MCQOPTIONS
Saved Bookmarks
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.
| 201. |
A single phase half wave regulator uses |
| A. | 2 diodes and 2 thyristors |
| B. | 2 thyristors |
| C. | 1 diode and 1 thyristor |
| D. | 2 diodes |
| Answer» D. 2 diodes | |
| 202. |
In a full bridge inverter, the waveshape of load current depends on |
| A. | relative values of load parameters R, L and C |
| B. | relative values of load parameters R and L |
| C. | relative values of load parameters L and C |
| D. | gating frequency |
| Answer» B. relative values of load parameters R and L | |
| 203. |
A reactor is used in a dual converter operating in non-circulating current mode. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 204. |
A relaxation oscillator uses |
| A. | tunnel diode |
| B. | UJT |
| C. | both tunnel diode and UJT |
| D. | PIN diode |
| Answer» C. both tunnel diode and UJT | |
| 205. |
A single phase half wave rectifier is feeding a resistive load. As firing angle is increased |
| A. | dc output voltage and rms output voltage decrease in the same proportion |
| B. | dc output voltage and rms output voltage decrease |
| C. | dc output voltage and rms output voltage increase |
| D. | dc output voltage and rms output voltage increase in the same proportion |
| Answer» C. dc output voltage and rms output voltage increase | |
| 206. |
An SCR has a turn on time of 4 μs. The gate pulse should have a duration of about |
| A. | 2 μs |
| B. | 5 μs |
| C. | 20 μs |
| D. | 50 μs |
| Answer» C. 20 μs | |
| 207. |
The two-transistor model of a thyristor consists of two transistors : |
| A. | one n-p-n and other p-n-p |
| B. | both p-n-p |
| C. | both n-p-n |
| D. | one n-p-n and other UJT |
| Answer» B. both p-n-p | |
| 208. |
In a semi converter feeding a resistive load, |
| A. | the waveshapes of input voltage and input current are always similar |
| B. | the waveshapes of input voltage and input current can never be similar |
| C. | the waveshapes of input voltage and input current are similar only if firing angle is zero |
| D. | the waveshapes of input voltage and input current are similar only if firing angle is high |
| Answer» D. the waveshapes of input voltage and input current are similar only if firing angle is high | |
| 209. |
When the core of a saturable reactor is saturated, the inductance is high. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 210. |
In disc mounting of SCR |
| A. | SCR is clamped on one side of disc shaped heat sink |
| B. | SCR is clamped between two disc shaped heat sinks |
| C. | The SCR has low current rating |
| D. | None of the above |
| Answer» C. The SCR has low current rating | |
| 211. |
In a dual converter operated in circulating current mode, the circulating current flows |
| A. | when load current is zero |
| B. | when load current is non-zero |
| C. | even when load current is zero |
| D. | none of the above |
| Answer» D. none of the above | |
| 212. |
A class B chopper operates in third quadrant. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 213. |
In a full bridge circuit supplying an RLC under damped circuit |
| A. | the waveshapes of output voltage and load current are square |
| B. | the waveshapes of output voltage and load current are sinusoidal |
| C. | the waveshapes of output voltage is square but the waveshape of load current is nearly sinusoidal |
| D. | none of the above |
| Answer» D. none of the above | |
| 214. |
When an SCR is reverse biased |
| A. | two junctions are reverse biased and one junction is forward biased. |
| B. | all the three junctions are reverse biased. |
| C. | one junction is reverse biased and two junctions are forward biased. |
| D. | any of the above depending on the magnitude of reverse bias. |
| Answer» B. all the three junctions are reverse biased. | |
| 215. |
A dc series motor is coupled to a load whose torque is proportional to speed. It is fed by a single phase ac supply through a full converter. When speed is 500 rpm, firing angle is 45°. It is desired to raise the speed. It will be necessary to |
| A. | decrease the firing angle |
| B. | increase the firing angle |
| C. | either decrease or increase the firing angle depending on the required speed |
| D. | decrease the load torque |
| Answer» B. increase the firing angle | |
| 216. |
A LASCR has |
| A. | 4 semiconductor layers and 3 junctions |
