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.
| 251. |
In a multiphase chopper, the different choppers operate in |
| A. | series and all simultaneously |
| B. | parallel and one at a time |
| C. | parallel and simultaneously |
| D. | either (b) or (c) |
| Answer» C. parallel and simultaneously | |
| 252. |
In a single phase half wave converter feeding resistive load and full wave converter (M - 2 connection) feeding a resistive load the circuit conditions are similar. The firing angle is α. Then the waveshapes of voltages across thyristors |
| A. | are similar |
| B. | are not similar |
| C. | may be similar or dissimilar |
| D. | are similar only for some values of α |
| Answer» B. are not similar | |
| 253. |
A dc separately excited motor has constant field current. The armature is fed from a single phase supply through a full converter. When α = 0, speed is 500 rpm. If α = 45°, the speed is likely to be |
| A. | about 350 rpm |
| B. | about 250 rpm |
| C. | about 175 rpm |
| D. | about 125 rpm |
| Answer» E. | |
| 254. |
When a thyristor is conducting, the voltage drop across it is about |
| A. | 1 V |
| B. | 10 V |
| C. | 100 V |
| D. | 0.1 V |
| Answer» B. 10 V | |
| 255. |
To turn off an SCR, it is necessary to reduce its current to less than : |
| A. | trigger current |
| B. | holding current |
| C. | breakover current |
| D. | none of the above |
| Answer» C. breakover current | |
| 256. |
When a single phase dual converter is operating in circulating current mode |
| A. | both converters are working as rectifiers simultaneously |
| B. | one converter is always working as rectifier and the other as inverter |
| C. | only one converter is working at one time |
| D. | both converters are either working as rectifiers or as inverters simultaneously |
| Answer» C. only one converter is working at one time | |
| 257. |
Assertion (A): Light triggering is very suitable for HVDC transmission.Reason (R): Light triggering has the advantage of complete electrical isolation of gate circuit. |
| 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 | |
| 258. |
Class A and class B chopper |
| A. | operate in first quadrant |
| B. | operate in second quadrant |
| C. | class A chopper operates in first quadrant while class B operates in second quadrant |
| D. | may operate in either first or second quadrant |
| Answer» D. may operate in either first or second quadrant | |
| 259. |
In load commutated chopper, the commutating element |
| A. | is capacitor |
| B. | is capacitor and inductor |
| C. | is capacitor, inductor and auxiliary thyristor |
| D. | any of the above depending on load |
| Answer» B. is capacitor and inductor | |
| 260. |
A class D chopper |
| A. | can operate in first quadrant only |
| B. | can operate in second quadrant only |
| C. | can operate in either first or fourth quadrant |
| D. | can operate in all the quadrants |
| Answer» D. can operate in all the quadrants | |
| 261. |
If we connect two silicon unilateral switches in anti- parallel we get |
| A. | SCR |
| B. | SBS |
| C. | SCS |
| D. | UJT |
| Answer» C. SCS | |
| 262. |
In a single phase dual converter, α1, and α2 are firing angles of the two converters. Then |
| A. | α1 - α2 = π/2 |
| B. | α1 + α2 = π |
| C. | α1 - α2 = π |
| D. | α1 + α2 = π/2 |
| Answer» C. α1 - α2 = π | |
| 263. |
Which statement is correct? |
| A. | BJT and MOSFET are current controlled devices |
| B. | BJT is voltage controlled and MOSFET is current controlled device |
| C. | BJT and MOSFET are voltage controlled devices |
| D. | BJT is current controlled and MOSFET is voltage controlled device |
| Answer» E. | |
| 264. |
A single phase half wave rectifier is feeding a resistive load. When α = 0, dc output voltage is 127 V. When α = 30°, the dc output voltage will be about |
| A. | 127 V |
| B. | 120 V |
| C. | 110 V |
| D. | 100 V |
| Answer» C. 110 V | |
| 265. |
A thyristor circuit is feeding an R-L load. The turn on time can be reduced by |
| A. | decreasing R |
| B. | decreasing L |
| C. | increasing L |
| D. | decreasing R and L together |
| Answer» C. increasing L | |
| 266. |
An SCR is triggered at 80° in the positive half cycle, only. The rms anode current is 25 A. If the firing angle is changed to 160°, the rms current is likely to be |
| A. | 25 A |
| B. | 12.5 A |
| C. | less than 25 A |
| D. | less than 12.5 A |
| Answer» E. | |
| 267. |
In a semi converter feeding a resistive load |
| A. | the waveshapes of output voltage and output current are exactly similar |
