PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 36)

Motor Accessory 012-06247 A
32 ¨
T T
H I
ý
G N
L O
M I
R A N
A D J U
M A
O U
T P
A M
P L
I T
P I
- 9
5 8
7 C
D I
G I
TA
L
F U
N C
T I
O N
WA
V E
F
I N P
G N
E X T E R
F R
E Q
U E
N C
Y
-
HE
RT
Z
= D C
400
400
b) The slip-ring commutator connects the armature to the power source by way of the brushes
and enables the current to travel in an unbroken stream from the positive to the negative termi-
nals of the power supply.
Part B
➂ a) The armature vibrates or pulses.
b) This happens because the alternating current causes the polarity of the armature to reverse
with each AC cycle.
➃ a) It vibrates or pulses at the same frequency, but with less force.
b) This happens because the rate at which the polarity reverses is the same, but the force of the
induced magnetic flux of the armature decreases with the decreased voltage.
➄
a) The rate of vibration is lessened, and the strength of the pulsation is increased.
b) The halving of the cycle rate of the AC results in halving the rate of reversal of polarity in
the armature, while the increase in voltage results in the increase in strength of the pulsations.
➈ The rotational speed of the armature does not change when you change the voltage.
➉
The speed varies directly with the AC frequency.
Experiment 4
•
Remind students not to prolong situations when the armature is not spinning and the power is
connected—the coils will overheat.
•
If the power source does not limit the current to 1 ampere, use an appropriate resistor (e.g.
0.51 ohm, 1 watt) in series to limit the current.
Questions
4, 7, and 9 (see diagram below)
i i
= current
N
S
N
S
i
i
i
i
i
i