PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 15)

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012-06247A Motor Accessory
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b) Both coils surround a single iron core on the armature, and each coil is capable of
temporarily magnetizing the core when electric current is running through it. Do the
actions of the two coils add to create a greater effect or cancel to create a reduced
effect? (Consider your answer to 6a above.)
➆
Turn the armature over 180° and imagine that the brush attached to the + lead is contacting
the other split ring of the commutator. Note the path of the wire from where it is attached
to the split ring to where it enters and exits from the coil on the right side of the armature.
Imagine a current running through the wire and use the right-hand rule to determine the
direction the magnetic field would flow. Is the north pole on the same end of the coil as it
was in step 5?
➇ Follow the wire over to the left 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) True or False? When the electric current is on, the two coils become electromagnets
with magnetic fields oriented in the same direction, which turns the armature into a single
electromagnet with its force oriented towards that same direction.
c) True or False: In the DC motor, you cannot determine the direction of the magnetic
field of the armature by determining the direction of the north pole of either of the two
coils.
d) What happens to the location of the armature’s north pole as the brush attached to the
+ lead touches the different sides of the split ring commutator?
e) Can you explain why the current in the armature is alternating, despite the fact that the
motor is supplied with direct current. (Hint: think about your answer to 8d.)
➈ Gently replace the armature onto the shaft with the split ring commutator down. Carefully
rotate the armature back and forth to separate the brushes and allow the commutator to
slip down between them. If necessary, insert a pencil or similar object between the brushes
to separate them. Use only the most delicate force to avoid bending the brushes and
necessitating adjustment or repairs.
Procedure—Part B
➀ Turn on the power. Adjust the output voltage to 6 volts.
➁
Use the small cylindrical ceramic magnet to check your predictions from steps 5 and 6