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DC Generator MCQ Questions and Answers for Electrical Engineering Exams

August 07, 2021 , ,
DC Generator MCQ Questions and Answers for Electrical Engineering Exams

DC Generator MCQ Questions and Answers for Electrical Engineering Exams

Search Description: Practice 166 DC Generator MCQ questions with answers and short explanations for electrical engineering exams, diploma, ITI, SSC JE, RRB JE, GATE and technical interviews.

Post Updated: May 2026

This article contains 166 DC Generator MCQ questions with answers arranged from easy to hard level. These objective questions are useful for Electrical Engineering students, diploma students, ITI electrician trade, SSC JE Electrical, RRB JE, GATE basics, university exams and technical interview preparation.

Introduction to DC Generator MCQs

A DC generator is an electrical machine that converts mechanical energy into direct current electrical energy. It works on the principle of electromagnetic induction. Important topics from this chapter include construction of DC machines, armature winding, commutator, brushes, Fleming’s right-hand rule, generated EMF equation, armature reaction, commutation, types of DC generators and voltage characteristics.

The questions below are written in simple language so that beginners can revise the complete topic step by step. Each MCQ includes the correct answer and a short explanation, which helps in concept clarity instead of only memorizing the answer.

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Table of Contents

Quick Revision Notes on DC Generator

  • A DC generator converts mechanical energy into DC electrical energy.
  • It works on Faraday’s law of electromagnetic induction.
  • The armature core is laminated to reduce eddy current loss.
  • The commutator acts like a mechanical rectifier and gives DC output.
  • Brushes collect current from the commutator and deliver it to the external circuit.
  • Lap winding is suitable for low voltage and high current applications.
  • Wave winding is suitable for high voltage and low current applications.
  • Armature reaction distorts and weakens the main magnetic field.
  • Interpoles and compensating windings improve commutation and reduce sparking.

Easy Level DC Generator MCQ Questions

These questions cover basic construction, working principle and simple definitions of DC generators.

Question 1. Laminations of a DC machine core are generally made of:

  1. A. Cast iron
  2. B. Carbon
  3. C. Silicon steel
  4. D. Stainless steel

Answer: C. Silicon steel

Explanation: Silicon steel is used because it has good magnetic properties and helps reduce iron losses.

Question 2. The armature core of a DC generator is laminated mainly to reduce:

  1. A. Friction loss
  2. B. Eddy current loss
  3. C. Copper loss
  4. D. Brush contact loss

Answer: B. Eddy current loss

Explanation: Laminations break the path of circulating eddy currents and reduce heating in the core.

Question 3. The field coils of a DC generator are usually made of:

  1. A. Mica
  2. B. Copper
  3. C. Cast iron
  4. D. Carbon

Answer: B. Copper

Explanation: Copper has low resistance and high conductivity, so it is suitable for field windings.

Question 4. The commutator segments of a DC generator are usually insulated from each other by:

  1. A. Graphite
  2. B. Paper
  3. C. Mica
  4. D. Varnish only

Answer: C. Mica

Explanation: Mica is a strong insulating material used between copper commutator segments.

Question 5. A DC generator converts:

  1. A. Electrical energy into mechanical energy
  2. B. Mechanical energy into DC electrical energy
  3. C. DC energy into AC energy
  4. D. Heat energy into mechanical energy

Answer: B. Mechanical energy into DC electrical energy

Explanation: A DC generator takes mechanical input from a prime mover and gives DC electrical output.

Question 6. The working principle of a DC generator is based on:

  1. A. Ohm's law
  2. B. Faraday's law of electromagnetic induction
  3. C. Coulomb's law
  4. D. Kirchhoff's current law

Answer: B. Faraday's law of electromagnetic induction

Explanation: When a conductor cuts magnetic flux, an EMF is induced according to Faraday's law.

Question 7. Fleming’s right-hand rule is used to find the direction of:

  1. A. Motor force
  2. B. Induced EMF in a generator
  3. C. Magnetic leakage
  4. D. Armature resistance

Answer: B. Induced EMF in a generator

Explanation: For generator action, Fleming’s right-hand rule gives the direction of induced EMF/current.

Question 8. In Fleming’s right-hand rule, the forefinger represents:

  1. A. Direction of motion
  2. B. Direction of magnetic field
  3. C. Direction of induced current
  4. D. Direction of force

Answer: B. Direction of magnetic field

Explanation: The forefinger points in the direction of magnetic field or lines of force.

Question 9. In Fleming’s right-hand rule, the thumb represents:

  1. A. Magnetic field
  2. B. Induced current
  3. C. Motion of conductor
  4. D. Resistance direction

Answer: C. Motion of conductor

Explanation: The thumb indicates the direction of motion of the conductor.

Question 10. In Fleming’s right-hand rule, the middle finger represents:

  1. A. Magnetic field
  2. B. Induced current or EMF
  3. C. Motion of conductor
  4. D. Speed

Answer: B. Induced current or EMF

Explanation: The middle finger shows the direction of induced EMF/current.

Question 11. The function of the commutator in a DC generator is to:

  1. A. Increase speed
  2. B. Convert internally induced AC into DC at terminals
  3. C. Reduce field current to zero
  4. D. Cool the armature

Answer: B. Convert internally induced AC into DC at terminals

Explanation: The armature EMF is alternating internally, and the commutator rectifies it into DC output.

Question 12. Brushes in a DC generator collect current from the:

  1. A. Field poles
  2. B. Commutator
  3. C. Yoke
  4. D. Bearings

Answer: B. Commutator

Explanation: Brushes remain in contact with the commutator to transfer current to the external circuit.

Question 13. Brushes of DC machines are commonly made of:

  1. A. Carbon
  2. B. Glass
  3. C. Mica
  4. D. Cast iron

Answer: A. Carbon

Explanation: Carbon brushes provide good contact and reduce wear of the commutator.

Question 14. The outer frame of a DC machine is called the:

  1. A. Armature
  2. B. Yoke
  3. C. Commutator
  4. D. Brush holder

Answer: B. Yoke

Explanation: The yoke provides mechanical support and a path for magnetic flux.

Question 15. The rotating part of a DC generator is called the:

  1. A. Stator
  2. B. Armature
  3. C. Pole shoe
  4. D. Yoke

Answer: B. Armature

Explanation: In most DC machines, the armature rotates and EMF is induced in its conductors.

Question 16. The stationary field system of a DC generator produces:

  1. A. Mechanical torque only
  2. B. Main magnetic flux
  3. C. Brush pressure
  4. D. Eddy current

Answer: B. Main magnetic flux

Explanation: The field winding or magnets produce the main magnetic flux.

Question 17. Pole shoes in a DC generator help to:

  1. A. Increase armature resistance
  2. B. Spread magnetic flux uniformly
  3. C. Remove brushes
  4. D. Reduce shaft speed

Answer: B. Spread magnetic flux uniformly

Explanation: Pole shoes spread the flux over the armature surface and reduce magnetic reluctance.

Question 18. Bearings in a DC machine are used to support the:

  1. A. Field winding
  2. B. Rotor shaft
  3. C. Brushes only
  4. D. Commutator segments only

Answer: B. Rotor shaft

Explanation: Bearings allow smooth rotation of the shaft.

Question 19. A simple DC generator requires a prime mover to supply:

  1. A. Mechanical input power
  2. B. Field resistance
  3. C. Brush insulation
  4. D. Load resistance

Answer: A. Mechanical input power

Explanation: The prime mover rotates the armature or conductor system.

Question 20. The material generally used for commutator segments is:

  1. A. Copper
  2. B. Cast iron
  3. C. Porcelain
  4. D. Aluminium oxide

Answer: A. Copper

Explanation: Copper is used because of its high electrical conductivity.