| B. | 3 semiconductor layers and 2 junctions |
| C. | 2 semiconductor layers and 2 junctions |
| D. | any of these depending on the rating |
| Answer» B. 3 semiconductor layers and 2 junctions | |
| 217. |
In a modified series inverter |
| A. | the maximum output frequency is less than frequency of damped oscillations |
| B. | the output frequency can be even higher than the frequency of damped oscillations |
| C. | the output frequency cannot exceed the frequency of damped oscillations |
| D. | any of the above |
| Answer» C. the output frequency cannot exceed the frequency of damped oscillations | |
| 218. |
In Jone chopper, the commutating element |
| A. | is a capacitor |
| B. | is a capacitor and an inductor |
| C. | is a capacitor and an auto transformer |
| D. | none of the above |
| Answer» D. none of the above | |
| 219. |
The number of layers in a Shockley diode are |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 2 or 3 |
| Answer» D. 2 or 3 | |
| 220. |
In a modified series inverter with two inductors and two capacitors, the load current |
| A. | has 2 parallel paths |
| B. | has only one parallel path |
| C. | can have three parallel paths |
| D. | has four parallel paths |
| Answer» B. has only one parallel path | |
| 221. |
In a single phase half wave ac regulator feeding a resistive load, the rms load current |
| A. | is always positive |
| B. | may be positive or negative |
| C. | is always negative |
| D. | can be even zero |
| Answer» B. may be positive or negative | |
| 222. |
Forward dv/dt rating of an SCR is |
| A. | the maximum rate of rise of anode voltage which will trigger the SCR |
| B. | the maximum rate of rise of anode voltage which will not trigger the SCR if gate signal is applied |
| C. | the maximum rate of rise of anode voltage which will not trigger the SCR if gate signal is not applied |
| D. | either (b) or (c) |
| Answer» D. either (b) or (c) | |
| 223. |
Thyristors can be used for control of |
| A. | dc separately excited motor |
| B. | dc shunt motor |
| C. | dc series motor |
| D. | all of the above |
| Answer» E. | |
| 224. |
A crowbar circuit is generally needed for protection under fault conditions. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 225. |
The number of leads in a DIAC are |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 6 |
| Answer» B. 3 | |
| 226. |
A single phase dual converter consists of |
| A. | two fully controlled converters connected in parallel |
| B. | two fully controlled converters connected in antiparallel |
| C. | two fully controlled semiconverters connected in antiparallel |
| D. | two fully controlled semiconverters connected in parallel |
| Answer» C. two fully controlled semiconverters connected in antiparallel | |
| 227. |
The snubber circuit consists of |
| A. | a capacitor connected in series with thyristor |
| B. | a capacitor connected in parallel with thyristor |
| C. | a resistor and capacitor in series connected across thyristor |
| D. | none of the above |
| Answer» D. none of the above | |
| 228. |
The method of triggering SCS is |
| A. | application of positive pulse at cathode gate or negative pulse at anode gate |
| B. | application of pulse at anode gate |
| C. | application of pulse at cathode gate |
| D. | application of low voltage at anode |
| Answer» B. application of pulse at anode gate | |
| 229. |
Assertion (A): A class C chopper can operate in first and second quadrants Reason (R): A class B chopper operates only in second quadrant. |
| 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 | |
| 230. |
The effect of source inductance in a 3 phase fully controlled bridge converter is to |
| A. | decrease the output voltage |
| B. | increase the output voltage |
| C. | decrease the output voltage and increase the output current |
| D. | increase the output voltage and decrease the output current |
| Answer» B. increase the output voltage | |
| 231. |
A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torque |
| A. | will be less than 100 N-m |
| B. | will be more than 100 N-m |
| C. | may be more or less than 100 N-m depending on motor parameters |
| D. | very small |
| Answer» C. may be more or less than 100 N-m depending on motor parameters | |
| 232. |
When a power diode is conducting, the voltage drop across it is about |
| A. | I V |
| B. | 5 V |
