ELECTRICIAN SEM-3

 ELECTRICIAN SEM-3 MCQ

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1 What is the name of the part marked as ‘X’ in DC generator?

A  Armature core

B Brush 

C Commutator raiser 

D Commutator segment

Correct Answer:- C Commutator raiser

2 What is the name of D.C generator? 

A  Differential long shunt compound

B Differential short shunt compound

C Cumulative long shunt compound

D Cumulative short shunt compound

Correct Answer:- A Differential long shunt compound

3 Which rule is used to find the direction of induced emf in D.C generator?

A Cork screw rule 

B Right hand palm rule

C Fleming’s left hand rule

D Fleming’s right hand rule

Correct Answer:- D Fleming’s right hand rule

4 Which formula is used to calculate the generated emf in D.C generator?

A Generated emf = 

B Generated emf = 

C Generated emf = 

D Generated emf = 

Correct Answer:- C Generated emf = 

5 What is the formula to calculate back emf of a D.C motor?

A 

B 

C 

D 

Correct Answer:- C

6 What is the name of the part marked ‘X’ in DC generator?

A Pole tip 

B Pole coil 

C Pole core 

D Pole shoe

Correct Answer:- D Pole shoe

7 What is the name of the D.C generator? 

A Shunt generator 

B Series generator 

C Compound generator

D Separately excited generator

Correct Answer:- D Separately excited generator

8 Which energy is converted into electrical energy by generator?

A Heat 

B Kinetic 

C Chemical 

D Mechanical

Correct Answer:- D Mechanical

9 What is the name of D.C generator's field? 

A Short shunt compound generator

B Long shunt compound generator

C Differential compound generator

D Cumulative compound generator

Correct Answer:- D Cumulative compound generator

10 What is the principle of D.C generator? 

A Cork screw rule 

B Fleming’s left hand rule

C Fleming’s right hand rule

D Faradays laws of electromagnetic induction

Correct Answer:- D Faradays laws of electromagnetic induction

11 What is the formula for dynamically induced emf? 

A BLV volts 

B BL sinθ volts 

C BLV sinθ volts 

D BLV cosθ volts

Correct Answer:- C BLV sinθ volts 

12 Which rule is used to find direction of magnetic field?

A Cork screw rule 

B Right hand palm rule

C Fleming’s left hand rule

D Fleming’s right hand rule

Correct Answer:- D Fleming’s right hand rule

13 What is the name of the part of DC generator? 

A Stator 

B Pole core 

C Pole shoes 

D Yoke (or) frame

Correct Answer:- D Yoke (or) frame

14 How many parallel paths in duplex lap winding of a 4 pole DC generator?

A 4

B 6

C 8

D 12

Correct Answer:- C 8

15 Name the part of DC generator? 

A Side end plates

B Pole shoe lamination

C Commutator segment

D Armature core lamination

Correct Answer:- D Armature core lamination

16 How interpoles are connected in a DC generator? 

A In series with armature

B In parallel with armature

C In series with shunt field

D In parallel with shunt field

Correct Answer:- A In series with armature

17 What is the necessity of residual magnetism in a self excited DC generator?

A Build up the voltage

B Reduce the field current

C Reduce armature current

D Maintain constant output voltage

Correct Answer:- A Build up the voltage

18 Which are the two points that the brush contact resistance measured in D.C machines?

A Resistance between the opposite brushes

B Resistance between brush and commutator raiser

C Resistance between brush and commutator

D Resistance between brush and armature conductors

Correct Answer:- C Resistance between brush and commutator

19 Which voltage drop is indicated in the portion marked as ‘X’?

A Full load voltage drop

B Armature voltage drop

C Armature reaction drop

D Shunt field voltage drop

Correct Answer:- C Armature reaction drop

20 What is the name of the compound generator, if the shunt field is connected in parallel with armature?

A Long shunt compound

B Cumulative compound

C Differential compound

D Short shunt compound

Correct Answer:- D Short shunt compound

21 Why the armature core of a DC generator is laminated?

A Reduce the copper loss

B Reduce the friction loss

C Reduce the hysteresis loss

D Reduce the eddy current loss

Correct Answer:- D Reduce the eddy current loss

22 Why armature resistance of a D.C generator is very low?

A Reduce armature current

B Reduce armature voltage drop

C Run armature with less weight

D Reduce the temperature of armature

Correct Answer:- B Reduce armature voltage drop

23 Why the D.C generator should run in clockwise direction only?

A Protect brushes from damage

