PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 34)

Motor Accessory 012-06247 A
30 ¨
Part B
➂
Results of the test should agree with predictions.
➃
Clockwise, if the leads are connected exactly as shown in Figure 2 and the north pole of the
Variable Gap Magnet is on the left.
➄ a) It should rotate in the counter-clockwise direction.
b) Answers will vary. If students explain using the concept of “opposite magnetic poles at-
tract and same poles repel,” they will say something like, “As the opposite sides of the split-
ring commutator come in contact with the + lead of the DC power supply, the location of the
north pole of the electromagnet alternates, causing it to seek alternating poles on the perma-
nent magnet.”
If student responds using the concept of torque they might say, “The flux lines of the perma-
nent magnet extend from its north to south pole and interact with the flux lines of the electro-
magnet, producing a torque that spins the armature. Inertia carries the armature past the posi-
tion of no torque to the point where the torque would force the armature back in the other di-
rection. However, at that point the commutator reverses the direction of current in the arma-
ture so the torque continues to act in the original direction.”
➅
a) The motor speeds up.
b) The motor’s speed is directly dependent on the voltage of the DC current.
Experiment 2
Questions:
Part A: AC Generator
➆
(a) It increased.
(b) An emf (electromotive force or voltage) will be induced in the coil.
➇ (a) It decreased.
(b) An emf will be induced.
(c) The emf will be opposite in sign (or direction) in the two steps because the change in flux
within the turns is opposite in the two cases. (In one case it is increasing, in the other case,
decreasing.)
➈ (a) It should be a north pole, to repel the N pole of the Variable Gap Magnet and thus to op-
pose the motion.
(b) a south pole
➉
(a) It must enter the coil from the upper brush.
(b) It must leave the coil and pass into the upper brush.
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If the negative lead of the meter is connected to the upper brush and the positive lead is con-
nected to the lower brush, then the meter will show positive (or move right) curing the first
quarter turn, and negative (needle will move left) during the second quarter turn.
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(a) During the 3rd quarter turn, the current will leave the coil and pass into the upper brush;
during the 4th quarter turn, the current will enter the coil from the upper brush.
(b) Assuming as before that the negative lead of the meter is connected to the upper brush
and the positive lead is connected to the lower brush, during the 3rd quarter turn, the meter
will show negative (or move left); during the 4th quarter turn, the meter will show positive
(or move right).
(c) Every result will be reversed.
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3600 cycles per minute, or 60 cycles per second, more properly termed 60 Hertz, or 60 Hz