| C. | 20 V |
| D. | 50 V |
| Answer» B. 5 V | |
| 233. |
In a single phase full wave controlled rectifier using centre tap transformer, the voltage across each half of secondary is Vm sin ωt. The peak inverse voltage is |
| A. | 2 Vm |
| B. | Vm |
| C. | 0.5 Vm |
| D. | 0.25 Vm |
| Answer» B. Vm | |
| 234. |
The average load current supplied by a thyristor depends on |
| A. | firing angle |
| B. | firing frequency |
| C. | magnitude of gate current |
| D. | all of the above |
| Answer» B. firing frequency | |
| 235. |
In a 3 phase full wave regulator feeding resistance load connected in star, the possible range of firing angle α is |
| A. | 0 ≤ α ≤ 180° |
| B. | 0 ≤ α ≤ 150° |
| C. | 0 ≤ α ≤ 120° |
| D. | 0 ≤ α ≤ 90° |
| Answer» C. 0 ≤ α ≤ 120° | |
| 236. |
A step down cycloconverter has an input frequency f. If it uses natural commutation, the output frequency |
| A. | must be a sub-multiple of input frequency |
| B. | can be any frequency |
| C. | must be an even sub-multiple of input frequency |
| D. | must be an odd sub-multiple of input frequency |
| Answer» B. can be any frequency | |
| 237. |
Assertion (A): Thyristors can be used in controlled heating, excitation systems of alternators, speed control of motors and HVDCReason (R): A static var system using thyristors is very commonly used in high voltage ac systems. |
| 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 | |
| 238. |
Assertion (A): A GTO can be turned on and turned off by gate pulses Reason (R): A GTO can be turned off by negative gate pulse. |
| 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 | |
| 239. |
An electric heater is controlled by thyristors through on-off control. If α = 0.4, the heating is |
| A. | 16% maximum |
| B. | 40% of maximum |
| C. | 60% of maximum |
| D. | 84% of maximum |
| Answer» C. 60% of maximum | |
| 240. |
In a bridge inverter with single pulse width modulation |
| A. | the output frequency is equal to frequency of reference signal |
| B. | the output frequency is equal to frequency of control signal |
| C. | either (a) or (b) |
| D. | neither (a) nor (b) |
| Answer» B. the output frequency is equal to frequency of control signal | |
| 241. |
A thyristor has a turn on time of 6 μs. If the anode circuit is inductive, 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 | |
| 242. |
A single phase series converter is used for |
| A. | high voltage output |
| B. | high current output |
| C. | high voltage and high current output |
| D. | improving the circuit efficiency |
| Answer» B. high current output | |
| 243. |
Assertion (A): A cycloconverter may be line commutated or forced commutatedReason (R): A step up cycloconverter requires forced commutation. |
| 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 | |
| 244. |
In a 3 phase bridge inverter, the gating signals for the three phases have a phase difference of |
| A. | 120° |
| B. | 60° |
| C. | 240° |
| D. | any of the above |
| Answer» B. 60° | |
| 245. |
The factor η for a UJT is about |
| A. | 0.1 |
| B. | 0.2 |
| C. | 0.6 |
| D. | 0.9 |
| Answer» D. 0.9 | |
| 246. |
In a stud mounted SCR, the stud is |
| A. | in thermal contact with heat sink |
| B. | insulated from heat sink |
| C. | in electrical and thermal contact with heat sink |
| D. | in either electrical or thermal contact with heat sink |
| Answer» D. in either electrical or thermal contact with heat sink | |
| 247. |
Which chopper circuit operates in all the 4 quadrants? |
| A. | A |
| B. | C |
| C. | D |
| D. | E |
| Answer» E. | |
| 248. |
A step up chopper can give an output voltage |
| A. | higher than input voltage |
| B. | lower than input voltage |
| C. | both higher and lower input voltage |
| D. | all of the above |
| Answer» B. lower than input voltage | |
| 249. |
A single phase full wave regulator feeds a resistive load. The firing angle of thyristors is 90°. The input power factor is |
| A. | 1 |
| B. | 0.707 lagging |
| C. | 0.5 lagging |
| D. | 0.2 lagging |
| Answer» C. 0.5 lagging | |
| 250. |
A single phase half wave converter is feeding a resistive load. Output dc power is Pdc and total power delivered to load is Pac then |
| A. | Pdc = Pac for all values of firing angles |
| B. | Pdc = Pac if firing angle is less than 180° |
| C. | Pdc < Pac for all values of firing angles |
| D. | Pdc < Pac if firing angle is less than 180° |
| Answer» E. | |