# Electrical Machines Expected MCQ PDF 2 For Coal India Limited (CIL) MT Exam 2017

1)   The starting torque developed in the d.c. series motor and in d.c. shunt motor is

a. High, low
b. High, moderate
c. Moderate, low
d. Moderate, high

2)   The speed of a d.c. series motor is

a. Directly proportional to the both armature current and torque developed
b. Inversely proportional to the armature current and square root of torque developed
c. Directly proportional to the square of the armature current and square root of torque developed
d. Inversely proportional to the square of the armature current and square of torque developed

 ANSWER: Inversely proportional to the armature current and square root of torque developed

3)   The speed armature current characteristics of a d.c. series motor is

a. Rectangular hyperbola
b. Linear
c. Parabolic
d. Parabolic till saturation and then linear

4)   If a d.c. series motor is started on very light load or on no load then

a. It will run at dangerously high speed which may damage the motor mechanically
b. It will run at very low speed
c. Load does not effect the speed of d.c. series motor
d. None of these

 ANSWER: It will run at dangerously high speed which may damage the motor mechanically

5)   Can a d.c. series motor be used for applications in belt drives?

a. Yes
b. No

6)   D.C. series
motors are used in electric traction. What happens to the speed and
current of d.c motor if there is sudden slight drop in the mains
voltage?

a. Speed decreases and current also decreases
b. Speed decreases and current increases
c. Speed increases and current decreases
d. Speed decreases and current remains same

 ANSWER: Speed decreases and current remains same

7)   A long shunt compound motor and a short shunt compound motor can be

a. Cumulative type, differential type
b. Differential type, cumulative type
c. Both can be either cumulative or differential type
d. None of these

 ANSWER: Both can be either cumulative or differential type

8)   Cumulative
compound motor is capable of developing large amount of torque at low
speeds just like series motor. Can cumulative compound motor be run on

a. Yes
b. No

9)   The speed current characteristics are shown in the given figure. Identify the different curves.

a. 1 – series, 2 – shunt, 3 – cumulative compound, 4 – differential compound
b. 1 – cumulative compound, 2 – differential compound, 3 – series, 4 – shunt
c. 1 – cumulative compound, 2 – differential compound, 3 – shunt, 4 – series
d. 1 – differential compound, 2 – shunt, 3 – cumulative compound 4 – series

 ANSWER: 1 – differential compound, 2 – shunt, 3 – cumulative compound 4 – series

10)   In a differential compound d.c. motor, with increase in load, speed

a. Increases
b. Decreases
c. Remains same
d. None of these

11)   In electric traction, which type of motor is generally used?

a. Shunt motor
b. Series motor
c. Cumulative compound motor
d. Differential compound motor

12)   Differential compound motors are mainly used in

a. Drilling machines
b. Elevators
c. Electric traction
d. Not suitable for any practical application

 ANSWER: Not suitable for any practical application

13)   Which motor is not suitable for the application of centrifugal pumps?

a. Shunt motor
b. Series motor
c. Cumulative compound motor
d. Differential compound motor

14)   Due to
armature reaction magnetic neutral axis gets shifted by some angle. In
case of motors the brushes are shifted

a. Forwards same as the direction of rotation
b. Backwards opposite to the direction of rotation
c. Either (a) or (b)
d. Does not get shifted

 ANSWER: Backwards opposite to the direction of rotation

15)   Speed of d.c. shunt motors are controlled by

a. Flux control method
b. Rheostatic control method
c. Voltage control method
d. All of these

16)   With the increase in temperature, the speed of series and shunt motor will

a. Increase, decrease
b. Decrease, increase
c. Increase, increase
d. Decrease, decrease

17)   If a portion
of armature current is diverted through the diverter resistance, then
the speed of d.c. series motor

a. Remains same
b. Increases
c. Decreases
d. None of these

18)   A series wound motor is also called as universal motor because

a. It will run equally well using either an ac or a dc voltage source
b. It will run well below and above rated speed
c. It can be used in all kinds of applications
d. None of these

 ANSWER: It will run equally well using either an ac or a dc voltage source

19)   In the flux control method for controlling the speed of d.c. shunt motor, the speed control is not possible

a. Below normal rated speed
b. Above normal rated speed
c. Both (a) and (b)
d. None of these

20)   In armature
voltage control method or rheostatic control method for speed control in
d.c. shunt motor, a variable resistance is

a. Added in series with the armature
b. Added in series with the field
c. Connected across armature
d. Both in series with armature and field