Question 21. The induced EMF in a conductor moving in a magnetic field is proportional to:

  1. A. Flux density, length and velocity
  2. B. Only resistance
  3. C. Only temperature
  4. D. Only brush pressure

Answer: A. Flux density, length and velocity

Explanation: The basic relation is e = B l v for a straight conductor moving perpendicular to flux.

Question 22. In a four-pole DC machine, the poles are arranged as:

  1. A. All north poles
  2. B. All south poles
  3. C. Alternate north and south poles
  4. D. Two north poles followed by two south poles only

Answer: C. Alternate north and south poles

Explanation: Adjacent poles must be of opposite polarity to produce a useful magnetic field.

Question 23. The number of commutator segments is generally equal to the number of:

  1. A. Poles
  2. B. Armature coils
  3. C. Brushes
  4. D. Field turns

Answer: B. Armature coils

Explanation: Each armature coil is connected to commutator segments.

Question 24. The purpose of insulation in armature slots is to:

  1. A. Increase speed
  2. B. Prevent short circuit between conductors and core
  3. C. Increase friction
  4. D. Reduce terminal voltage

Answer: B. Prevent short circuit between conductors and core

Explanation: Slot insulation protects the winding from shorting to the armature core.

Question 25. A DC generator gives output through:

  1. A. Slip rings only
  2. B. Commutator and brushes
  3. C. Transformer winding
  4. D. Capacitor plates

Answer: B. Commutator and brushes

Explanation: The commutator-brush arrangement delivers DC output to the external circuit.

Question 26. The magnetic neutral axis is the axis where:

  1. A. Flux is maximum
  2. B. Generated EMF in the short-circuited coil is ideally zero
  3. C. Speed is zero
  4. D. Current is maximum

Answer: B. Generated EMF in the short-circuited coil is ideally zero

Explanation: Brushes are placed near the neutral axis to reduce sparking during commutation.

Question 27. On no-load, the armature current of a DC generator is approximately:

  1. A. Very large
  2. B. Zero or very small
  3. C. Equal to short-circuit current
  4. D. Infinite

Answer: B. Zero or very small

Explanation: With no external load, only a small current may flow for excitation depending on connection.

Question 28. A DC shunt generator has field winding connected:

  1. A. In series with armature
  2. B. In parallel with armature terminals
  3. C. Only through brushes
  4. D. Across the shaft

Answer: B. In parallel with armature terminals

Explanation: In a shunt generator, the field winding is connected across the generated voltage.

Question 29. A DC series generator has field winding connected:

  1. A. In parallel with load
  2. B. In series with armature and load
  3. C. Across the brushes only
  4. D. Not connected

Answer: B. In series with armature and load

Explanation: The series field carries the load current.

Question 30. A separately excited DC generator has field current supplied by:

  1. A. Its own armature only
  2. B. An external DC source
  3. C. The load only
  4. D. A capacitor only

Answer: B. An external DC source

Explanation: Its field winding is excited from a separate DC supply.

Question 31. The residual magnetism in a self-excited DC generator is needed for:

  1. A. Initial voltage build-up
  2. B. Reducing bearing friction
  3. C. Increasing brush size
  4. D. Cooling the yoke

Answer: A. Initial voltage build-up

Explanation: Residual magnetism produces a small initial EMF, which helps the generator build voltage.

Question 32. If there is no residual magnetism, a self-excited generator may:

  1. A. Build normal voltage instantly
  2. B. Fail to build up voltage
  3. C. Run as an alternator
  4. D. Give infinite voltage

Answer: B. Fail to build up voltage

Explanation: Without residual flux, initial EMF may be absent and voltage build-up may not start.

Question 33. Flashing the field of a DC generator means:

  1. A. Cleaning the commutator
  2. B. Restoring residual magnetism using a DC source
  3. C. Removing field winding
  4. D. Short-circuiting the armature

Answer: B. Restoring residual magnetism using a DC source

Explanation: Field flashing applies DC briefly to restore the correct residual magnetism.

Question 34. A common cause of rapid brush wear is:

  1. A. Smooth commutator only
  2. B. Severe sparking or rough commutator
  3. C. Low temperature only
  4. D. Correct brush grade

Answer: B. Severe sparking or rough commutator

Explanation: Sparking, rough surface, dust and wrong pressure can increase brush wear.

Question 35. The main purpose of ventilation in a DC machine is to:

  1. A. Increase voltage
  2. B. Remove heat
  3. C. Increase armature reaction
  4. D. Reduce flux to zero

Answer: B. Remove heat

Explanation: Ventilation helps maintain safe operating temperature.

Question 36. The core loss in a DC machine mainly includes:

  1. A. Hysteresis and eddy current losses
  2. B. Only brush loss
  3. C. Only copper loss
  4. D. Only friction loss

Answer: A. Hysteresis and eddy current losses

Explanation: Iron losses are due to magnetic reversal and eddy currents in the core.

Question 37. Mechanical losses in a DC machine mainly include:

  1. A. Friction and windage
  2. B. Armature copper loss
  3. C. Field copper loss
  4. D. Eddy current loss only

Answer: A. Friction and windage

Explanation: Bearing friction and air resistance are the main mechanical losses.

Question 38. Copper loss in armature winding is given by:

  1. A. Ia²Ra
  2. B. V/I
  3. C. B l v
  4. D. ΦZN/60

Answer: A. Ia²Ra

Explanation: Armature copper loss depends on the square of armature current and armature resistance.

Question 39. The terminal voltage of a DC generator is usually less than generated EMF because of:

  1. A. Armature resistance drop
  2. B. Zero armature current
  3. C. No magnetic field
  4. D. No commutator

Answer: A. Armature resistance drop

Explanation: Voltage drops occur due to armature resistance and other internal effects.

Question 40. The generated EMF of a DC generator is directly proportional to:

  1. A. Flux and speed
  2. B. Only brush pressure
  3. C. Only bearing size
  4. D. Only yoke weight

Answer: A. Flux and speed

Explanation: For a given machine, generated EMF is proportional to flux per pole and speed.

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Intermediate Level DC Generator MCQ Questions

These questions are useful for exam preparation because they cover winding, armature reaction, commutation, losses and generator characteristics.

Question 41. In a DC generator, the EMF equation is:

  1. A. E = PΦZN / 60A
  2. B. E = VI
  3. C. E = I²R
  4. D. E = B/H

Answer: A. E = PΦZN / 60A

Explanation: The standard generated EMF equation is E = PΦZN / 60A.

Question 42. In the DC generator EMF equation, A represents:

  1. A. Number of poles
  2. B. Number of parallel paths
  3. C. Armature resistance
  4. D. Air-gap length

Answer: B. Number of parallel paths

Explanation: A is the number of parallel paths in the armature winding.

Question 43. For simplex lap winding, the number of parallel paths is equal to:

  1. A. 2
  2. B. Number of poles
  3. C. Half the number of poles
  4. D. Number of slots only

Answer: B. Number of poles

Explanation: In simplex lap winding, A = P.

Question 44. For simplex wave winding, the number of parallel paths is:

  1. A. 2
  2. B. Number of poles
  3. C. Number of commutator bars
  4. D. Zero

Answer: A. 2

Explanation: In simplex wave winding, A = 2, independent of number of poles.

Question 45. Lap winding is generally preferred for:

  1. A. High voltage, low current
  2. B. Low voltage, high current
  3. C. Only AC machines
  4. D. No-load operation only

Answer: B. Low voltage, high current

Explanation: Lap winding provides many parallel paths, so it is suitable for high current and low voltage.

Question 46. Wave winding is generally preferred for:

  1. A. Low voltage, high current
  2. B. High voltage, low current
  3. C. Only welding machines
  4. D. Only transformers

Answer: B. High voltage, low current

Explanation: Wave winding has fewer parallel paths and gives higher voltage for the same conductors.

