MCQOPTIONS
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MCQOPTIONS
This section includes 451 Mcqs, each offering curated multiple-choice questions to sharpen your ENGINEERING SERVICES EXAMINATION (ESE) knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
In a full bridge single phase inverter feeding RLC load |
| A. | one thyristor and one diode conduct simultaneously |
| B. | two thyristors conduct simultaneously |
| C. | two thyristors or two diodes conduct simultaneously |
| D. | four thyristors conduct simultaneously |
| Answer» D. four thyristors conduct simultaneously | |
| 52. |
A single phase half wave rectifier circuit has a free wheeling diode. The free wheeling diode will conduct only if |
| A. | load is purely resistive |
| B. | load is purely inductive |
| C. | load is combination of R and L |
| D. | load is purely inductive or combination of R and L |
| Answer» E. | |
| 53. |
UJT can be used for |
| A. | firing an SCR |
| B. | turning off an SCR |
| C. | both firing and turning off an SCR |
| D. | none of the above |
| Answer» B. turning off an SCR | |
| 54. |
The specified maximum junction temperature of thyristors is about |
| A. | 50°C |
| B. | 80°C |
| C. | 120°C |
| D. | 200°C |
| Answer» D. 200°C | |
| 55. |
In sinusoidal PWM for inverters the width of different pulses are not the same. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 56. |
Assertion (A): A high dv/dt may cause triggering of a thyristor.Reason (R): A high dv/dt results in charging current in the thyristor. |
| 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 | |
| 57. |
A cycloconverter cannot give a frequency higher than input frequency. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 58. |
The number of leads in an SCR are : |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 5 |
| Answer» C. 4 | |
| 59. |
A cycloconverter for single phase operation has |
| A. | one positive group and one negative group converters |
| B. | two positive group and two negative group converters |
| C. | three positive group and three negative group converters |
| D. | any of the above |
| Answer» B. two positive group and two negative group converters | |
| 60. |
A single phase semiconverter has a freewheeling diode. If the firing angle is α and the load is purely resistive, the periods of conduction and freewheeling respectively are |
| A. | π - α and 0 |
| B. | π - α and α |
| C. | π + α and 0 |
| D. | π + α and α |
| Answer» B. π - α and α | |
| 61. |
A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be |
| A. | about 1350 rpm |
| B. | about 720 rpm |
| C. | about 360 rpm |
| D. | either (b) or (c) |
| Answer» C. about 360 rpm | |
| 62. |
A cycloconverter is a group of controlled rectifiers. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 63. |
In the basic series inverter circuit, the source current has |
| A. | low harmonic content |
| B. | high harmonic content |
| C. | low or high harmonic content depending on firing angle |
| D. | zero harmonic content |
| Answer» C. low or high harmonic content depending on firing angle | |
| 64. |
A 3 phase semiconverter when supplying a certain load has a rectification efficiency of 0.6 and transformer utilisation factor of 0.35. When a 3 phase full converter is supplying the same load |
| A. | rectification efficiency will be more than 0.6 and TUF will be more than 0.35 |
| B. | rectification efficiency will be more than 0.6 but TUF will be less than 0.35 |
| C. | rectification efficiency will be less than 0.6 and TUF will be less than 0.35 |
| D. | rectification efficiency will be less than 0.6 but TUF will be more than 0.35 |
| Answer» B. rectification efficiency will be more than 0.6 but TUF will be less than 0.35 | |
| 65. |
On load tap changer using thyristors can have a maximum of two taps. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 66. |
In integral cycle control of ac regulators, the period of integral cycle control, i.e., (m + n) T should be |
| A. | less than mechanical or thermal time constant of the system |
| B. | more than the mechanical or thermal time constant of the system |
| C. | more or less than the mechanical or thermal time constant |