B Protect the residual magnetism

C Avoid short circuit in armature

D Avoid over loading of generator

Correct Answer:- B Protect the residual magnetism

24 Why compensating winding is provided in large DC generators?

A Connect more loads

B Reduce commutation effect

C Neutralize armature reaction effect

D Increase the efficiency of generator

Correct Answer:- C Neutralize armature reaction effect

25 What is the reason for DC generator fails to build up voltage?

A Loose brush contact

B Armature resistance is more

C Field resistance is above critical resistance

D Prime mover is running at above rated speed

Correct Answer:- C Field resistance is above critical resistance

26 What is the name of generator, if its field is connected in parallel with armature?

A Shunt generator 

B Series generator 

C Compound generator

D Self excited generator

Correct Answer:- A Shunt generator 

27 What is the purpose of pole shoe in DC generator? 

A Reduce the air gap

B Increase the field strength

C Minimize the magnetic losses

D Spread out flux uniformly in the air gap

Correct Answer:- D Spread out flux uniformly in the air gap

28 What is the function of split rings in DC generator? 

A Maintain constant voltage

B Collects the current unidirectionally

C Reduces the voltage drop at brushes

D Increases the terminal voltage than rated

Correct Answer:- B Collects the current unidirectionally

29 Which material is used to make brush in generator? 

A Steel and graphite 

B Carbon and graphite

C Cast iron and graphite

D Aluminium and graphite

Correct Answer:- B Carbon and graphite

30 Why DC generators are loosing their residual magnetism?

A Heavy short circuit in load

B Running without load continuously

C Continuous running without break

D Change of direction of rotation very often

Correct Answer:- D Change of direction of rotation very often

31 How does the magnetic circuit complete through the yoke and poles in a generator?

A Field coils 

B Armature core 

C Laminated pole core

D Winding conductors in armature

Correct Answer:- B Armature core 

32 Why the terminal voltage decreases if load increases in DC shunt generator?

A Because of armature reaction effect

B Due to increased in armature resistance

C Because of brush voltage drop decreases

D Due to increased in shunt field inductance

Correct Answer:- A Because of armature reaction effect

33 Which type of DC generator is used for long distance distribution lines?

A Shunt generator 

B Series generator 

C Differential compound generator

D Cumulative compound generator

Correct Answer:- D Cumulative compound generator

34 Which method is used to improve the insulation resistance in DC generator?

A Replacing the brushes frequently

B Heating the machine by running periodically

C Cleaning the commutator segments regularly

D Blowing hot air into the machine during maintenance

Correct Answer:- D Blowing hot air into the machine during maintenance

35 Which type of D.C Generator works in absence of residual magnetism?

A Shunt generator 

B Series generator 

C Compound generator

D Separately excited generator

Correct Answer:- D Separately excited generator

36 Which type of D.C generator is used for arc welding?

A Shunt generator 

B Series generator 

C Differential compound generator

D Cumulative compound generator

Correct Answer:- C Differential compound generator

37 What is the property of wave winding in D.C generator?

A Low current low voltage

B High current low voltage

C Low current high voltage

D High current high voltage

Correct Answer:- C Low current high voltage

38 What is the purpose of resistance wire used in the commutator connection in D.C generator?

A Maintain constant voltage

B Nullifying statically induced emf

C Increasing statically induced emf

D Smooth reversal of current direction

Correct Answer:- D Smooth reversal of current direction

39 Why solid pole shoes are used in D.C generator? 

A To reduce the copper loss

B To increase the residual magnetism

C To decrease the residual magnetism

D To reduce the reluctance of magnetic path

Correct Answer:- D To reduce the reluctance of magnetic path

40 Which metal is used to make large capacity DC generator yoke?

A Cast iron 

B Soft iron 

C Aluminium 

D Rolled Steel

Correct Answer:- D Rolled Steel

41 What is the function of split rings in a D.C generator?

A Supplies output continuously

B Makes output in the uni direction

C Makes output in the opposite direction 

D Collects the output from alternate conductors

