DC Machines MCQs | DC Machines MCQs and Answers for competitive exams

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Questions
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%

Answer: Increase by 4%
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

Answer: Shunt motor
83 DC motors are considered most suitable for the applications in
A Fans
B Water pumps
C Traction
D flour mills

Answer: Traction
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

Answer: Increases
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

Answer: Field winding
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

Answer: Increases
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

Answer: Increase
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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