| D. | very high |
| Answer» B. more than the mechanical or thermal time constant of the system | |
| 67. |
A single phase semiconverter is supplying RLE load and has a freewheeling diode across the load. The firing angle is α. The freewheeling diode conducts for |
| A. | α° in each half cycle |
| B. | (π - α)° in each cycle |
| C. | α° in one full cycle |
| D. | (π + α)° in each half cycle |
| Answer» B. (π - α)° in each cycle | |
| 68. |
Which of the following devices has metal-silicon junction? |
| A. | General purpose power diode |
| B. | Schottky diode |
| C. | SCR |
| D. | MOSFET |
| Answer» C. SCR | |
| 69. |
In thermal ohm's law, temperature and power loss are analogous to |
| A. | V and I respectively of ohm's law |
| B. | I and V respectively of ohm's law |
| C. | R and V respectively of ohm's law |
| D. | I and R respectively of ohm's law |
| Answer» C. R and V respectively of ohm's law | |
| 70. |
Mc Murray full bridge inverter uses |
| A. | 4 thyristors and 2 diodes |
| B. | 4 thyristors and 4 diodes |
| C. | 8 thyristors and 4 diodes |
| D. | 8 thyristors and 8 diodes |
| Answer» D. 8 thyristors and 8 diodes | |
| 71. |
Which of these commutation methods uses an auxiliary SCR? |
| A. | Class A |
| B. | Class B |
| C. | Class C |
| D. | Class D |
| Answer» D. Class D | |
| 72. |
A separately excited dc motor is run from a dc source through a chopper. At 600 rpm and rated torque, the duty cycle of chopper is 0.8. At 600 rpm and half the rated torque, the duty cycle is likely to be |
| A. | 0.9 |
| B. | 0.8 |
| C. | 0.75 |
| D. | 0.6 |
| Answer» D. 0.6 | |
| 73. |
A UJT exhibits negative resistance characteristics when |
| A. | Current is less than valley current |
| B. | Current is less than peak current |
| C. | Current is more than peak current but less than valley current |
| D. | None of the above |
| Answer» D. None of the above | |
| 74. |
Assertion (A): Inverters and choppers use fast switching thyristors Reason (R): Fast switching SCR has low turn off time. |
| 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 | |
| 75. |
In single phase half wave regulator, the average current over one full cycle |
| A. | is always positive |
| B. | may be positive or negative |
| C. | may be negative |
| D. | is always negative |
| Answer» E. | |
| 76. |
Assertion (A): The output voltage of an inverter can be controlled by PWM techniqueReason (R): In a current source inverter the input current is constant. |
| 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» C. A is correct but R is wrong | |
| 77. |
In a thyristor the gate current is increased, then |
| A. | anode current will increase |
| B. | anode current will decrease |
| C. | anode current will remain constant |
| D. | anode current may increase or decrease |
| Answer» D. anode current may increase or decrease | |
| 78. |
A high frequency series inverter consists of |
| A. | a number of series inverters in series |
| B. | a number of series inverters in parallel |
| C. | a number of parallel inverters in parallel |
| D. | a number of parallel inverters in series |
| Answer» C. a number of parallel inverters in parallel | |
| 79. |
In a thyristor the gate lead is connected to the n layer near the p layer to which anode is connected. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 80. |
In a 3 phase full converter feeding a highly inductive load, the average load current is 150 A. The peak current through thyristor is |
| A. | 150 A |
| B. | 75 A |
| C. | 50 A |
| D. | 300 A |
| Answer» B. 75 A | |
| 81. |
The characteristics of which device has peak point and valley point |
| A. | SCR |
| B. | PUT |
| C. | SCS |
| D. | Shockley diode |
| Answer» C. SCS | |
| 82. |
A single phase full converter gives maximum and minimum output voltage at firing angles of |
| A. | 0 and 180° respectively |
| B. | 180° and 0° respectively |
| C. | 0 and 90° respectively |
| D. | 90° and 0° respectively |
| Answer» B. 180° and 0° respectively | |
| 83. |
In auxiliary commutated chopper, the peak value of thyristor current is |
| A. | equal to peak value of load current |
| B. | equal to peak value of capacitor current |
