PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 23)

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012-06247A Motor Accessory
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EQUIPMENT NEEDED
•
Motor Accessory
•
multimeter
•
Variable Gap Magnet
•
patch cords
•
Digital Stroboscope or
•
power source that will deliver both
Digital Photogate Timer DC and AC current limited to 1.0 A
•
corrugated cardboard
Purpose
The purpose of this experiment is to demonstrate the operation of an AC synchronous motor in
terms of basic concepts of electromagnetism.
Theory
The Variable Gap Magnet (a permanent magnet) may be thought of as possessing a north pole
and a south pole that interact with the north and south poles of the armature (an electromagnet).
Like poles repel, while unlike poles attract. The armature rotates until its north pole is as close as
possible to the south pole of the permanent magnet (and also as far as possible from the north
pole). At that moment, the alternating current reverses its direction in the armature. The poles
likewise reverse, promoting another half-turn of the armature.
A better explanation involves an understanding of fields. The variable gap magnet produces a
magnetic field that passes through the gap between the pole pieces. When current passes through
the turns of the armature in the presence of the field, forces act to cause a torque that rotates the
armature. Inertia carries the armature past the position of no torque to the point where the torque
would force the armature back in the other direction. Instead, if the rotational speed of the
armature matches the frequency of the alternating current, the direction of current in the armature
will reverse at that instant, so that the torque continues to act in the original direction.
Setup
➀ Be sure you have the flat iron pole pieces placed on the two neodymium magnets of the Variable
Gap Magnet. (The iron pole pieces spread the magnetic field over a wider area.) Screw the larger
threaded portion of the shaft into the threaded hole in the magnet base. Insert the threaded end of
the shaft from above, screwing it in until 1 mm, or slightly less, of the threaded portion remains
above the upper surface of the base.
➁
Turn the magnet over and screw the retaining nut onto the smaller diameter threaded portion of
the shaft that protrudes through the bottom of the magnet base. Use firm finger pressure. Do not
over tighten.
Experiment 3: Operation of an AC Synchronous Motor