PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 21)

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012-06247A Motor Accessory
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(b) Must conventional current enter the coil, or leave the coil, from the upper brush, in order
to make the armature act as you described in 9 (b) above?
Use a sensitive galvanometer or a digital multimeter set on a DC millivolt range to test your
predictions. When conventional current enters the positive terminal of a meter, the needle
of a traditional meter will move to the right, and the number displayed by a digital meter
will be positive (or no sign will be displayed). If conventional current enters the negative
terminal, the needle will swing left (unless prevented by a peg in the meter) and, in a digital
meter a negative result will be displayed.
a) Test your predictions to 10 (a) and (b) above: After connecting the meter to the brushes,
repeat the two 90-degree rotations, taking about one-half second for each. Comment
on your findings.
Using the same reasoning as before, predict the direction(s) of the current during the next
180-degree rotation following the one you just made.
(b) Test your predictions with the meter and comment.
(c) What is different if the armature is rotated in the opposite direction?
As the armature rotated, the current changed both in magnitude and direction. This is
called alternating current. If this generator were rotated at 3600 revolutions per minute,
what would the frequency of the alternating current be?
Part B: DC Generator
➀
Review steps 1 and 5. Then remove the armature and install it with the split ring commuta-
tor down between the brushes.
➁ Connect the meter and rotate the armature slowly, at a rate of about one complete revolu-
tion in two seconds.
(a) How does the meter respond?
(b) How does the meter respond when the armature is rotated in the opposite direction?
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