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


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