21)   Which method is suitable for the speed control, below and above the normal rated speed of d.c. shunt motor?

a. Flux control method
b. Rheostatic control method
c. Voltage control method
d. All of these

22)   If a resistance is added in series with the field winding of d.c. shunt motor, then its

a. Both speed and torque decreases
b. Both speed and torque increases
c. Speed decreases, torque increases
d. Speed increases, torque decreases

23)   Ward-Leonard system is used for

a. Wide range of speed control
b. Very sensitive speed control
c. Both (a) & (b)
d. None of these

24)   For frequent starting, stopping and reversals, which motor is commonly used?

a. Permanent d.c. motor
b. Ward-Leonard system
c. Brushless d.c. motor
d. All of these

25)   The basic difference between three point starter and four point starter is

a. No volt coil is connected in
series with the field winding in three point starter while connected
independently across the supply in four point starter
b. No volt coil is connected across supply in three point starter while in series with field winding in four point starter.
c. No volt coil is connected across field winding in three point starter while connected across supply in four point starter.
d. None of these

 ANSWER: No volt coil is connected in series with the field winding in three point starter while connected independently across the supply in four point starter

26)   Which starter does not provide high speed protection to the d.c. shunt motor?

a. Three point starter
b. Four point starter
c. Two point starter
d. None of these

27)   For the protection of d.c. series motor, which starter is commonly used?

a. Two point starter
b. Three point starter
c. Four point starter
d. None of these

28)   The torque constant (Km),
of a permanent magnet d.c. motor is 0.25 V sec / radian and armature
resistance is 2 ohm. If the applied armature voltage is 90 V, then its
zero speed torque is

a. 10.45 N-m
b. 11.25 N-m
c. 13.65 N-m
d. 15.56 N-m

29)   The speed of permanent magnet d.c. motor cannot be controlled by

a. Flux control method
b. Rheostatic control method
c. Electronic circuits
d. None of these

30)   The number of windings on the field of permanent magnet d.c. motor is

a. More compared to shunt motor
b. Less compared to shunt motor
c. Absent
d. None of these

31)   Permanent magnet d.c. motors are extensively used in

a. Automobiles
b. Heaters
c. Air conditioners
d. All of these

32)   In the biomedical instruments like artificial heart pumps, the commonly used motor is

a. Permanent magnet d.c. motor
b. Brushless d.c. motor
c. Ward-Leonard system
d. Series motor

33)   A machine operating as motor may go into regenerative braking mode if its speed becomes

a. Sufficiently high to make back emf greater than supply voltage
b. Sufficiently low to make back emf greater than supply voltage
c. Sufficiently high to make back emf half of the supply voltage
d. Sufficiently low to make back emf half of the supply voltage

 ANSWER: Sufficiently high to make back emf greater than supply voltage

34)   In a three
phase induction motor, the resultant of three alternating fluxes,
separated from each other by 120 degree has constant amplitude

a. Equal to the maximum amplitude of an individual flux
b. Twice of the maximum amplitude of an individual flux
c. 1.5 times of the maximum amplitude of an individual flux
d. All of these

 ANSWER: 1.5 times of the maximum amplitude of an individual flux

35)   If the
frequency of a three phase induction motor is doubled and number of
poles is halved, then its synchronous speed is given by

a. Remains same
b. Becomes double of the original synchronous speed
c. Becomes four times of the original synchronous speed
d. Becomes half of the original synchronous speed

 ANSWER: Becomes four times of the original synchronous speed

36)   A three phase 4 pole, induction motor is supplied from 50 Hz supply. Then its synchronous speed will be

a. 1000 rpm
b. 1500 rpm
c. 1600 rpm
d. 2000 rpm

37)   In a three phase induction motor, the direction of rotation of rotating magnetic field can be reversed by

a. Interchanging any two terminals of three phase winding while connecting it to ac supply
b. by reversing the direction of rotating magnetic field
c. Cannot be changed
d. None of these

 ANSWER: Interchanging any two terminals of three phase winding while connecting it to ac supply

38)   For connecting the rotating member of machine to the external stationary circuit,

a. Slip rings and brush assembly is used
b. Only slip ring is used
c. Only brushes are used
d. Directly connected to the external stationary circuit

 ANSWER: Slip rings and brush assembly is used

39)   If the air gap of the induction motor increases then its power factor

a. Increase
b. Decreases
c. Remains same
d. Either increases or decreases

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