11. In a DC shunt generator, the field winding is connected—
A) In series with the armature
B) In parallel with the armature
C) In series with the load
D) Across commutator segments
✅ Answer: B
Explanation: In a shunt generator, field winding is connected across the armature (in parallel).
12. The terminal voltage of a DC generator is—
A) Equal to induced emf
B) Less than induced emf
C) More than induced emf
D) Zero when load is connected
✅ Answer: B
Explanation: Terminal voltage = Induced emf − Voltage drop in armature and brushes.
13. The armature reaction in DC generator causes—
A) Increase in main flux
B) Distortion and weakening of main flux
C) Strengthening of field flux
D) No effect on flux
✅ Answer: B
Explanation: Armature reaction distorts and weakens the main magnetic field.
14. The effect of armature reaction can be reduced by—
A) Increasing armature current
B) Decreasing field current
C) Using compensating winding
D) Decreasing speed
✅ Answer: C
Explanation: Compensating windings neutralize the effect of armature reaction.
15. The commutation process converts—
A) DC to AC
B) AC to DC
C) DC to pulsating DC
D) AC to pulsating DC
✅ Answer: B
Explanation: Commutation in a DC generator converts AC induced emf into unidirectional DC output.
16. Poor commutation results in—
A) Sparking at brushes
B) Reduced speed
C) Reduced emf
D) Increase in flux
✅ Answer: A
Explanation: Poor commutation causes sparking due to delayed current reversal.
17. Interpoles in a DC generator are used to—
A) Improve efficiency
B) Reduce armature reaction and improve commutation
C) Increase speed
D) Decrease field current
✅ Answer: B
Explanation: Interpoles provide a neutralizing flux that aids commutation.
18. The load characteristic of a DC shunt generator is—
A) Drooping
B) Rising
C) Flat
D) Constant
✅ Answer: A
Explanation: Due to voltage drop with load, the characteristic is slightly drooping.
19. In a DC series generator, the field winding carries—
A) Only armature current
B) Only field current
C) Load current
D) Shunt current
✅ Answer: C
Explanation: In a series generator, the same current flows through armature, field, and load.
20. For self-excitation in a DC generator, the condition is—
A) Residual magnetism + correct polarity + field resistance < critical resistance
B) Field resistance > critical resistance
C) No residual magnetism required
D) Field disconnected from armature
✅ Answer: A
Explanation: Self-excitation occurs if the field resistance is below critical value.
21. Critical field resistance is—
A) The minimum resistance for shunt field
B) The maximum resistance at which the generator just excites
C) Always constant
D) Independent of speed
✅ Answer: B
Explanation: It’s the maximum field resistance for which the generator can self-excite.
22. The open-circuit characteristic (OCC) of a DC generator is—
A) Straight line
B) Curved
C) Horizontal line
D) Hyperbolic
✅ Answer: B
Explanation: OCC is a nonlinear curve due to magnetic saturation.
23. In a DC generator, if the speed increases, the generated emf—
A) Increases
B) Decreases
C) Remains constant
D) First increases then decreases
✅ Answer: A
Explanation: , emf is directly proportional to speed.
24. The losses in a DC generator are—
A) Copper losses
B) Iron losses
C) Mechanical losses
D) All of the above
✅ Answer: D
Explanation: Total losses include copper, iron (core), and mechanical losses.
25. The efficiency of a DC generator is maximum when—
A) Variable losses = Constant losses
B) Copper loss = Iron loss
C) Field loss = Armature loss
D) Load current = Maximum
✅ Answer: A
Explanation: Efficiency is maximum when variable losses equal constant losses.
26. A cumulatively compounded DC generator gives—
A) Rising voltage with load
B) Falling voltage with load
C) Constant voltage
D) Zero voltage
✅ Answer: A
Explanation: Cumulative compounding strengthens the field with load current, improving voltage.
27. The brush contact drop per brush is approximately—
A) 0.2 V
B) 1–2 V
C) 5 V
D) 0.02 V
✅ Answer: B
Explanation: Typically around 1–2 V per brush depending on current and material.
28. The terminal voltage of a DC series generator—
A) Increases with load
B) Decreases with load
C) Remains constant
D) First increases then decreases
✅ Answer: D
Explanation: Initially increases due to more field current, but later drops due to armature reaction.
29. The magnetization curve of a DC generator is plotted between—
A) Field current and load current
B) Field current and generated emf
C) Speed and torque
D) Voltage and current
✅ Answer: B
Explanation: The magnetization curve shows the relation between field current and induced emf.
30. The main disadvantage of a DC series generator is—
A) Poor voltage regulation
B) High cost
C) High speed
D) Low current
✅ Answer: A
Explanation: Series generators have poor voltage regulation, so rarely used for power supply.
31. A differential compound generator is not used because—
A) It has unstable voltage
B) It is costly
C) It requires high speed
D) It gives low current
✅ Answer: A
Explanation: Differential compounding opposes main field, making voltage unstable.
32. The armature of a DC generator is—
A) Stationary
B) Rotating
C) Both stationary and rotating
D) None
✅ Answer: B
Explanation: Armature is the rotating part where emf is induced.
33. The field system of a DC generator is—
A) Stationary
B) Rotating
C) Commutating
D) Alternating
✅ Answer: A
Explanation: Field poles are stationary and mounted on the yoke.
34. The function of yoke in a DC machine is—
A) To provide mechanical support and magnetic path
B) To house armature winding
C) To act as a commutator
D) To carry brushes
✅ Answer: A
Explanation: The yoke provides mechanical strength and completes the magnetic circuit.
35. The material used for yoke is—
A) Cast iron or steel
B) Aluminum
C) Copper
D) Brass
✅ Answer: A
Explanation: Yoke is made of cast iron for small machines or cast steel for large ones.
36. The number of parallel paths in a wave-wound DC generator is—
A) Equal to number of poles
B) Always two
C) Equal to half of poles
D) Equal to twice the poles
✅ Answer: B
Explanation: In wave winding, number of parallel paths = 2, irrespective of poles.
37. In lap winding, the number of parallel paths is—
A) 2
B) Equal to number of poles
C) Half the number of poles
D) Double the number of poles
✅ Answer: B
Explanation: In lap winding, number of parallel paths = number of poles (A = P).
38. Wave winding is generally used for—
A) High current, low voltage generators
B) Low current, high voltage generators
C) Constant speed machines
D) Variable speed machines
✅ Answer: B
Explanation: Wave winding gives high voltage, low current output.
39. Lap winding is used for—
A) Low current, high voltage
B) High current, low voltage
C) High speed
D) None
✅ Answer: B
Explanation: Lap winding provides large current capacity due to more parallel paths.
40. The commutator segments are insulated by—
A) Mica
B) Paper
C) Plastic
D) Wood
✅ Answer: A
Explanation: Mica is used as insulation between commutator segments due to high dielectric strength.
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