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Free download in PDF DC Machines Short Questions and Answers for competitive exams. These short objective type questions with answers are very important for competitive exams like IIT-JEE, NEET, AIIMS, JIPMER etc. These short solved questions or quizzes are provided by Gkseries.
41
Carbon brushes are used in electric motors to
[A]
Prevent sparking during commutation
[B]
Provide a path for flow of current
[C]
Brush off carbon deposits on the commutator
[D]
None 0f these
Answer: Provide a path for flow of current
42
Interpoles in dc motors are used for
[A]
Increasing the speed of motor
[B]
Reducing sparking at the commutation
[C]
Decreasing the counter emf
[D]
Converting armature current to dc
Answer: Reducing sparking at the commutation
43
Small dc motors upto 5 HP usually have
[A]
2 poles
[B]
4 poles
[C]
6 poles
[D]
8 poles
44
The resistance of the starter of a 220 v, 5 HP dc shunt motor is of the order of
[A]
0.01Ω
[B]
0.1Ω
[C]
1Ω
[D]
10Ω
45
A dc motor can be easily identified by
[A]
Yoke
[B]
Size of conductor
[C]
Commutator
[D]
Winding
46
The back emf of a dc motor
[A]
Adds to the supply voltage
[B]
Regulates its armature voltage
[C]
Helps in energy conversion
[D]
Usually exceeds the supply voltage
Answer: Helps in energy conversion
47
In a dc motor, pole shoes are fixed to the magnet core by
[A]
Set of screws
[B]
Key
[C]
Soldering
[D]
Welding
48
In a dc motor, the ratio of back emf to supply emf is an indication of its
[A]
Efficiency
[B]
Speed regulation
[C]
Starting torque
[D]
Running torque
49
The value of diverter resistance for a series dc motor is of the order of
[A]
0.1Ω
[B]
2Ω
[C]
20Ω
[D]
400Ω
50
A large series motor is never started without some load on it, otherwise
[A]
It draws very current
[B]
It develops excessive speed and get damaged
[C]
There results heavy sparking at the brushes
[D]
Circuit gets open circuited
Answer: It develops excessive speed and get damaged
51
When load is removed, which of the following dc motors will run at excessively high speed?
[A]
Shunt motor
[B]
Series motor
[C]
Cumulative compound motor
[D]
Differential compound motor
52
Speed of a motor may be varied by varying
[A]
Field current
[B]
Applied voltage
[C]
Resistance in series with armature
[D]
Any of these
53
The speed of a dc motor is
[A]
Always constant
[B]
Directly proportional to back emf
[C]
Directly proportional to flux
[D]
Inversely proportional to the product of back emf and flux
Answer: Directly proportional to back emf
54
The highest speed attained by a dc shunt motor at rated flux is
[A]
Infinity
[B]
Higher than no load speed
[C]
Equal to the no load speed
[D]
Lower than the no load speed
Answer: Equal to the no load speed
55
A dc motor is preferred to an ac motor for the application in
[A]
Low speed operation
[B]
High speed operation
[C]
Variable speed variation
[D]
Fixed speed operation
Answer: Variable speed variation
56
If 220 V dc series motor is connected to a 220 V ac supply, then at will
[A]
Not run
[B]
Burn out
[C]
Run smoothly
[D]
Run with less efficiency and high sparking
Answer: Run with less efficiency and high sparking
57
Which of the following dc motor has approximately constant speed?
[A]
Series motor
[B]
Shunt motor
[C]
Cumulatively compound motor
[D]
Differentially compound motor
58
The back emf of dc motor depends on
[A]
Armature speed N
[B]
Field flux ɸ
[C]
Number of armature conductors
[D]
All of these
59
When the direction of power flow reverses, a differentially compounded motor becomes
[A]
Differentially compounded generator
[B]
A shunt generator
[C]
Cumulatively compounded generator
[D]
A series generator
Answer: Cumulatively compounded generator
60
When the direction of power flow reverses, a cumulatively compounded motor becomes
[A]
A differentially compounded generator
[B]
A cumulative compounded generator
[C]
A shunt generator
[D]
A series generator
Answer: A differentially compounded generator
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