MCQOPTIONS
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MCQOPTIONS
This section includes 554 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics & Communication Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
A single-phase half-wave thyristor circuit with R load is triggered at anangle of α = 0°. As such, the maximum value of the average output voltage would be given by Consider Vs = Vm sinωt. |
| A. | Vm |
| B. | 2Vm/π |
| C. | Vm/π |
| D. | Vm/α |
| Answer» D. Vm/α | |
| 52. |
Calculate the output voltage of the Buck converter if the supply voltage is789 V and duty cycle value is .9. |
| A. | 711.1 V |
| B. | 710.1 V |
| C. | 722.2 V |
| D. | 713.2 V |
| Answer» C. 722.2 V | |
| 53. |
Ripple factor is the ratio of |
| A. | Rms value of the ac component of load voltage to the dc voltage |
| B. | Average value of the ac component of load voltage to the peak value of voltage |
| C. | Average value of the dc component of load voltage to the ac voltage |
| D. | Peak value of the dc component of load voltage to the ac voltage |
| Answer» C. Average value of the dc component of load voltage to the ac voltage | |
| 54. |
Silicon controlled rectifier can be turned on |
| A. | By applying a gate pulse and turned off only when current becomes zero |
| B. | And turned off by applying gate pulse |
| C. | By applying a gate pulse and turned off by removing the gate pulse |
| D. | By making current non zero and turned off by making current zero |
| Answer» B. And turned off by applying gate pulse | |
| 55. |
Assertion (A): A TRIAC is a bidirectional SCR.Reason (R): A TRIAC is a four layers 3 terminal device and can conduct in both directions. |
| A. | Both A and R are correct and R is correct explanation of A |
| B. | Both A and R correct but R is not correct explanation of A |
| C. | A is correct but R is wrong |
| D. | A is wrong but R is correct |
| Answer» B. Both A and R correct but R is not correct explanation of A | |
| 56. |
Ionization potential of mercury is approximately |
| A. | 1 V |
| B. | 2 V |
| C. | 10.4 V |
| D. | 104 V. |
| Answer» D. 104 V. | |
| 57. |
In the ___________ type of chopper, two stage conversions takes place. |
| A. | AC-DC |
| B. | AC link |
| C. | DC link |
| D. | None of the mentioned |
| Answer» B. AC link | |
| 58. |
With increase in firing angle |
| A. | Both harmonic distortion and quality of input current increases |
| B. | Harmonic distortion increases and quality of input current decreases |
| C. | Harmonic distortion decreases and quality of input current increases |
| D. | Both harmonic distortion and quality of input current decreases |
| Answer» C. Harmonic distortion decreases and quality of input current increases | |
| 59. |
Anode of an operational SCR is |
| A. | Always positive w.r.t cathode |
| B. | Always negative w.r.t anode |
| C. | Always positive w.r.t anode |
| D. | Always negative w.r.t cathode |
| Answer» B. Always negative w.r.t anode | |
| 60. |
Choppers is a |
| A. | AC - DC converters |
| B. | AC - AC converters |
| C. | DC - AC converters |
| D. | DC - DC converters |
| Answer» E. | |
| 61. |
A single phase step up cycloconverter changes 50 Hz to 100 Hz.Then one half wave of input will give rise to |
| A. | one half wave of output |
| B. | one full wave of output |
| C. | two full waves of output |
| D. | either (b) or (c) |
| Answer» C. two full waves of output | |
| 62. |
In a mercury arc rectifier the cathode voltage drop is due to |
| A. | surface resistance |
| B. | expenditure of energy in liberating electrons from the mercury |
| C. | expenditure of energy in ionization |
| D. | expenditure of energy in overcoming the electrostatic field. |
| Answer» C. expenditure of energy in ionization | |
| 63. |
For a buck converter to reduce the conduction losses in diode |
| A. | A high on - resistance switch can be added in parallel |
| B. | A low on - resistance switch can be added in parallel |
| C. | A high on - resistance switch can be added in series |
| D. | A low on - resistance switch can be added in series |
| Answer» C. A high on - resistance switch can be added in series | |
| 64. |
The curve between V and I of SCR when anode is positive w.r.t cathode andwhen anode is negative w.r.t cathode are known as |
| A. | both as forward characteristics |
| B. | both as reverse characteristics |
| C. | former as forward characteristics and later as reverse characteristics |
| D. | former as reverse characteristics and later as forward characteristics |
