012-06247A
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Turn on the power supply (10 volts DC) for the next step.
➤ Do not leave the power connected to the motor for extended periods, particularly
with the armature not rotating, because the windings may overheat.
➈ Use the small cylindrical ceramic magnet to check your predictions from steps 5 and 7 above. 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).] With the
armature and power supply leads oriented as in Figure 2, hold the ceramic magnet near the
ends of the armature. 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 labeling of the figure. Determine the polarity of the U-shaped core in the same way.
Label its poles N and S in Figure 2.
➉ Predict the direction the armature will rotate when you release it from the position shown in Figure
2. If the motor does not start up immediately, try turning it by hand in the opposite direction.
Turn off the power and reverse the leads to the brushes. Before turning the power on,
predict the direction of rotation. Turn the power back on and immediately try spinning the
motor to start it. If it doesn’t start, try spinning it in the other direction.
Predict the effect on the motor’s speed of decreasing the voltage to 8 volts.
Predict the effect of replacing the direct current with alternating current of 10 volts at 12 Hz.
Also predict the effect of then reducing the voltage to 8 volts. Test these predictions.
Predict the effect of raising the frequency to higher values such as 15, 20, 25, and 30 Hz.
Test this prediction. Try to explain the result. (The explanation involves the concept of
inductive reactance.)
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