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Free download in PDF DC Machines MCQs 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.
81
If the load current and flux of dc motor are kept construe while the voltage applied across the armature is increased by 4 percent, the aped of the motor will
[A]
Remain unchanged
[B]
Decrease by 4%
[C]
Increase by 4%
[D]
Increase by 16%
82
Which dc motor will have highest percentage increase in input current for a given percentage increase in torque?
[A]
Series motor
[B]
Shunt motor
[C]
Cumulatively compound motor
[D]
Separately excited motor
83
DC motors are considered most suitable for the applications in
[A]
Fans
[B]
Water pumps
[C]
Traction
[D]
flour mills
84
If the speed of a dc shunt motor increases, the back emf
[A]
Increases
[B]
Decreases
[C]
Remains unchanged
[D]
Fist increases and then decreases
85
If the pole flux of a dc motor approaches zero, its speed will
[A]
Approach zero
[B]
Approach infinity
[C]
Not change
[D]
Approach a stable value between zero and infinity
Answer: Approach infinity
86
If the load on a dc shunt motor is increased, its speed decreases primarily due to
[A]
Increase in its flux
[B]
Decrease in back emf
[C]
Increase in armature current
[D]
Decrease in brush drop
Answer: Decrease in back emf
87
The shaft torque of a dc motor is less than its armature torque because of
[A]
Copper losses
[B]
Mechanical losses
[C]
Back emf
[D]
Rotational losses
Answer: Rotational losses
88
The armature torque of a dc motor is a function of its
[A]
Field flux alone
[B]
Armature current along
[C]
Speed alone
[D]
Both field flux and armature current
Answer: Both field flux and armature current
89
Two dc series motor are mechanically coupled. One machine runs as motor and the other as generator. The iron losses of the two machines will be identical when
[A]
Both have the same excitation
[B]
Both have the same speed
[C]
Both have the same back emf
[D]
Both operate at the same voltage
Answer: Both have the same excitation
90
Two dc series motor are coupled. One motor runs as generator and the other as motor. The friction losses of the two machines will be equal when
[A]
Both operate at same voltage
[B]
Both have same back emf
[C]
Both have same speed
[D]
Both have same excitation
Answer: Both have same speed
91
In dc motor, which of the following part can withstand the maximum rise in temperature?
[A]
Armature winding
[B]
Field winding
[C]
Commutator winding
[D]
Slip rings
92
If the back emf of a dc motor suddenly vanishes
[A]
The motor will run faster
[B]
The motor will start hunting the efficiency of the motor will increase
[C]
The motor will start hunting
[D]
The motor will burn out
Answer: The motor will burn out
93
Torque of a motor is
[A]
Force on N-m acting on the rotor
[B]
Product of tangential force on the rotor and its radius
[C]
The electrical power in kW
[D]
Power given to the load
Answer: Product of tangential force on the rotor and its radius
94
Which of the following statements about a series motor is correct
[A]
It can run easily without load.
[B]
It has poor torque
[C]
It has an almost constant speed
[D]
Its field winding consists of small number of thick wires
Answer: Its field winding consists of small number of thick wires
95
The speed of a series dc motor at no load is
[A]
Zero
[B]
Medium
[C]
High
[D]
Tending to infinity
Answer: Tending to infinity
96
The speed of a dc series motor decreases if the flux in the field winding
[A]
Remains constant
[B]
Decreases
[C]
Increases
[D]
None of these
97
The direction of rotation of a dc series motor can be reversed by interchanging
[A]
The supply terminals only
[B]
The field terminals only
[C]
The supply and the field terminals
[D]
None of these
Answer: The field terminals only
98
If the field circuit of a dc shunt motor running at rated speed gets open circuited, then immediately thereafter the speed of the motor would tent to
[A]
Decrease
[B]
Increase
[C]
Remain unchanged
[D]
Increase excessively
99
The mechanical power developed by the armature of a dc motor is equal to
[A]
power input mainus copper loss
[B]
armature current multiplied by back emf
[C]
armature current multiplied by supply emf
[D]
power input minus mechanical loss
Answer: armature current multiplied by back emf
100
The dc compound motors are generally
[A]
Cumulative compound
[B]
Differential compound
[C]
Level compound
[D]
None of these
Answer: Cumulative compound
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