Correct Answer:- B Makes output in the uni direction

42 Which type of voltage is induced dynamically in a D.C generator?

A Pulsating voltage 

B Oscillating voltage 

C Alternating voltage 

D Direct current voltage

Correct Answer:- C Alternating voltage 

43 What is the purpose of slot marked as ‘X’? 

A To fix the key way 

B To make air circulation

C For lubrication purpose

D For easy removal from shaft

Correct Answer:- A To fix the key way 

44 What is the purpose of field coils in D.C generator? 

A To increase the flux in air gap

B To decrease the magnetizing current

C To magnetize the poles to produce coil flux

D To increase the reluctance of magnetic path

Correct Answer:- C To magnetize the poles to produce coil flux

45 Which metal is used to make pole core of large DC generator machines?

A Soft iron 

B Cast iron 

C Cast steel 

D Stainless steel

Correct Answer:- C Cast steel 

46 Why the pole core stampings are laminated in DC generator?

A Reduce the friction loss

B Reduce the windage loss

C Reduce the hysteresis loss

D Reduce the eddy current loss

Correct Answer:- D Reduce the eddy current loss

47 Which type of DC generator is used for electroplating process?

A Shunt generator 

B Series generator 

C Differential compound generator

D Cumulative compound generator

Correct Answer:- A Shunt generator

48 What is the purpose of compensating winding in DC generator?

A Minimizes rough commutation

B Maintain constant output voltage

C Neutralizes the demagnetizing effect

D Decreases the excitation current of field coils

Correct Answer:- C Neutralizes the demagnetizing effect

49 What is the effect if the shunt field resistance is above critical resistance value in a D.C generator?

A Output voltage is pulsating

B Output voltage is above normal

C Generator fails to build up voltage

D Generator builds up voltage normally

Correct Answer:- C Generator fails to build up voltage

50 What is the effect of armature reaction in DC generator?

A Output voltage increases

B Output voltage decreases

C Output voltage is pulsating

D Output voltage will become zero

Correct Answer:- B Output voltage decreases

51 Calculate the emf generated in a 4 pole DC generator with simplex wave wound armature has

1020 conductors and driven at a speed of 1500 rpm, the flux / pole is 0.007 Weber's?

A 178 V 

B 243 V 

C 357 V 

D 428 V

Correct Answer:- C 357 V

52 How the effect of armature reaction can be neutralized in large DC generators?

A Using compensating winding

B Providing additional inter poles

C Increasing brush contact resistance

D Adding resistance wires with winding

Correct Answer:- A Using compensating winding

53 What is the effect in D.C generator, if it is kept ideal for long time?

A Field coil resistance increases

B Armature resistance increases

C Increase the armature reaction

D Looses its residual magnetism

Correct Answer:- D Looses its residual magnetism

54 Calculate the induced emf of 4 pole dynamo having 1000 rpm lap wound and total number of conductors is 600, the flux / pole is 0.064 wb?

A 160V 

B 320V 

C 480V 

D 640V

Correct Answer:- D 640V

55 What is the effect on induced emf if the main field flux get distorted in DC generator?

A Induced emf increases

B Induced emf decreases

C No change in induced emf

D Induced emf becomes zero

Correct Answer:- B Induced emf decreases

56 What is the cause for heavy sparking in brushes of DC generator?

A Short circuit in field winding

B Short circuit in armature winding

C MNA and GNA position changed

D Too much spring tension at brush

Correct Answer:- C MNA and GNA position changed

57 Which instrument is used to measure armature winding resistance?

A Megger 

B Multimeter 

C Series type  Ohm meter

D Kelvin bridge

Correct Answer:- D Kelvin bridge

58 Which instrument is used to test armature winding for short and open circuit?

A Tong Tester 

B Internal Growler 

C External Growler 

D Digital multimeter

Correct Answer:- C External Growler 

59 What is the name of the speed control method of DC motor?

A Field diverter method

B Field tapping method

C Voltage control method

D Armature diverter method

Correct Answer:- D Armature diverter method

60 Which winding wire is used for DC field coil? 

A Super enameled copper wire

B Single silk covered copper wire 

C Double silk covered copper wire

D PVC covered copper winding wire

Correct Answer:- A Super enameled copper wire

61 Which formula is used to calculate the speed of DC

motor?