Question 47. Equalizer rings are mainly used in:

  1. A. Wave-wound armatures
  2. B. Lap-wound armatures
  3. C. Transformers
  4. D. Induction motors

Answer: B. Lap-wound armatures

Explanation: Equalizer rings reduce circulating currents caused by unequal induced EMFs in parallel paths.

Question 48. In lap winding, the number of brushes is generally:

  1. A. Two only
  2. B. Equal to the number of poles
  3. C. Equal to number of slots
  4. D. Zero

Answer: B. Equal to the number of poles

Explanation: A lap-wound machine normally has as many brush sets as poles.

Question 49. A welding generator usually requires:

  1. A. High voltage and low current
  2. B. Low voltage and high current
  3. C. No current
  4. D. Only AC output

Answer: B. Low voltage and high current

Explanation: Welding needs high current at relatively low voltage, so lap winding is suitable.

Question 50. The resultant pitch in lap winding is usually the:

  1. A. Sum of front and back pitch
  2. B. Difference of back and front pitch
  3. C. Product of pitches
  4. D. Ratio of pole pitch to speed

Answer: B. Difference of back and front pitch

Explanation: In lap winding, resultant pitch is the algebraic difference between back and front pitches.

Question 51. A fractional pitch winding in a DC machine helps to:

  1. A. Reduce copper in end connections and improve commutation
  2. B. Increase core loss
  3. C. Remove commutator
  4. D. Increase brush wear

Answer: A. Reduce copper in end connections and improve commutation

Explanation: Short-pitch winding can save copper and may reduce sparking.

Question 52. Armature reaction in a DC generator is the effect of:

  1. A. Brush friction on commutator
  2. B. Armature current magnetic field on main field
  3. C. Bearing friction on shaft
  4. D. Yoke weight on speed

Answer: B. Armature current magnetic field on main field

Explanation: The magnetic field produced by armature current distorts and weakens the main field.

Question 53. The armature reaction of an unsaturated DC machine is mainly:

  1. A. Cross-magnetizing
  2. B. Only heating
  3. C. Only mechanical
  4. D. Only cooling

Answer: A. Cross-magnetizing

Explanation: In an unsaturated machine, the main effect is cross-magnetization or flux distortion.

Question 54. The demagnetizing component of armature reaction causes:

  1. A. Increase in generated voltage
  2. B. Reduction in generated EMF
  3. C. Increase in speed only
  4. D. No change

Answer: B. Reduction in generated EMF

Explanation: Demagnetization weakens the main flux and reduces generated EMF.

Question 55. Compensating windings are used to:

  1. A. Neutralize armature reaction under pole faces
  2. B. Increase bearing friction
  3. C. Reduce copper conductivity
  4. D. Replace the commutator

Answer: A. Neutralize armature reaction under pole faces

Explanation: Compensating windings oppose the cross-magnetizing armature flux.

Question 56. Interpoles are connected in series with:

  1. A. Field rheostat only
  2. B. Armature winding
  3. C. Load only in shunt
  4. D. Yoke

Answer: B. Armature winding

Explanation: Interpoles carry armature current so their effect changes with load.

Question 57. The main function of interpoles is to:

  1. A. Improve commutation
  2. B. Increase shaft length
  3. C. Reduce field resistance to zero
  4. D. Remove ventilation

Answer: A. Improve commutation

Explanation: Interpoles induce a reversing EMF to help current reversal during commutation.

Question 58. For sparkless commutation, brushes are generally placed near:

  1. A. Geometrical neutral axis only at all loads
  2. B. Magnetic neutral axis
  3. C. Field pole center
  4. D. Shaft center

Answer: B. Magnetic neutral axis

Explanation: The coil under commutation should have minimum induced EMF, so brushes are placed at MNA.

Question 59. If a DC generator brush is shifted too much, it may cause:

  1. A. Better insulation always
  2. B. Sparking and demagnetization
  3. C. No effect
  4. D. Zero mechanical loss

Answer: B. Sparking and demagnetization

Explanation: Incorrect brush position can worsen commutation and reduce main flux.

Question 60. The armature coil is short-circuited by a brush when it lies near the:

  1. A. Field axis
  2. B. Neutral axis
  3. C. Shaft axis only
  4. D. Pole center

Answer: B. Neutral axis

Explanation: During commutation, the coil under the brush is short-circuited near the neutral plane.

Question 61. Commutation is the process of:

  1. A. Changing AC armature output into DC at terminals
  2. B. Changing DC into mechanical power only
  3. C. Increasing load resistance
  4. D. Cooling windings

Answer: A. Changing AC armature output into DC at terminals

Explanation: Commutation reverses coil current at the proper instant and gives unidirectional external current.

Question 62. A large number of commutator segments helps to:

  1. A. Increase ripple in output
  2. B. Reduce ripple in generated DC
  3. C. Stop rotation
  4. D. Increase brush sparking

Answer: B. Reduce ripple in generated DC

Explanation: More segments make the output smoother and reduce ripple.

Question 63. High mica between commutator bars can cause:

  1. A. Smooth running always
  2. B. Brush jumping and sparking
  3. C. Zero loss
  4. D. Higher efficiency always

Answer: B. Brush jumping and sparking

Explanation: If mica is not undercut properly, brushes may not make smooth contact.

Question 64. Undercutting of mica in commutator is done to:

  1. A. Allow brushes to contact copper segments properly
  2. B. Increase mica height
  3. C. Stop current collection
  4. D. Increase sparking

Answer: A. Allow brushes to contact copper segments properly

Explanation: Mica is undercut because it is harder than copper and can disturb brush contact.

Question 65. The polarity of interpoles in a DC generator is usually:

  1. A. Same as the main pole ahead in direction of rotation
  2. B. Opposite to all poles
  3. C. Always neutral
  4. D. Same as previous pole only for motors

Answer: A. Same as the main pole ahead in direction of rotation

Explanation: For generators, interpole polarity is the same as the next main pole in the direction of rotation.

Question 66. Open-circuited armature coil may be indicated by:

  1. A. No mark anywhere
  2. B. Sparking and scarring at related commutator segment
  3. C. Only low bearing noise
  4. D. Higher field current always

Answer: B. Sparking and scarring at related commutator segment

Explanation: An open coil can cause sparking and damage at the corresponding commutator segment.

Question 67. Short circuit in armature winding may be caused by:

  1. A. Insulation failure between commutator bars
  2. B. Turn-to-turn insulation failure
  3. C. Ground fault in coil turns
  4. D. All of the above

Answer: D. All of the above

Explanation: All these faults can create unwanted short-circuit paths.

Question 68. A short-circuited field coil may cause:

  1. A. Burning smell
  2. B. Unbalanced magnetic pull
  3. C. Reduced generated voltage
  4. D. All of the above

Answer: D. All of the above

Explanation: Shorted field turns reduce field strength and may produce heating and vibration.

Question 69. The voltage build-up of a DC shunt generator depends on:

  1. A. Residual magnetism
  2. B. Correct field connection
  3. C. Field resistance below critical value
  4. D. All of the above

Answer: D. All of the above

Explanation: All these conditions are required for successful self-excitation.

Question 70. Critical resistance of a DC shunt generator refers to:

  1. A. Maximum field circuit resistance for voltage build-up at a given speed
  2. B. Armature short-circuit resistance
  3. C. Brush resistance only
  4. D. Load resistance only

Answer: A. Maximum field circuit resistance for voltage build-up at a given speed

Explanation: If field resistance is above critical value, the generator may not build up voltage.