| Answer» D. former as reverse characteristics and later as forward characteristics | |
| 65. |
Voltage commutation circuit can be converted into a current commutationby interchanging the positions of |
| A. | Diode and capacitor |
| B. | Capacitor and SCR |
| C. | Inductor and capacitor |
| D. | Capacitor and load |
| Answer» B. Capacitor and SCR | |
| 66. |
What is the formula for output voltage for Buck-Boost converter? |
| A. | D×Vin |
| B. | Vin ÷ (1-D) |
| C. | D×Vin ÷ (1 |
| Answer» D. | |
| 67. |
Transformer utilization factor is a measure of the merit of a rectifier circuit.It is the ratio of |
| A. | AC input power to the transformer volt - amp rating required by secondary |
| B. | AC input power to the transformer volt - amp rating required by primary |
| C. | DC output power to the transformer volt - amp rating required by secondary |
| D. | DC output power to the transformer volt - amp rating required by primary |
| Answer» D. DC output power to the transformer volt - amp rating required by primary | |
| 68. |
If all the SCR’s of 3 phase PAC is replaced by diodes, they would betriggered |
| A. | 120 degree after the zero crossing of the corresponding line voltages |
| B. | 60 degree after the zero crossing of the corresponding line voltages |
| C. | 120 degree before the zero crossing of the corresponding line voltages |
| D. | 60 degree before the zero crossing of the corresponding line voltages |
| Answer» C. 120 degree before the zero crossing of the corresponding line voltages | |
| 69. |
IGT stands for |
| A. | Insulated gate bipolar transistor |
| B. | Insulated gate bidirectional transistor |
| C. | Inductive gate bipolar transistor |
| D. | Inductive gate bidirectional transistor |
| Answer» C. Inductive gate bipolar transistor | |
| 70. |
As the breakdown voltage reached, the DIAC exhibits |
| A. | Negative resistance characteristics |
| B. | Goes into avalanche condition |
| C. | Voltage drop snaps back |
| D. | All of these |
| Answer» E. | |
| 71. |
A thyristor is reverse biased. A positive gate pulse is applied. Thethyristor |
| A. | will be turned on |
| B. | may or may not turn on |
| C. | will not turn on |
| D. | will turn on after sometime |
| Answer» D. will turn on after sometime | |
| 72. |
In a thyristor, the magnitude of the anode current will: |
| A. | increase if the gate current is increased |
| B. | decrease if the gate current is decreased |
| C. | increase if gate current is decreased |
| D. | no change with the variation of the gate current |
| Answer» E. | |
| 73. |
In three phase cycloconverters, the reduction factor is given by |
| A. | input frequency/output frequency |
| B. | (input frequency/output frequency) -1 |
| C. | (input frequency/output frequency) -1/2 |
| D. | (input frequency/output frequency) 1/ |
| Answer» C. (input frequency/output frequency) -1/2 | |
| 74. |
A thyristor has a turn on time of 6 μs. If the anode circuit isinductive, the turn on time will be |
| A. | 6 μs |
| B. | less than 6μs |
| C. | more than 6 μs |
| D. | either 6 μs or less |
| Answer» D. either 6 μs or less | |
| 75. |
Buck-Boost acts as Buck converter for duty cycle is equal to _________ |
| A. | .9 |
| B. | .7 |
| C. | .6 |
| D. | .4 |
| Answer» E. | |
| 76. |
In a 3 phase full converter the average load current is 150 A.The average thyristor current is |
| A. | 150 A |
| B. | 75A |
| C. | 50 A |
| D. | 25 A |
| Answer» D. 25 A | |
| 77. |
A crowbar is a circuit which is used to protect a |
| A. | voltage sensitive load from excessive dc power supply output voltages |
| B. | current sensitive load from excessive dc power supply output voltages |
| C. | voltage sensitive load from excessive ac power supply output voltages |
| D. | current sensitive load from excessive ac power supply output voltages |
| Answer» B. current sensitive load from excessive dc power supply output voltages | |
| 78. |
In a silicon controlled rectifier, the load is connected |
| A. | Across anode |
| B. | In series with anode |
| C. | Across cathode |
| D. | In series with cathode |
| Answer» C. Across cathode | |
| 79. |
The ac input current at slip rings will be |
| A. | 6.3 A |
| B. | 5.8 A |
| C. | 4.1A |
| D. | 3.8 A. |
| Answer» D. 3.8 A. | |
| 80. |
Unipolar modulation is generally used in |
| A. | AC - AC converters |
| B. | AC - DC converters |
| C. | DC - AC converters |
| D. | DC - DC converters |
| Answer» E. | |
| 81. |
The function of snubber circuit connected across the SCR is to: |
