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
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
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
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
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
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