Question 71. Critical speed of a DC shunt generator is the speed:

  1. A. Below which generator fails to build up for given field resistance
  2. B. At which shaft breaks
  3. C. At which load is zero
  4. D. At which brushes melt

Answer: A. Below which generator fails to build up for given field resistance

Explanation: For a given field resistance, the machine needs minimum speed to build voltage.

Question 72. Increasing the speed of a DC shunt generator generally:

  1. A. Decreases critical resistance
  2. B. Increases critical resistance
  3. C. Makes field resistance zero
  4. D. Removes residual magnetism

Answer: B. Increases critical resistance

Explanation: Higher speed increases the slope of OCC, so critical resistance increases.

Question 73. If the field resistance of a shunt generator is increased too much, terminal voltage:

  1. A. Increases without limit
  2. B. Decreases and may fail to build up
  3. C. Becomes AC
  4. D. Becomes independent of speed

Answer: B. Decreases and may fail to build up

Explanation: Higher field resistance reduces field current and generated voltage.

Question 74. The open-circuit characteristic of a DC generator is also called:

  1. A. Magnetization characteristic
  2. B. Load characteristic
  3. C. External resistance curve only
  4. D. Efficiency curve

Answer: A. Magnetization characteristic

Explanation: OCC shows generated EMF versus field current at constant speed.

Question 75. The external characteristic of a DC generator shows relation between:

  1. A. Terminal voltage and load current
  2. B. Field current and speed only
  3. C. Flux and pole pitch only
  4. D. Brush pressure and voltage

Answer: A. Terminal voltage and load current

Explanation: It describes how terminal voltage changes with load current.

Question 76. Internal characteristic of a DC generator gives relation between:

  1. A. Generated EMF and armature current
  2. B. Shaft diameter and speed
  3. C. Bearing loss and field current
  4. D. Mica thickness and voltage

Answer: A. Generated EMF and armature current

Explanation: Internal characteristic includes the effect of armature reaction but not armature resistance drop.

Question 77. In a DC shunt generator, terminal voltage drops with load because of:

  1. A. Armature resistance drop
  2. B. Armature reaction
  3. C. Reduced field current due to lower terminal voltage
  4. D. All of the above

Answer: D. All of the above

Explanation: All these effects contribute to voltage drop under load.

Question 78. A series generator has nearly zero terminal voltage at no-load because:

  1. A. No load current means no series field current
  2. B. Brushes are absent
  3. C. Armature cannot rotate
  4. D. Commutator is open

Answer: A. No load current means no series field current

Explanation: Without load current, series field flux is very small except residual flux.

Question 79. A DC series generator is commonly used as:

  1. A. Feeder booster
  2. B. Constant-voltage laboratory supply
  3. C. Transformer
  4. D. AC alternator

Answer: A. Feeder booster

Explanation: Series generators can compensate voltage drop in DC feeders.

Question 80. A shunt generator is commonly preferred for:

  1. A. Battery charging and general DC supply
  2. B. Only welding at very high current
  3. C. Only no-load testing
  4. D. Only AC transmission

Answer: A. Battery charging and general DC supply

Explanation: Shunt generators provide comparatively stable voltage for many DC applications.

Question 81. An over-compounded generator has full-load terminal voltage:

  1. A. Less than no-load voltage
  2. B. Equal to no-load voltage
  3. C. Greater than no-load voltage
  4. D. Always zero

Answer: C. Greater than no-load voltage

Explanation: Series field overcompensates voltage drops, so full-load voltage becomes higher.

Question 82. A flat-compounded or level-compounded generator gives full-load terminal voltage:

  1. A. Almost equal to no-load voltage
  2. B. Always zero
  3. C. Much lower than no-load voltage
  4. D. Only AC

Answer: A. Almost equal to no-load voltage

Explanation: It compensates internal drops so terminal voltage remains nearly constant.

Question 83. A differentially compounded generator has series field flux:

  1. A. Aiding shunt field flux
  2. B. Opposing shunt field flux
  3. C. Zero at all loads
  4. D. Independent of current

Answer: B. Opposing shunt field flux

Explanation: Differential compounding weakens total flux as load increases.

Question 84. For charging batteries, the generator voltage must be:

  1. A. Slightly higher than battery voltage
  2. B. Always zero
  3. C. Much lower than battery voltage
  4. D. AC only

Answer: A. Slightly higher than battery voltage

Explanation: Current flows into the battery only when generator voltage exceeds battery terminal voltage.

Question 85. The terminal voltage of a separately excited generator can be controlled mainly by changing:

  1. A. Field current
  2. B. Bearing type
  3. C. Brush material only
  4. D. Yoke thickness only

Answer: A. Field current

Explanation: Changing field current changes flux and therefore generated EMF.

Question 86. In a DC generator, if speed doubles and flux remains constant, generated EMF:

  1. A. Halves
  2. B. Doubles
  3. C. Becomes zero
  4. D. Remains unchanged

Answer: B. Doubles

Explanation: Generated EMF is directly proportional to speed when flux is constant.

Question 87. A 200 V DC generator running at 1000 rpm will generate nearly what voltage at 1200 rpm if flux is constant?

  1. A. 167 V
  2. B. 200 V
  3. C. 240 V
  4. D. 400 V

Answer: C. 240 V

Explanation: Voltage is proportional to speed: 200 × 1200/1000 = 240 V.

Question 88. If generated EMF is 600 V, armature current is 200 A and armature resistance is 0.1 Ω, terminal voltage is:

  1. A. 620 V
  2. B. 600 V
  3. C. 580 V
  4. D. 560 V

Answer: C. 580 V

Explanation: For a generator, V = E - IaRa = 600 - 200×0.1 = 580 V.

Question 89. If B = 0.8 T, l = 0.5 m and v = 10 m/s, induced EMF in one conductor is:

  1. A. 0.4 V
  2. B. 4 V
  3. C. 40 V
  4. D. 400 V

Answer: B. 4 V

Explanation: e = B l v = 0.8 × 0.5 × 10 = 4 V.

Question 90. A 4-pole simplex lap-wound DC generator has how many parallel paths?

  1. A. 2
  2. B. 4
  3. C. 6
  4. D. 8

Answer: B. 4

Explanation: For simplex lap winding, A = P = 4.

Question 91. A 6-pole simplex wave-wound DC generator has how many parallel paths?

  1. A. 2
  2. B. 4
  3. C. 6
  4. D. 12

Answer: A. 2

Explanation: For simplex wave winding, A = 2.

Question 92. For the same poles, flux, conductors and speed, wave winding gives higher voltage than lap winding because:

  1. A. It has fewer parallel paths
  2. B. It has more brushes only
  3. C. It has no commutator
  4. D. It has zero resistance

Answer: A. It has fewer parallel paths

Explanation: Generated EMF is inversely proportional to number of parallel paths A.

Question 93. For the same machine, a lap winding gives higher current capacity because:

  1. A. It has more parallel paths
  2. B. It has no magnetic field
  3. C. It has fewer conductors
  4. D. It removes copper loss

Answer: A. It has more parallel paths

Explanation: More parallel paths share armature current, improving current capacity.

Question 94. Stray loss in a DC machine is commonly taken as the sum of:

  1. A. Iron loss and mechanical loss
  2. B. Copper loss and brush loss only
  3. C. Load loss and field loss only
  4. D. Input and output

Answer: A. Iron loss and mechanical loss

Explanation: Stray/constant losses often include iron, friction and windage losses.

Question 95. Iron losses in a DC generator are mainly affected by:

  1. A. Speed and flux density
  2. B. Load current only
  3. C. Brush pressure only
  4. D. Bearing color

Answer: A. Speed and flux density

Explanation: Hysteresis and eddy current losses depend on magnetic flux and speed/frequency of reversal.

