DC motor mcq questions answers part2

Q1. What will happen if the back EMF of a D.C. motor vanishes suddenly?
(A) The motor will stop
(B) The motor will continue to run
(C) The armature may burn
(D) The motor will run noisy

Q2. For which types of D.C. motor, dynamic braking is generally used ?
(A) Shunt motors
(B) Series motors
(C) Compound motors
(D) All of these

Q3. The speed of a D.C. shunt motor can be increased by
(A) increasing the resistance in armature circuit
(B) increasing the resistance in field circuit
(C) reducing the resistance in the field circuit
(D) reducing the resistance in the armature circuit

Q4. Which one of the following is not necessarily the advantage of DC motors over AC motors?
(A) Low cost
(B) Wide speed range
(C) Stability
(D) High starting torque.

Q5. The plugging gives the
(A) zero torque braking
(B) smallest torque braking
(C) highest torque braking
(D) none of the above

Q6. Which of the following motors has the poorest speed control?
(A) Differentially compounded motor
(B) Cumulatively compounded motor
(C) Shunt motor
(D) Series motor

Q7. The armature voltage control of D.C. motor provides
(A) constant voltage drive
(B) constant current drive
(C) constant torque drive
(D) none of the above

Q8. The type of braking by interchaning the terminals of armature of D.C. motor
(A) regenerative
(B) plugging
(C) dynamic braking
(D) none of the above

Q9. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
(A) increases
(B) decreases
(C) remains same
(D) become zero

Q10. Ward-Leonard control is basically a
(A) voltage control method
(B) field diverter method
(C) field control method
(D) armature resistance control method

Q11. Which of the following is the main disadvantage of the Ward-Leonard control method?
(A) high initial cost
(B) high maintenance cost
(C) low efficiency at Hght loads
(D) all of these

Q12. In Ward-Leonard control the lower limit of speed is imposed by
(A) residual magnetism of the generator
(B) core losses of motor
(C) mechanical losses of motor and generator together
(D) None of these

Q13. The hysteresis loss in a D.C. machine least depends on
(A) Frequency of magnetic reversals
(B) Maximum value of flux density
(C) Volume and grade of iron
(D) Rate of flow of ventilating air

Q14. Which of the following loss in a D.C. generator varies significantly with the load current?
(A) Field copper loss
(B) Winding loss
(C) Armature copper loss
(D) None of the above

Q15. D.C. shunt motors are used for driving
(A) trains
(B) cranes
(C) hoists
(D) machine tools

Q16. Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?
(A) Hysteresis losses
(B) Eddy current losses
(C) Copper losses
(D) Winding losses

Q17. D.C. generators normally has maximum efficiency around
(A) full-load
(B) rated r.p.m.
(C) rated voltage
(D) all of the above

Q18. D.C. generators are installed near the load centres to reduce
(A) iron losses
(B) line losses
(C) sparking
(D) corona losses

Q19. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity?
(A) Swinburnes test
(B) Winding test
(C) Field test
(D) Brake test

Q20. Which method of braking is generally used in elevators?
(A) Plugging
(B) Regenerative braking
(C) Rheostatic braking
(D) None of the above