D.C. Machines & Batteries MCQs – DAE Electrical Engineering

1. The main function of a commutator in a DC machine is to:
(A) Convert AC to DC
(B) Reverse the direction of current in the armature winding
(C) Reduce losses in the machine
(D) Control speed of the machine

2. In a DC shunt motor, the field winding is:
(A) Connected in parallel with the armature
(B) Connected in series with the armature
(C) Always connected to a separate source
(D) Not connected at all

3. Which type of DC motor is generally used in cranes and hoists due to high starting torque?
(A) Shunt motor
(B) Series motor
(C) Compound motor
(D) Permanent magnet motor

4. A battery’s capacity is usually rated in:
(A) Volts
(B) Amperes
(C) Ampere-hours
(D) Watts

5. The back EMF in a DC motor:
(A) Opposes the applied voltage
(B) Aids the applied voltage
(C) Is zero at full load
(D) Is constant regardless of speed

6. The main loss in a DC machine due to magnetic hysteresis is called:
(A) Copper loss
(B) Iron loss
(C) Friction loss
(D) Mechanical loss

7. In a DC series motor, if the load is removed, the speed:
(A) Remains constant
(B) Decreases
(C) Increases drastically
(D) Increases slightly

8. Which of the following DC machines can operate as both motor and generator?
(A) Shunt
(B) Series
(C) Compound
(D) All of the above

9. The armature reaction in a DC machine causes:
(A) Flux weakening in the main poles
(B) Increase in field flux
(C) No effect on the machine
(D) Automatic speed control

10. Overcharging of a lead-acid battery may cause:
(A) Gassing and loss of water
(B) Increase in capacity
(C) Reduced voltage
(D) Self-discharge

11. In a battery, sulfation occurs when:
(A) Battery is overcharged
(B) Battery is deeply discharged and left unused
(C) Properly maintained
(D) Using AC current

12. The torque of a DC motor is proportional to:
(A) Armature current
(B) Back EMF
(C) Terminal voltage
(D) Load resistance

13. In a separately excited DC motor, the field is supplied from:
(A) The same supply as the armature
(B) A separate independent source
(C) No external supply
(D) Series winding

14. The series field winding in a compound DC motor:
(A) Provides constant excitation
(B) Provides additional torque at high load
(C) Reduces speed
(D) Reduces losses

15. Armature reaction is most pronounced in:
(A) Shunt motor
(B) Series motor
(C) High-load DC machine
(D) Low-power DC machine

16. Commutation in a DC motor refers to:
(A) Starting the motor
(B) Reversing current in each coil
(C) Changing voltage
(D) Speed control

17. The no-load speed of a DC shunt motor:
(A) Is equal to rated speed
(B) Increases with load
(C) Remains nearly constant
(D) Decreases sharply with load

18. The EMF equation of a DC generator is:
(A) E = V × I
(B) E = V/I
(C) E = IR
(D) E = P × Φ × N × Z / 60 × A

19. Which type of battery is widely used in UPS systems?
(A) Lead-acid
(B) Alkaline
(C) Nickel-cadmium
(D) Zinc-carbon

20. A DC shunt generator’s terminal voltage:
(A) Rises sharply with load
(B) Remains nearly constant
(C) Drops linearly with load
(D) Fluctuates randomly

21. The efficiency of a DC motor is maximum at:
(A) Full load
(B) Half load
(C) No load
(D) Quarter load

22. The main advantage of a DC shunt motor is:
(A) High starting torque
(B) Constant speed
(C) Simple design
(D) Low cost

23. In a lead-acid battery, during charging, the process that occurs at the positive plate is:
(A) Lead sulfate formation
(B) Conversion of lead dioxide to lead
(C) Electrolysis of water
(D) Oxidation of hydrogen

24. A DC compound motor is preferred when:
(A) Constant speed is required under varying load
(B) High starting torque is required
(C) Only low power is needed
(D) Small size is necessary