Question 96. Mechanical losses are mainly a function of:

  1. A. Speed
  2. B. Load current only
  3. C. Field resistance only
  4. D. Commutator mica

Answer: A. Speed

Explanation: Friction and windage usually increase with speed.

Question 97. The efficiency of a DC generator is maximum when:

  1. A. Variable copper loss equals constant loss
  2. B. Input is zero
  3. C. Load is zero
  4. D. Armature resistance is infinite

Answer: A. Variable copper loss equals constant loss

Explanation: Maximum efficiency condition is variable loss = constant loss.

Question 98. Voltage regulation of a DC generator is preferred to be:

  1. A. As low as possible
  2. B. Infinite
  3. C. 100% always
  4. D. Negative always

Answer: A. As low as possible

Explanation: Low regulation means terminal voltage changes less with load.

Question 99. A DC generator can be considered as a:

  1. A. Rotating energy converter
  2. B. Static transformer only
  3. C. Pure resistor
  4. D. Battery only

Answer: A. Rotating energy converter

Explanation: It converts mechanical energy into electrical energy through rotation and electromagnetic induction.

Question 100. The armature is the part of a machine where:

  1. A. Useful EMF is induced
  2. B. Only field winding is placed
  3. C. Only bearings are fixed
  4. D. No current can flow

Answer: A. Useful EMF is induced

Explanation: The armature houses the conductors in which useful EMF is generated.

Question 101. In a DC generator, brushes are placed on the commutator in the:

  1. A. Inter-polar region
  2. B. Center of pole face only
  3. C. Yoke surface
  4. D. Bearing housing

Answer: A. Inter-polar region

Explanation: Brushes are placed near the neutral region for better commutation.

Question 102. The main reason for using carbon brushes instead of copper brushes in many DC machines is:

  1. A. Better commutation and less commutator wear
  2. B. Higher weight
  3. C. No contact resistance
  4. D. To increase sparking

Answer: A. Better commutation and less commutator wear

Explanation: Carbon brushes are softer and provide better commutation characteristics.

Question 103. Copper brushes are preferred where:

  1. A. Low voltage and high current are involved
  2. B. High voltage and very small current are involved
  3. C. No current flows
  4. D. Only AC supply is used

Answer: A. Low voltage and high current are involved

Explanation: Copper/metal graphite brushes have lower contact drop and suit heavy current applications.

Question 104. Metal graphite brushes generally have:

  1. A. Lower contact voltage drop
  2. B. Infinite resistance
  3. C. No current carrying capacity
  4. D. No mechanical contact

Answer: A. Lower contact voltage drop

Explanation: Metal graphite brushes are used where low voltage drop and high current capacity are needed.

Question 105. A rough commutator surface may cause:

  1. A. Rapid brush wear
  2. B. Perfect no-loss operation
  3. C. Zero sparking always
  4. D. No heating

Answer: A. Rapid brush wear

Explanation: Rough surface increases friction and can cause sparking and brush damage.

Question 106. The air-gap flux distribution on no-load in a practical DC machine is often:

  1. A. Approximately flat-topped under pole arc
  2. B. Always square wave of current
  3. C. Zero everywhere
  4. D. Triangular only

Answer: A. Approximately flat-topped under pole arc

Explanation: Pole shoes are shaped to give a fairly uniform flux under the pole face.

Question 107. The actual flux distribution in a DC generator depends on:

  1. A. Air gap length
  2. B. Pole shoe shape
  3. C. Spacing between pole tips
  4. D. All of the above

Answer: D. All of the above

Explanation: Machine geometry strongly affects the air-gap flux pattern.

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Hard Level DC Generator MCQ Questions

These questions include numerical problems, parallel operation, compounding, voltage build-up and advanced concepts.

Question 108. A 4-pole DC generator has 480 conductors, flux per pole 0.02 Wb, speed 1000 rpm and wave winding. Generated EMF is:

  1. A. 160 V
  2. B. 320 V
  3. C. 640 V
  4. D. 960 V

Answer: B. 320 V

Explanation: E = PΦZN/60A = 4×0.02×480×1000/(60×2) = 320 V.

Question 109. A 6-pole lap-wound generator has 600 conductors, flux per pole 0.03 Wb and speed 900 rpm. Generated EMF is:

  1. A. 270 V
  2. B. 450 V
  3. C. 900 V
  4. D. 1620 V

Answer: A. 270 V

Explanation: For lap winding A=P=6, so E = 6×0.03×600×900/(60×6)=270 V.

Question 110. A 4-pole wave-wound generator must generate 500 V at 1000 rpm with flux 0.025 Wb. Approximate number of conductors required is:

  1. A. 300
  2. B. 600
  3. C. 1200
  4. D. 1500

Answer: B. 600

Explanation: Z = 60AE/(PΦN)=60×2×500/(4×0.025×1000)=600 conductors.

Question 111. If a 250 V generator has armature resistance 0.05 Ω and supplies 100 A, generated EMF neglecting brush drop is:

  1. A. 245 V
  2. B. 250 V
  3. C. 255 V
  4. D. 300 V

Answer: C. 255 V

Explanation: For generator, E = V + IaRa = 250 + 100×0.05 = 255 V.

Question 112. A DC generator has generated EMF 240 V and terminal voltage 230 V at 50 A. Armature resistance is:

  1. A. 0.1 Ω
  2. B. 0.2 Ω
  3. C. 2 Ω
  4. D. 10 Ω

Answer: B. 0.2 Ω

Explanation: Ra = (E - V)/Ia = (240 - 230)/50 = 0.2 Ω.

Question 113. If a shunt generator terminal voltage is 220 V and shunt field resistance is 110 Ω, field current is:

  1. A. 1 A
  2. B. 2 A
  3. C. 5 A
  4. D. 10 A

Answer: B. 2 A

Explanation: Ish = V/Rsh = 220/110 = 2 A.

Question 114. A shunt generator supplies 100 A load at 220 V and has shunt field current 2 A. Armature current is:

  1. A. 98 A
  2. B. 100 A
  3. C. 102 A
  4. D. 220 A

Answer: C. 102 A

Explanation: In a shunt generator, Ia = IL + Ish = 100 + 2 = 102 A.

Question 115. A long-shunt compound generator has load current 80 A and shunt field current 2 A. Series field current is approximately:

  1. A. 2 A
  2. B. 78 A
  3. C. 80 A
  4. D. 82 A

Answer: C. 80 A

Explanation: In long-shunt connection, the series field carries load current.

Question 116. A short-shunt compound generator has load current 80 A and shunt field current 2 A. Armature current is:

  1. A. 78 A
  2. B. 80 A
  3. C. 82 A
  4. D. 160 A

Answer: C. 82 A

Explanation: In short-shunt connection, Ia = IL + Ish = 82 A.

Question 117. If a DC generator has constant losses of 500 W, maximum efficiency occurs when armature copper loss is:

  1. A. 0 W
  2. B. 250 W
  3. C. 500 W
  4. D. 1000 W

Answer: C. 500 W

Explanation: Maximum efficiency occurs when variable copper loss equals constant loss.

Question 118. A generator delivers 10 kW and has total losses 1 kW. Efficiency is:

  1. A. 90.9%
  2. B. 91.5%
  3. C. 95%
  4. D. 99%

Answer: A. 90.9%

Explanation: Efficiency = output/(output + losses) = 10/(10+1)=90.9%.

Question 119. A generator has output 20 kW at 250 V. Load current is:

  1. A. 40 A
  2. B. 60 A
  3. C. 80 A
  4. D. 100 A

Answer: C. 80 A

Explanation: I = P/V = 20000/250 = 80 A.

Question 120. A 250 V DC shunt generator has armature resistance 0.1 Ω and armature current 100 A. Generated EMF is:

  1. A. 240 V
  2. B. 250 V
  3. C. 260 V
  4. D. 350 V

Answer: C. 260 V

Explanation: E = V + IaRa = 250 + 10 = 260 V.

