Electrical Machines(DC Machines) :

76. If a shunt motor is started with its field winding open then

a. It will rotate at the same speed as that with its field winding closed
b. It will rotate at less speed as that with its field winding closed
c. It will rotate at dangerously high speed
d. None of these

77. D.C. shunt motors are commonly used in

a. Cranes
b. Electric traction
c. Elevators
d. Lathe machines

78. For d.c. series motor, if I_a is the armature current then the torque developed is

a. α I_a
b. α I_a²
c. α (1 / I_a²)
d. α (1 / I_a)

79. Neglecting saturation, if the current drawn from by a d.c. series motor is increased from 15 A to 18 A, then the increase in the torque expressed as percentage of initial torque will be

a. 22 %
b. 33%
c. 44%
d. 56.78%

80. A 4 pole 240 V, d.c. series motor has a wave wound armature with 180 conductors. The armature resistance and the field winding resistance are 0.10 ohm and 0.2 ohm respectively. If the motor is drawing 40 A current at 0.015 Wb flux per pole, then the speed under this condition is

a. 2533.3 rpm
b. 2644.4 rpm
c. 2756.9 rpm
d. 2987.6 rpm

81. 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

82. 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

83. 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

84. 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

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

a. Yes
b. No

86. 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

87. 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

88. 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 light load or no load?

a. Yes
b. No

89. 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

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

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

91. In electric traction, which type of motor is generally used?

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

92. Differential compound motors are mainly used in

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

93. 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

94. 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

95. 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

96. 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

97. f 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

98. 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

99. 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

100. 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