25. Which battery type has the highest energy density?
(A) Lead-acid
(B) Nickel-cadmium
(C) Lithium-ion
(D) Alkaline

26. DC series motors are unsuitable for:
(A) Traction
(B) Lifts
(C) Light-load constant-speed applications
(D) Cranes

27. Which type of DC motor has both series and shunt field windings?
(A) Shunt motor
(B) Series motor
(C) Compound motor
(D) Permanent magnet motor

28. The purpose of a starter in a DC motor is to:
(A) Reduce starting current
(B) Increase speed
(C) Reverse rotation
(D) Reduce voltage

29. The main disadvantage of a DC series motor is:
(A) Poor starting torque
(B) Speed varies greatly with load
(C) Requires complex control
(D) Low efficiency

30. Which of the following affects the EMF of a DC generator?
(A) Armature speed
(B) Field flux
(C) Both A and B
(D) Neither A nor B

31. In a battery, electrolyte functions as:
(A) Conductor of ions
(B) Mechanical support
(C) Voltage regulator
(D) Thermal insulator

32. A battery’s life can be extended by:
(A) Overcharging
(B) Regular maintenance and avoiding deep discharge
(C) Using AC supply
(D) Using improper electrolyte

33. The most common material for DC motor brushes is:
(A) Copper
(B) Graphite
(C) Aluminum
(D) Iron

34. Increasing the armature voltage of a DC motor:
(A) Increases speed
(B) Decreases speed
(C) Has no effect
(D) Reduces torque

35. Interpoles in a DC machine are used to:
(A) Increase speed
(B) Compensate for armature reaction
(C) Reduce losses
(D) Improve insulation

36. Compensating windings in a DC machine are used to:
(A) Improve power factor
(B) Reduce sparking at brushes
(C) Increase EMF
(D) Reduce copper losses

37. DC shunt motors are suitable for:
(A) Constant-speed applications
(B) Lifts
(C) High starting torque applications
(D) Cranes

38. The series field winding in a DC motor:
(A) Provides constant excitation
(B) Reduces losses
(C) Reduces speed
(D) Provides high torque at low speeds

39. Overheating of a DC motor may be caused by:
(A) Excessive load
(B) Low voltage
(C) Proper ventilation
(D) Correct wiring

40. Lead-acid batteries are:
(A) Non-rechargeable
(B) Zinc-carbon type
(C) Primary cells only
(D) Rechargeable

41. The starting torque of a DC series motor is:
(A) Low
(B) High
(C) Zero
(D) Medium

42. Which DC motor type maintains nearly constant speed?
(A) Series motor
(B) Universal motor
(C) Compound motor
(D) Shunt motor

43. The EMF induced in a DC generator depends on:
(A) Speed only
(B) Flux only
(C) Both speed and flux
(D) Load only

44. In a lead-acid battery, the electrolyte is:
(A) Sulfuric acid solution
(B) Hydrochloric acid
(C) Sodium hydroxide
(D) Distilled water

45. Which of the following is true for DC series motors?
(A) Speed varies greatly with load
(B) Speed remains constant
(C) Cannot start under load
(D) Requires no field winding

46. DC compound motors are used where:
(A) High starting torque and constant speed are needed
(B) Constant speed only
(C) Light loads only
(D) No torque required

47. In a DC shunt generator, the terminal voltage:
(A) Drops to zero
(B) Increases with load
(C) Decreases slightly with load
(D) Fluctuates randomly

48. The efficiency of a battery depends on:
(A) Type of casing
(B) Terminal voltage only
(C) Age only
(D) Load and internal resistance

49. A rechargeable battery can be used multiple times because:
(A) It stores more charge
(B) Chemical reactions are reversible
(C) It has low voltage
(D) It has high resistance

50. Which of the following increases the EMF of a DC generator?
(A) Increasing field current
(B) Decreasing speed
(C) Increasing load only
(D) Using smaller brushes