Question 121. A 220 V generator has brush drop of 2 V total and armature drop of 10 V. Generated EMF is:

  1. A. 208 V
  2. B. 220 V
  3. C. 232 V
  4. D. 242 V

Answer: C. 232 V

Explanation: E = V + armature drop + brush drop = 220 + 10 + 2 = 232 V.

Question 122. For two identical shunt generators in parallel, stable load sharing is helped by:

  1. A. Drooping voltage characteristics
  2. B. Rising voltage characteristics only
  3. C. Zero armature resistance
  4. D. No field winding

Answer: A. Drooping voltage characteristics

Explanation: Drooping characteristics allow load current to be shared more stably.

Question 123. If two DC generators are connected in parallel, the incoming generator should have:

  1. A. Same polarity and nearly same voltage as busbar
  2. B. Opposite polarity
  3. C. Zero voltage
  4. D. Only higher frequency

Answer: A. Same polarity and nearly same voltage as busbar

Explanation: Matching polarity and voltage prevents heavy circulating current.

Question 124. Before connecting a DC generator to busbars, it is brought to floating condition to:

  1. A. Avoid sudden current and mechanical shock
  2. B. Increase brush wear
  3. C. Remove field excitation
  4. D. Short the load

Answer: A. Avoid sudden current and mechanical shock

Explanation: Floating condition means its voltage matches busbar voltage with no large current flow.

Question 125. An equalizer connection in compound generators is used to:

  1. A. Improve load sharing and prevent reversal of series field effect
  2. B. Increase speed only
  3. C. Remove shunt field
  4. D. Increase brush drop

Answer: A. Improve load sharing and prevent reversal of series field effect

Explanation: Equalizer bars help compound generators share current properly during parallel operation.

Question 126. A generator may start motoring during parallel operation if:

  1. A. Its generated EMF becomes lower than busbar voltage
  2. B. Its voltage is much higher than busbar
  3. C. Its field is very strong always
  4. D. Its speed is too high always

Answer: A. Its generated EMF becomes lower than busbar voltage

Explanation: If generated EMF falls below bus voltage, current can enter the machine and it may act as a motor.

Question 127. In a DC generator, armature reaction causes the magnetic neutral axis to shift:

  1. A. In the direction of rotation
  2. B. Opposite to direction of rotation
  3. C. Not at all under any load
  4. D. To the shaft center

Answer: A. In the direction of rotation

Explanation: For a generator, MNA shifts in the direction of rotation.

Question 128. To reduce sparking in a generator without interpoles, brushes are shifted:

  1. A. Forward in direction of rotation
  2. B. Backward against rotation
  3. C. To pole center
  4. D. Removed completely

Answer: A. Forward in direction of rotation

Explanation: Generator brushes are usually rocked forward to align with the shifted MNA.

Question 129. Armature reaction at leading pole tip and trailing pole tip in a generator causes:

  1. A. Demagnetization at leading tip and magnetization at trailing tip
  2. B. Magnetization at leading tip and demagnetization at trailing tip
  3. C. No distortion
  4. D. Only mechanical vibration

Answer: A. Demagnetization at leading tip and magnetization at trailing tip

Explanation: In generator action, flux weakens at the leading pole tip and strengthens at the trailing pole tip.

Question 130. The purpose of dummy coils in DC armature winding is to:

  1. A. Provide mechanical balance
  2. B. Increase generated voltage directly
  3. C. Reduce field resistance
  4. D. Act as commutator insulation

Answer: A. Provide mechanical balance

Explanation: Dummy coils are not electrically active; they provide mechanical balance in slots.

Question 131. If residual magnetism exists but field connections oppose it, the generator will:

  1. A. Build up normally
  2. B. Fail to build or build in wrong direction
  3. C. Have zero friction
  4. D. Produce AC only

Answer: B. Fail to build or build in wrong direction

Explanation: Wrong field connection weakens residual flux instead of strengthening it.

Question 132. The first action when a self-excited generator fails to build up after installation is often to:

  1. A. Check/reverse field connections if needed
  2. B. Increase load current heavily
  3. C. Short the commutator
  4. D. Remove brushes

Answer: A. Check/reverse field connections if needed

Explanation: Incorrect field polarity is a common reason for failure to build voltage.

Question 133. In a shunt generator, voltage build-up is restricted at high field current mainly due to:

  1. A. Magnetic saturation
  2. B. Zero speed
  3. C. Open armature
  4. D. No brush contact

Answer: A. Magnetic saturation

Explanation: After saturation, large increases in field current produce only small voltage increase.

Question 134. A 220 V generator running at full speed without excitation may show a small voltage because of:

  1. A. Residual magnetism
  2. B. Full-load current
  3. C. High load resistance
  4. D. Series field current

Answer: A. Residual magnetism

Explanation: Residual magnetism can induce a small open-circuit voltage even without external excitation.

Question 135. At zero speed, residual magnetism in a DC generator produces induced EMF of:

  1. A. Zero
  2. B. Rated voltage
  3. C. Very high voltage
  4. D. Half rated voltage

Answer: A. Zero

Explanation: EMF requires conductor motion relative to flux; at zero speed, EMF is zero.

Question 136. If field winding of an energized DC shunt generator is suddenly opened, dangerous voltage may appear because:

  1. A. Field winding has inductance
  2. B. Armature has no resistance
  3. C. Commutator is copper
  4. D. Brushes are carbon

Answer: A. Field winding has inductance

Explanation: Opening an inductive field circuit can produce a high voltage spike.

Question 137. A DC series generator can self-excite only when:

  1. A. Load current flows
  2. B. Load current is zero
  3. C. Field is disconnected
  4. D. Speed is zero

Answer: A. Load current flows

Explanation: Series field current depends on load current.

Question 138. For long DC feeders, an over-compound generator is preferred because it:

  1. A. Compensates feeder voltage drop
  2. B. Gives zero voltage at full load
  3. C. Removes line current
  4. D. Works without field

Answer: A. Compensates feeder voltage drop

Explanation: Its terminal voltage rises with load to offset line voltage drop.

Question 139. The external characteristic of a DC series generator initially rises because:

  1. A. Flux increases with load current
  2. B. Armature resistance becomes zero
  3. C. Speed increases infinitely
  4. D. Brush drop disappears

Answer: A. Flux increases with load current

Explanation: More load current strengthens series field flux until saturation.

Question 140. After magnetic saturation, the terminal voltage of a series generator may fall due to:

  1. A. Armature and series field resistance drops
  2. B. Flux increasing infinitely
  3. C. Zero current
  4. D. No losses

Answer: A. Armature and series field resistance drops

Explanation: At high current, resistance drops dominate and voltage may decrease.

Question 141. In a DC generator, the load current in a shunt generator is:

  1. A. Ia - Ish
  2. B. Ia + Ish
  3. C. Only field current
  4. D. Always zero

Answer: A. Ia - Ish

Explanation: Armature current splits into load current and shunt field current, so IL = Ia - Ish.

Question 142. In a series generator:

  1. A. Ia = Ise = IL
  2. B. Ia = Ish only
  3. C. IL = 0 always
  4. D. Field current is independent of load

Answer: A. Ia = Ise = IL

Explanation: Armature, series field and load are in series.

Question 143. For a compound generator, full-load terminal voltage may be greater, equal or less than no-load voltage depending on:

  1. A. Degree of compounding
  2. B. Bearing size
  3. C. Brush color
  4. D. Number of cooling fans only

Answer: A. Degree of compounding

Explanation: Over, level and under compounding decide the load-voltage behavior.

Question 144. Which generator is most suitable where terminal voltage should remain nearly constant from no-load to full-load?

