PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 25)

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012-06247A Motor Accessory
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➂ Holding the armature in one hand, follow the wire from the slip ring to the left coil of the
armature and note the direction the wire is wound in the coil. Note where the wire enters
and exits the coil.
➃
Imagine that the AC current is in the positive half of the waveform. This means that
conventional current comes out of the terminal marked positive of the power supply and
enters the terminal marked negative. Use the right-hand rule to determine the direction the
magnetic field will flow at that instant: Grasp the coil with your fingers wrapped around
the coil in the direction of the current. (Current direction is described by convention as
being from the positive to the negative. Note that this is opposite of the direction of
electron movement.) Your thumb will point in the direction of the field (that is, toward the
north pole of the coil). Put a small piece of tape on the end of the coil that would be its
north pole at that instant.
➄
Follow the wire over to the right coil. Use the right hand rule to find the direction of the
north pole.
a) In this situation, is the direction of the north pole the same for the right and left coils?
b) In that case, can you say that, in this situation, the north pole of either the coils is in the
same direction as the north pole of the armature? Explain why.
c) True or False: In this AC motor, we can determine the direction of the magnetic field of
the armature at any instant by determining the direction of the north pole of either of the
two coils.
➅
Imagine that the AC current is in the negative half of the wave form. This means that
conventional current comes out of the terminal marked negative of the power supply and
enters the terminal marked positive. Repeat step 5 to determine which end of the armature
would be its north pole at that instant.
Is the north in this case on the same or opposite end of the armature as in step 5?
➆
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 the magnetic field would flow.
Is the north pole on the same arm of the armature as in step 5?
➇
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?
➈
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.