SSC JE Electrical MCQ

81. The average value of the voltage wave v = 110 + 175 sin (314t – 25°) volts is

(a) 110 V
(b) 175 V
(c) 165.57 V
(d) 206.7 V

82. A current from an AC source divides into two branches A and B in parallel. Branch A is an inductor …….µH inductance and 1W resistance. Branch B is another inductor with inductance L and 1.5 Ω resistance. For the ratio of currents in the branches to be independent of supply frequency, value of L should be

(a) 30.5 µH
(b) 20 µH
(c) 45 µH
(d) 29.5 µH

Answer: (c) 45 µH

83. A universal motor is one which

(a) can run on any value of supply voltage
(b) has infinitly varying speed
(c) can operate on ac as well as dc voltage
(d) can work as single phase or three phase

84. If the centrifugal switch of a single phase resistance split induction motor does not open after starting of motor, the motor

(a) will run above normal speed
(b) will run below normal speed
(c) will draw very small current
(d) will draw high current and get over heated

85. Alternators are usually designated to generate which type of AC voltage ?

(a) with fixed frequency
(b) with variable frequency
(c) fixed current
(d) fixed power factor

86. Three inductors each of 60 mH are connected in delta. The value of inductance of each arm of the equivalent star connection is

(a) 10 mH
(b) 15 mH
(c) 20 mH
(d) 30 mH

87. The magnetic field energy in an inductor changes from maximum value to minimum value in 5 msec when connected to an AC source. The frequency of the source in Hz is

(a) 500
(b) 200
(c) 50
(d) 20

88. A voltage source having an open-circuit voltage of 150 V and internal resistance of 75 Ω  is equivalent to a current source of

(a) 2A in series with 75Ω
(b) 2A in parallel with 37.5Ω
(c) 2A in parallel with 75Ω
(d) 1 A in parallel with 150Ω

89. A 300 kW alternator is driven by a prime mover of speed regulation 4% while the prime mover of another 200 kW alternator has a speed regulation of 3%. When operating in parallel; the total load they can take without any of them being overloaded is

(a) 500 kW
(b) 567 kW
(c) 425 kW
(d) 257 kW

90. The commutator in DC machine acts as

(a) a mechanical inverter
(b) a mechanical rectifier
(c) current controller
(d) either (a) or (b)

91. The purpose of using dummy coil in DC machine is to

(a) eliminate harmonics developed in the machine
(b) eliminate harmonics reaction
(c) bring mechanical balance of the armature
(d) bring mechanical balance of the body of the motor

92. An inductor with a ferromagnetic core is supplied from a sinusoidal voltage source with frequency ‘f ‘. The current drawn by the inductor will be

(a) sinusoidal with frequency ‘f ‘
(b) sinusoidal with frequency ‘2f ‘
(c) a sawtooth wave
(d) non-sinusoidal with frequency ‘f ‘

93. For a 6-pole DC machine with wave wound armature, the number of brushes required is

(a) 2
(b) 4
(c) 6
(d) 12

94. Function of interpoles in a DC machine is to

(a) reduce field winding heating
(b) improve commutation
(c) compensate for air gap variation
(d) reduce losses

95. The commutator segments of DC machine are made of

(a) tungsten
(b) hard drawn copper
(c) soft copper
(d) electrolytic copper

96. Which one of the following is a speed control method of three phase squirrel cage induction motor?

(a) Plugging method
(b) Star – delta switch method
(c) Pole changing method
(d) Centrifugal clutch method

97. In the circuit as shown, voltage measured between A, B, is found to be 70 V. Value of M is

(a) 30 mH
(b) 100 mH
(c) 200 mH
(d) 70 mH

98. Two coupled coills, connected in a series have and equivalent inductance of 16 mH or 8 mH depending on the connection. The mutual inductance between the coil is

(a) 12 mH
(b) 8 2 mH
(c) 4 mH
(d) 2 mH

Answer: (d) 2 mH

99. Tesla is the unit of

(a) electric flux density
(b) magnetic field intensity
(c) electric field intensity
(d) magnetic flux density

100. Which one of the following is a valid value of coefficien of coupling between two inductors?

(a) 1.414
(b) 0.2
(c) 1.732
(d) 17.32