  1. A. Level-compounded generator
  2. B. Series generator only
  3. C. Differential compound generator
  4. D. Unexcited generator

Answer: A. Level-compounded generator

Explanation: Level compounding compensates internal voltage drops at full load.

Question 145. A differentially compounded generator is generally unsuitable for stable DC supply because:

  1. A. Voltage falls sharply with load
  2. B. Voltage is perfectly constant
  3. C. It has no field
  4. D. It cannot rotate

Answer: A. Voltage falls sharply with load

Explanation: Opposing series field weakens flux as load increases.

Question 146. A separately excited generator gives better voltage control because:

  1. A. Field current is independent of load current
  2. B. It has no armature
  3. C. It has no losses
  4. D. It has no commutator

Answer: A. Field current is independent of load current

Explanation: External field supply allows independent adjustment of excitation.

Question 147. The voltage drop across carbon brushes is usually treated as:

  1. A. Approximately constant over normal current range
  2. B. Exactly zero
  3. C. Infinite
  4. D. Equal to armature current squared

Answer: A. Approximately constant over normal current range

Explanation: Brush contact drop is often approximated as nearly constant.

Question 148. If commutation is poor, the most visible symptom is:

  1. A. Sparking at brushes
  2. B. No shaft rotation only
  3. C. No magnetic field in yoke
  4. D. Zero field resistance

Answer: A. Sparking at brushes

Explanation: Poor current reversal causes sparking at the commutator-brush contact.

Question 149. Reactance voltage during commutation is due to:

  1. A. Self-inductance of the short-circuited coil
  2. B. Bearing friction
  3. C. Yoke reluctance only
  4. D. Brush spring color

Answer: A. Self-inductance of the short-circuited coil

Explanation: The coil undergoing commutation has inductance, which opposes current reversal.

Question 150. Interpoles help neutralize:

  1. A. Reactance voltage and local armature reaction in commutating zone
  2. B. Bearing loss only
  3. C. Windage loss only
  4. D. Field copper loss only

Answer: A. Reactance voltage and local armature reaction in commutating zone

Explanation: Interpoles improve commutation by producing a suitable local reversing EMF.

Question 151. Compensating winding is placed in:

  1. A. Pole shoes
  2. B. Armature shaft
  3. C. Bearings
  4. D. Brush holders

Answer: A. Pole shoes

Explanation: It is embedded in pole faces to counter armature reaction under the poles.

Question 152. Compensating winding is generally connected:

  1. A. In series with armature
  2. B. In parallel with shunt field
  3. C. Across load only
  4. D. Open circuited

Answer: A. In series with armature

Explanation: It must carry armature current to cancel armature reaction proportional to load.

Question 153. The leakage flux in a DC generator is flux that:

  1. A. Does not link with armature conductors usefully
  2. B. Produces full output voltage
  3. C. Only exists in brushes
  4. D. Has zero magnetic path

Answer: A. Does not link with armature conductors usefully

Explanation: Leakage flux bypasses the intended armature path and reduces useful flux.

Question 154. The ratio of total flux produced by poles to useful flux in armature is called:

  1. A. Leakage coefficient
  2. B. Power factor
  3. C. Slip
  4. D. Voltage regulation

Answer: A. Leakage coefficient

Explanation: Leakage coefficient accounts for flux that does not usefully link armature conductors.

Question 155. The function of the yoke in a DC generator is:

  1. A. Mechanical support and magnetic return path
  2. B. Only current rectification
  3. C. Only speed control
  4. D. Only brush insulation

Answer: A. Mechanical support and magnetic return path

Explanation: The yoke holds poles and provides a low-reluctance return path for flux.

Question 156. The pole core is usually made of cast steel or laminated steel to:

  1. A. Carry magnetic flux and support field coil
  2. B. Act as a brush
  3. C. Rectify current
  4. D. Increase air gap

Answer: A. Carry magnetic flux and support field coil

Explanation: Pole cores carry flux and hold the field windings.

Question 157. The main advantage of laminated pole shoes in some DC machines is:

  1. A. Reduction of eddy current loss due to armature slotting effects
  2. B. Increase of copper loss
  3. C. Removal of commutator
  4. D. Increase of friction

Answer: A. Reduction of eddy current loss due to armature slotting effects

Explanation: Pulsations caused by slotting can induce eddy currents in pole shoes.

Question 158. The air gap in a DC machine should be:

  1. A. Small and uniform as far as practical
  2. B. Very large always
  3. C. Zero always
  4. D. Only on one side

Answer: A. Small and uniform as far as practical

Explanation: A small uniform air gap reduces magnetizing requirement and improves performance.

Question 159. Too small an air gap may cause:

  1. A. Mechanical rubbing and sensitivity to armature reaction
  2. B. No magnetic flux
  3. C. No current
  4. D. Zero noise always

Answer: A. Mechanical rubbing and sensitivity to armature reaction

Explanation: Very small gaps can create mechanical clearance problems and distortion effects.

Question 160. A generator has 4 poles, 720 conductors, flux 0.015 Wb, speed 1000 rpm and lap winding. EMF is:

  1. A. 180 V
  2. B. 270 V
  3. C. 360 V
  4. D. 720 V

Answer: A. 180 V

Explanation: For lap, A=P=4, so E = 4×0.015×720×1000/(60×4)=180 V.

Question 161. A wave-wound generator has 4 poles, 720 conductors, flux 0.015 Wb and speed 1000 rpm. EMF is:

  1. A. 180 V
  2. B. 360 V
  3. C. 540 V
  4. D. 720 V

Answer: B. 360 V

Explanation: For wave winding A=2, so E = 4×0.015×720×1000/(60×2)=360 V.

Question 162. A lap-wound generator has 8 poles. Number of parallel paths for simplex lap winding is:

  1. A. 2
  2. B. 4
  3. C. 8
  4. D. 16

Answer: C. 8

Explanation: In simplex lap winding, the number of parallel paths equals the number of poles.

Question 163. A duplex lap-wound 4-pole generator has parallel paths equal to:

  1. A. 4
  2. B. 6
  3. C. 8
  4. D. 2

Answer: C. 8

Explanation: For duplex lap winding, A = 2P = 8.

Question 164. A duplex wave-wound DC generator has parallel paths equal to:

  1. A. 2
  2. B. 4
  3. C. P
  4. D. 2P

Answer: B. 4

Explanation: For duplex wave winding, A = 2 × 2 = 4 parallel paths.

Question 165. If the field current of a separately excited generator is increased while speed is constant, generated voltage generally:

  1. A. Increases until saturation
  2. B. Decreases to zero
  3. C. Remains exactly constant
  4. D. Becomes AC

Answer: A. Increases until saturation

Explanation: Increasing field current increases flux and EMF, but saturation limits the increase.

Question 166. The load characteristic of a DC shunt generator is more drooping than that of a separately excited generator because:

  1. A. Field current decreases with terminal voltage
  2. B. It has no brushes
  3. C. It has no armature reaction
  4. D. Its speed is always zero

Answer: A. Field current decreases with terminal voltage

Explanation: As terminal voltage falls, shunt field current also falls, further reducing generated EMF.

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Quick Answer Key for DC Generator MCQs

The table below helps you revise all answers quickly before exams.