| A. | Suppress dv/dt |
| B. | Increase dv/dt |
| C. | Decrease dv/dt |
| D. | Decrease di/dt |
| Answer» B. Increase dv/dt | |
| 82. |
Which of the following finds application in speed control of a dc motor? |
| A. | FET |
| B. | NPN transistor. |
| C. | SCR. |
| D. | None of the above. |
| Answer» B. NPN transistor. | |
| 83. |
The most suited gate pulses given to the AC regulator with R – L load can be in the form of |
| A. | Continuous signal |
| B. | Large isolating pulse transformer |
| C. | A train of pulses |
| D. | None of these |
| Answer» D. None of these | |
| 84. |
In case of the two-transistor model (T1 & T2) of GTO with anode-short,the anode-short is placed between the |
| A. | emitter of T1 & T2 |
| B. | emitter of T1 & base of T2 |
| C. | emitter of T1 & base of T1 |
| D. | emitter of T1 & collector of T2 |
| Answer» D. emitter of T1 & collector of T2 | |
| 85. |
In a 3 phase full converter, the instantaneous output voltage canhave negative part if |
| A. | firing angle is less than 60° |
| B. | firing angle is less than 90° |
| C. | firing angle is more than 60° |
| D. | firing angle is more than 90° |
| Answer» D. firing angle is more than 90° | |
| 86. |
In thyristor, holding current is: |
| A. | more than the latching current |
| B. | less than the latching current |
| C. | equal to latching current |
| D. | none of the above |
| Answer» C. equal to latching current | |
| 87. |
The input current waveform of a bridge controlled rectifier when theload is perfectly filtered is |
| A. | Sine wave |
| B. | Square wave |
| C. | Saw – tooth wave |
| D. | Trapezoidal wave |
| Answer» C. Saw – tooth wave | |
| 88. |
In a flyback converter, the inductor of the buck-boost converter has beenreplaced by a |
| A. | Flyback capacitor |
| B. | Flyback resistor |
| C. | Flyback transformer |
| D. | Flyback transistor |
| Answer» D. Flyback transistor | |
| 89. |
With gate open, the maximum anode current at which SCR is turned offfrom ON condition is called |
| A. | breakdown voltage |
| B. | peak reverse voltage |
| C. | holding current |
| D. | latching current |
| Answer» E. | |
| 90. |
Under harmonic free load voltages, the 3 phase VSI |
| A. | Does not contains second harmonic |
| B. | Does not contains third harmonic |
| C. | Does not contains fifth harmonic |
| D. | Does not contains seventh harmonic |
| Answer» B. Does not contains third harmonic | |
| 91. |
In a 3 phase half wave rectifier, when firing angle is less than 90 degree,then the average dc output voltage becomes |
| A. | Positive |
| B. | Negative |
| C. | Zero |
| D. | None of these |
| Answer» B. Negative | |
| 92. |
Turn-off time of an SCR is measured from the instant: |
| A. | anode current becomes zero |
| B. | anode voltage becomes zero |
| C. | anode voltage and anode current becomes zero |
| D. | gate current becomes zero |
| Answer» B. anode voltage becomes zero | |
| 93. |
An ideal diode is |
| A. | Unidirectional |
| B. | Bidirectional |
| C. | Fixed voltage polarity |
| D. | Only (a) and (c) |
| Answer» E. | |
| 94. |
The amount of dielectric heating is inversely proportional tofrequency. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» C. none | |
| 95. |
Practical way of obtaining static voltage equalization in series connected SCRs is by the use of: |
| A. | One resistor across the string |
| B. | Resistors of different values across each SCR |
| C. | Resistors of the same value across each SCR |
| D. | One resistor in series with each SCR |
| Answer» D. One resistor in series with each SCR | |
| 96. |
In a three phase converter, the number of notches per cycle is |
| A. | One |
| B. | Three |
| C. | Six |
| D. | Nine |
| Answer» D. Nine | |
| 97. |
A cycloconverter is a: |
| A. | Frequency changer from higher to lower frequency with one-state conversion |
| B. | Frequency changer from higher to lower frequency with two-stage conversion |
| C. | Frequency changer from lower to higher frequency with one-stage conversion |
| D. | Either a or c |
| Answer» E. | |
| 98. |
The single phase mid-point type cycloconverter uses __________ number ofSCRs. |
| A. | 4 |
| B. | 8 |
| C. | 6 |
| D. | none of the mentioned |
| Answer» B. 8 | |
| 99. |
The dc current will be approximately |
| A. | 2.5 A |
| B. | 3 A |
| C. | 3.25 A |
| D. | 3.75 A. |
| Answer» C. 3.25 A | |
| 100. |
A full wave rectifier with resistive load produces |
| A. | Second harmonic |
| B. | Third harmonic |
| C. | Fifth harmonic |
| D. | Do not produce harmonics |
| Answer» E. | |