A   

B 

C  

D 
Correct Answer:- A

62 How many parallel paths in duplex lap winding in the armature of 4 pole D.C Motor?

A 2        B 4       C 6       D 8

Correct Answer:- A 2 

63 Which rule determines the direction of rotation of armature in D.C motor?

A Right hand grip rule

B Right hand palm rule

C Fleming’s left hand rule

D Fleming’s right hand rule

Correct Answer:- C Fleming’s left hand rule

64 What is the name of D.C motor? 

A D.C shunt motor 

B D.C series motor 

C D.C differential compound motor

D D.C cumulative compound motor

Correct Answer:- A D.C shunt motor 

65 Which rule determines the direction of current in D.C motor?

A Right hand grip rule

B Right hand palm rule

C Fleming’s left hand rule

D Fleming’s right hand rule

Correct Answer:- D Fleming’s right hand rule

66 What is the formula to calculate the current taken by D.C shunt motor armature?

A  

B 

C  

D 

Correct Answer:- C 

66 Which rule is applied to identify the direction of flux in DC motor?

A Cork’s screw rule 

B Right hand grip rule

C Fleming’s left hand rule

D Fleming’s right hand rule

Correct Answer:- C Fleming’s left hand rule

67 Name the type of DC motor. 

A Shunt motor 

B Series motor 

C Long shunt compound motor

D Short shunt compound motor

Correct Answer:- D Short shunt compound motor

68 What is the formula to calculate back emf in a DC motor?

A  

B  

C  

D  
Correct Answer:- C  

69 What is the name of the equipment? 

A Megger 

B Earth resistance tester

C Internal growler 

D External growler

Correct Answer:- D External growler

70 What is the name of winding, if coil pitch is less than pole pitch?

A Full pitch winding 

B Half pitch winding 

C Long chorded winding

D Short chorded winding

Correct Answer:- D Short chorded winding

71 What is the purpose of series resistor connected with holding coil in a D.C four point starter?

A Limit the current in holding coil

B Increase the current in holding coil

C Increase the voltage in holding coil

D Decrease the voltage in holding coil

Correct Answer:- A Limit the current in holding coil

72 Which speed control method of D.C series motor is used for electric train?

A Field diverter method

B Field tapping method

C Armature diverter method

D Supply voltage control method

Correct Answer:- A Field diverter method

73 Why shunt field coil is connected in series with holding coil in D.C three point starter?

A Increase the holding coil current

B Decrease the holding coil current

C Protect the shunt field from over current

D Protect the motor in case of open in shunt field

Correct Answer:- D Protect the motor in case of open in shunt field

74 Why the direction of rotation is changed only by changing the armature current direction in a D.C compound motor?

A Maintain rated speed

B Maintain motor characteristics

C Avoid armature reaction effect

D Prevent motor from over loading

Correct Answer:- B Maintain motor characteristics

75 Which speed control methods offers below normal speed in DC shunt motor?

A Field control method

B Voltage control method

C Armature control method

D Ward Leonard system of speed control

Correct Answer:- C Armature control method

76 Why starters are required to start D.C motors in industries?

A Regulate the field voltage

B Reduce the armature current

C Control the armature reaction

D Smooth operation of motors

Correct Answer:- B Reduce the armature current

77 Which insulating material belongs to class ‘B’ insulation?

A Cotton 

B Bamboo 

C Fiber glass 

D Leatheroid paper

Correct Answer:- C Fiber glass 

78 What is the temperature value of class ‘F’ insulation?

A 90°C 

B 105°C 

C 120°C 

D 155°C

Correct Answer:- D 155°C

79 Which type of D.C motor is used for constant speed drives?

A DC series motor 

B DC shunt motor 

C Differential long shunt compound motor

D Differential short shunt compound motor

Correct Answer:- B DC shunt motor 

80 Which type of DC motor is used in elevators? 

A DC series motor 

B DC shunt motor 

C DC differential compound motor

D DC cumulative compound motor

Correct Answer:- D DC cumulative compound motor

81 Which method of speed control gives below the rated speed in DC series motor?

A Field diverter method

B Tapped field method

C Voltage control method

D Armature diverter method

Correct Answer:- D Armature diverter method

82 What is the effect, if a four point starter resistance is cutoff during running?

Motor stopped Runs at slow speed

Runs at very high speed

Runs at reverse direction

Correct Answer:- 

Correct Answer:- 

Correct Answer:-