Q. No. Level Answer Correct Option
1EasyCSilicon steel
2EasyBEddy current loss
3EasyBCopper
4EasyCMica
5EasyBMechanical energy into DC electrical energy
6EasyBFaraday's law of electromagnetic induction
7EasyBInduced EMF in a generator
8EasyBDirection of magnetic field
9EasyCMotion of conductor
10EasyBInduced current or EMF
11EasyBConvert internally induced AC into DC at terminals
12EasyBCommutator
13EasyACarbon
14EasyBYoke
15EasyBArmature
16EasyBMain magnetic flux
17EasyBSpread magnetic flux uniformly
18EasyBRotor shaft
19EasyAMechanical input power
20EasyACopper
21EasyAFlux density, length and velocity
22EasyCAlternate north and south poles
23EasyBArmature coils
24EasyBPrevent short circuit between conductors and core
25EasyBCommutator and brushes
26EasyBGenerated EMF in the short-circuited coil is ideally zero
27EasyBZero or very small
28EasyBIn parallel with armature terminals
29EasyBIn series with armature and load
30EasyBAn external DC source
31EasyAInitial voltage build-up
32EasyBFail to build up voltage
33EasyBRestoring residual magnetism using a DC source
34EasyBSevere sparking or rough commutator
35EasyBRemove heat
36EasyAHysteresis and eddy current losses
37EasyAFriction and windage
38EasyAIa²Ra
39EasyAArmature resistance drop
40EasyAFlux and speed
41IntermediateAE = PΦZN / 60A
42IntermediateBNumber of parallel paths
43IntermediateBNumber of poles
44IntermediateA2
45IntermediateBLow voltage, high current
46IntermediateBHigh voltage, low current
47IntermediateBLap-wound armatures
48IntermediateBEqual to the number of poles
49IntermediateBLow voltage and high current
50IntermediateBDifference of back and front pitch
51IntermediateAReduce copper in end connections and improve commutation
52IntermediateBArmature current magnetic field on main field
53IntermediateACross-magnetizing
54IntermediateBReduction in generated EMF
55IntermediateANeutralize armature reaction under pole faces
56IntermediateBArmature winding
57IntermediateAImprove commutation
58IntermediateBMagnetic neutral axis
59IntermediateBSparking and demagnetization
60IntermediateBNeutral axis
61IntermediateAChanging AC armature output into DC at terminals
62IntermediateBReduce ripple in generated DC
63IntermediateBBrush jumping and sparking
64IntermediateAAllow brushes to contact copper segments properly
65IntermediateASame as the main pole ahead in direction of rotation
66IntermediateBSparking and scarring at related commutator segment
67IntermediateDAll of the above
68IntermediateDAll of the above
69IntermediateDAll of the above
70IntermediateAMaximum field circuit resistance for voltage build-up at a given speed
71IntermediateABelow which generator fails to build up for given field resistance
72IntermediateBIncreases critical resistance
73IntermediateBDecreases and may fail to build up
74IntermediateAMagnetization characteristic
75IntermediateATerminal voltage and load current
76IntermediateAGenerated EMF and armature current
77IntermediateDAll of the above
78IntermediateANo load current means no series field current
79IntermediateAFeeder booster
80IntermediateABattery charging and general DC supply
81IntermediateCGreater than no-load voltage
82IntermediateAAlmost equal to no-load voltage
83IntermediateBOpposing shunt field flux
84IntermediateASlightly higher than battery voltage
85IntermediateAField current
86IntermediateBDoubles
87IntermediateC240 V
88IntermediateC580 V
89IntermediateB4 V
90IntermediateB4
91IntermediateA2
92IntermediateAIt has fewer parallel paths
93IntermediateAIt has more parallel paths
94IntermediateAIron loss and mechanical loss
95IntermediateASpeed and flux density
96IntermediateASpeed
97IntermediateAVariable copper loss equals constant loss
98IntermediateAAs low as possible
99IntermediateARotating energy converter
100IntermediateAUseful EMF is induced
101IntermediateAInter-polar region
102IntermediateABetter commutation and less commutator wear
103IntermediateALow voltage and high current are involved
104IntermediateALower contact voltage drop
105IntermediateARapid brush wear
106IntermediateAApproximately flat-topped under pole arc
107IntermediateDAll of the above
108HardB320 V
109HardA270 V
110HardB600
111HardC255 V
112HardB0.2 Ω
113HardB2 A
114HardC102 A
115HardC80 A
116HardC82 A
117HardC500 W
118HardA90.9%
119HardC80 A
120HardC260 V
121HardC232 V
122HardADrooping voltage characteristics
123HardASame polarity and nearly same voltage as busbar
124HardAAvoid sudden current and mechanical shock
125HardAImprove load sharing and prevent reversal of series field effect
126HardAIts generated EMF becomes lower than busbar voltage
127HardAIn the direction of rotation
128HardAForward in direction of rotation
129HardADemagnetization at leading tip and magnetization at trailing tip
130HardAProvide mechanical balance
131HardBFail to build or build in wrong direction
132HardACheck/reverse field connections if needed
133HardAMagnetic saturation
134HardAResidual magnetism
135HardAZero
136HardAField winding has inductance
137HardALoad current flows
138HardACompensates feeder voltage drop
139HardAFlux increases with load current
140HardAArmature and series field resistance drops
141HardAIa - Ish
142HardAIa = Ise = IL
143HardADegree of compounding
144HardALevel-compounded generator
145HardAVoltage falls sharply with load
146HardAField current is independent of load current
147HardAApproximately constant over normal current range
148HardASparking at brushes
149HardASelf-inductance of the short-circuited coil
150HardAReactance voltage and local armature reaction in commutating zone
151HardAPole shoes
152HardAIn series with armature
153HardADoes not link with armature conductors usefully
154HardALeakage coefficient
155HardAMechanical support and magnetic return path
156HardACarry magnetic flux and support field coil
157HardAReduction of eddy current loss due to armature slotting effects
158HardASmall and uniform as far as practical
159HardAMechanical rubbing and sensitivity to armature reaction
160HardA180 V
161HardB360 V
162HardC8
163HardC8
164HardB4
165HardAIncreases until saturation
166HardAField current decreases with terminal voltage

Exam Preparation Tips for DC Generator

  • Revise the EMF equation: E = PΦZN / 60A.
  • Remember the difference between lap winding and wave winding.
  • Understand armature reaction instead of memorizing only definitions.
  • Practice numerical questions on generated EMF, terminal voltage and efficiency.
  • For interviews, prepare the function of commutator, brushes, interpoles and compensating winding.

Frequently Asked Questions on DC Generator MCQs

1. What is a DC generator?

A DC generator is a machine that converts mechanical energy into direct current electrical energy using electromagnetic induction.

2. Which law is used in DC generator operation?

A DC generator works on Faraday’s law of electromagnetic induction.

3. Why is the armature core laminated?

The armature core is laminated to reduce eddy current loss and heating.

4. What is the function of a commutator in a DC generator?

The commutator converts the alternating EMF induced in the armature into unidirectional DC at the output terminals.

5. Which winding is used for high current DC generators?

Lap winding is preferred for low voltage and high current DC generators.

6. Which winding is used for high voltage DC generators?

Wave winding is preferred for high voltage and low current DC generators.

7. What is armature reaction?

Armature reaction is the effect of armature current flux on the main field flux of the DC generator.

8. What is the use of interpoles?

Interpoles improve commutation and reduce sparking at the brushes.

Suggested Blogger Labels

DC Generator MCQ, Electrical Machines MCQ, Electrical Engineering MCQ, SSC JE Electrical, RRB JE Electrical, GATE Electrical, ITI Electrician, Diploma Electrical

Internal Linking Suggestions

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Conclusion

These DC Generator MCQ questions and answers cover the most important concepts of DC machines in a simple and exam-oriented way. If you are preparing for electrical engineering exams, diploma exams, ITI exams, SSC JE, RRB JE, GATE basics or technical interviews, revise these questions regularly and focus on the explanations.

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Note: These MCQs are written in original simple wording for learning and exam practice. Concepts are based on standard Electrical Machines topics such as DC generator construction, EMF equation, commutation, armature reaction and generator characteristics.

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