| C. | sum of peak value of load current and capacitor current |
| D. | none of the above |
| Answer» D. none of the above | |
| 84. |
The gate lead, in a thyristor is welded to : |
| A. | p layer to which anode is connected |
| B. | n layer nearest to the anode terminal |
| C. | p layer nearest to the cathode terminal |
| D. | outside n layer |
| Answer» C. p layer nearest to the cathode terminal | |
| 85. |
A dc separately excited motor has a constant field current. The armature is fed from a single phase supply through a semi-converter. When α = 0, speed is 600 rpm. If α = 90°, the speed is likely to be |
| A. | about 300 rpm |
| B. | about 150 rpm |
| C. | about 75 rpm |
| D. | about zero |
| Answer» B. about 150 rpm | |
| 86. |
Induction heating systems require low frequency inverters. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 87. |
In a single phase semiconverter feeding a highly inductive load, the load current is |
| A. | sinusoidal |
| B. | nearly constant |
| C. | absolutely constant |
| D. | rectangular |
| Answer» C. absolutely constant | |
| 88. |
A single phase fully controlled bridge converter is feeding an RLE load. Input voltage is Vm sin ωt and firing angle is α. If average current is I₀, then |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 89. |
A single phase half wave converter is used to charge a battery of 50 V. The thyristor is continuously fired by dc signal. Input voltage is v = Vm sin ωt. The thyristor will conduct |
| A. | from 0 to 180° |
| B. | when v > 50 V |
| C. | from 0 to 90° |
| D. | When v < 50 V |
| Answer» C. from 0 to 90° | |
| 90. |
The characteristics of a non-linear resistance is i = kv⁴. If i becomes 100 times, v becomes |
| A. | about 100 times |
| B. | about 10 times |
| C. | about 3 times |
| D. | about twice |
| Answer» D. about twice | |
| 91. |
A chopper |
| A. | converts constant voltage dc into ac and then into variable voltage dc |
| B. | converts constant voltage dc into variable voltage dc directly |
| C. | converts ac of one frequency into ac of another frequency |
| D. | converts ac to dc |
| Answer» C. converts ac of one frequency into ac of another frequency | |
| 92. |
A single phase full converter can operate in |
| A. | 4 quadrants |
| B. | 3 quadrants |
| C. | 2 quadrants |
| D. | 1 quadrant |
| Answer» D. 1 quadrant | |
| 93. |
An SUS is |
| A. | exactly similar to SCR but with higher rating |
| B. | similar to UJT |
| C. | PUT and avalanche diode connected in anti parallel |
| D. | SCR and avalanche diode connected in parallel |
| Answer» D. SCR and avalanche diode connected in parallel | |
| 94. |
In brushless excitation system of modern alternators, the main exciter is |
| A. | dc generator |
| B. | ac generator |
| C. | either dc or ac generator |
| D. | induction generator |
| Answer» C. either dc or ac generator | |
| 95. |
Which of the following devices exhibit negative resistance characteristics? |
| A. | UJT |
| B. | PUT |
| C. | Both UJT and PUT |
| D. | UJT, PUT and SBS |
| Answer» D. UJT, PUT and SBS | |
| 96. |
The total number of leads in reverse conducting thyristor is |
| A. | 2 |
| B. | 3 |
| C. | 1 |
| D. | 4 |
| Answer» C. 1 | |
| 97. |
A 3 phase series inverter has |
| A. | 12 thyristors |
| B. | 6 thyristors |
| C. | 3 thyristors |
| D. | 3 or 6 thyristors |
| Answer» C. 3 thyristors | |
| 98. |
Natural commutation can be used in : |
| A. | DC circuits only |
| B. | AC circuits only |
| C. | both AC and DC circuits |
| D. | none of the above |
| Answer» C. both AC and DC circuits | |
| 99. |
Two thyristors of the same rating and specifications |
| A. | will have equal on state voltage drops |
| B. | will have equal forward blocking voltage for the same current |
| C. | will have different on state voltage drops |
| D. | may have equal or different on state voltage drops and equal or different forward blocking voltage's for the same current |
| Answer» E. | |
| 100. |
Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V. Reason (R): When an SCR is conducting, the junction temperature is about 200°C. |
| 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» D. A is wrong but R is correct | |