Chapter 15 QUIZ

D-C MOTORS

1. How does a d-c motor differ from a d-c generator in construction?

2. Motor action results from the reaction between two _____________.
3. What is motor action in a generator?
4. What is counter-EMF in a motor?
5. What effect does counter-EMF have on armature current?
6. What happens to the amount of counter-EMF if the motor is slowed down?

7. What effect does decreased counter-EMF have on the amount of current?

8. What is the principle function of a starter?
9. What are the two methods of reversing a motor?
10. What is standard Navy practice for reversing a motor?

Chapter 15 ANSWERS

D-C MOTORS

1. not at all. Essentially the two are alike in construction.

2. Magnetic fields.
3. The force set up by the two fields which tends to make the generator run as a motor.
    This is a Lenz's law illustration.

4. The induced voltage which opposes the applied voltage. Another Lenz's law illustration.
5. Counter-EMF controls the current by opposing the current's flow.
6. Counter-EMF decreases.
7. current will increase.
8. A starter decreases current to the armature by putting a resistance in the armature circuit.
9. Reverse leads to either the field or armature. not to both!
10. Reverse armature leads only.

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