DC MOTORS

Question 1

1. Which of the following statements is false for a series wound DC motor?
   A. The speed decrease with increase of resistance in the armature circuit
   B. The speed increases as the flux decreases
   C. The speed can ve controlled by a diverter
   D. The speed can be controlled by a shunt field regular

Answer 1

D. The speed can be controlled by a shunt field regular

Question 2

2. Which of the following statements is false?
   A. A series wound motor has a large starting torque
   B. A shunt wound motor must be permanently connected to its load.
   C. The speed of series wound motor drops considerably when load is applied
   D. A shunt wound motor is essentially a constant speed machine

Answer 2

B. A shunt wound motor must be permanently connected to its load.

Question 3

3. The speed of a DC motor may be increased by
   A. Increasing the armature current
   B. Decreasing the field current
   C. Decreasing the applied voltage
   D Increasing the field current

Answer 3

B. Decreasing the field current

Question 4

4. The effect of inserting a resistance in series with field winding of a shunt motor is to.
   A. Increase the magnetic field
   B. Increase the speed of the motor
   C. Decrease the armature current
   D. Reduce the speed of the motor

Answer 4

B. Increase the speed of the motor

Question 5

5. With a DC motor, rhe starter resistor
   A. Limits the armature current to a safe starting value
   B. Controls the speed of the machine
   C. Prevents the field current flowing through and damaging the armature
   D. Limits the field current to a safe starting value

Answer 5

A. Limits thr armature current to a safe starting value

Question 6

6. If the two leads of a DC series motor are reversed, which of the following events will happen?
   A. It becomes a generator
   B. It runs in the same direction
   C. It will not run
   D. It will run in the reverse direction

Answer 6

B. It runs in the same as direction as before

Question 7

7. The rotating part of a DC motor is known as
   A. Pole
   B. stator
   C. Carbon brush
   D. Armature

Answer 7

D. Armature

Question 8

8. The counter emf of a DC motor is zero when the
   A. Armature is not turning
   B. Armature just begins to turn
   C. Motor is at rated speed
   D. Motor is almost up to rated speed

Answer 8

A. Armature is not turning

Question 9

9. The speed of the DC motor is directly proportional to its
   A. Armature current
   B. Flux per pole
   C. Back emf
   D. Torque

Answer 9

C. Back emf

Question 10

10. Which of the following statements is false?
    A. A DC motor converts electrical energy to mechanical energy
    B. The efficiency of the DC motor is the ratio input power to output power
    C. a DC generator converts mechanical power to electrical power
    D. The efficiency of the DC generator is the ratio output power to input power

Answer 10

B. The efficiency of the DC motor is the ratio input power to output power

Question 11

11. Which of the following is false?
    A. A commutator is necessary as part of DC motor to keep the armature rotating in the same direction
    B. A commutator is necessary as part of a DC generator to produce unidirectional voltage at the terminald of the generator
    C. The field winding of a DC machine is housed in slots on the armature
    D. The brushes of DC machine are usually made of carbon and do now rotate with the armature

Answer 11

C. The field winding of a DC machine is housed in slots on the armature