| B. | the waveshapes of output voltage and output current can not be similar |
| C. | the waveshapes of output voltage and output current are similar only for low values of firing angle |
| D. | the waveshapes of output voltage and output current may be similar or dissimilar |
| Answer» B. the waveshapes of output voltage and output current can not be similar | |
| 268. |
The total number of leads in SCR, DIAC and TRIAC respectively are |
| A. | 3, 2, 3 |
| B. | 2, 3, 3 |
| C. | 3, 3, 2 |
| D. | 3, 2, 4 |
| Answer» B. 2, 3, 3 | |
| 269. |
In an n stage high frequency series inverter having a time period T, each stage is active for a time interval of |
| A. | T |
| B. | T/n |
| C. | 2T/n |
| D. | T/√n |
| Answer» C. 2T/n | |
| 270. |
As compared to a p-n junction diode |
| A. | a schottky diode has lower cut in voltage and lower reverse saturation current |
| B. | a schottky diode has higher cut in voltage and higher reverse saturation current |
| C. | a Schottky diode has lower cut in voltage and higher reverse saturation current |
| D. | a schottky diode has higher cut in voltage and lower reverse saturation current |
| Answer» D. a schottky diode has higher cut in voltage and lower reverse saturation current | |
| 271. |
In a 3 phase semiconverter, the output voltage becomes discontinuous for |
| A. | firing angle > 30° |
| B. | firing angle > 60° |
| C. | firing angle > 90° |
| D. | firing angle > 120° |
| Answer» C. firing angle > 90° | |
| 272. |
An ideal rectifier should have |
| A. | 100% efficiency, zero ripple factor, zero harmonic factor and unity displacement factor |
| B. | 100% efficiency, zero tipple factor, zero harmonic factor and zero displacement factor |
| C. | 100% efficiency, zero ripple factor, unity harmonic factor and unity displacement factor |
| D. | 100% efficiency, unity ripple factor, zero harmonic factor and unity displacement factor |
| Answer» B. 100% efficiency, zero tipple factor, zero harmonic factor and zero displacement factor | |
| 273. |
When thyristors are connected in parallel, the current distribution may become non-uniform due to |
| A. | inductive effect of current carrying conductors |
| B. | capacitive effect of current carrying conductors |
| C. | both inductive and capacitive effects |
| D. | none of the above |
| Answer» B. capacitive effect of current carrying conductors | |
| 274. |
In a bridge inverter |
| A. | an output transformer is essential |
| B. | an output transformer is not essential |
| C. | an output transformer cannot be connected |
| D. | an output transformer, if used, can improve the efficiency of the circuit |
| Answer» C. an output transformer cannot be connected | |
| 275. |
In integral cycle control of ac regulator, the input power factor is equal to |
| A. | duty cycle α |
| B. | α² |
| C. | √α |
| D. | (α)^1/3 |
| Answer» D. (α)^1/3 | |
| 276. |
McMurrary full bridge inverter uses |
| A. | auxiliary commutation |
| B. | complementary commutation |
| C. | natural commutation |
| D. | any of the above |
| Answer» B. complementary commutation | |
| 277. |
The application of gate signal decreases the break over voltage of on SCR. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 278. |
A fully controlled bridge converter feeds a highly inductive load such that the load current can be assumed to be constant. The wave shape of input current is |
| A. | dc |
| B. | sinusoidal |
| C. | rectangular |
| D. | none of the above |
| Answer» D. none of the above | |
| 279. |
A static excitation system uses |
| A. | transformer and thyristors |
| B. | transformer and ac exciter |
| C. | dc exciter and ac exciter |
| D. | transformer and dc exciter |
| Answer» B. transformer and ac exciter | |
| 280. |
A dc chopper is feeding an RLE load. The condition for maximum ripple is |
| A. | α = 1 |
| B. | α = 0.8 |
| C. | α = 0.5 |
| D. | α < 0.5 |
| Answer» B. α = 0.8 | |
| 281. |
The circuit in figure is for |
| A. | resonant commutation |
| B. | line commutation |
| C. | auxiliary commutation |
| D. | complementary commutation |
| Answer» E. | |
| 282. |
A rectifier is fed by a transformer. The rms voltage and current at secondary of transformer are Vs and Is. Output dc power is Vdc Idc and output ac power is (Vrms ) (Irms), Transformer utilisation factor TUF is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 283. |
The duty cycle of a step down chopper is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 284. |
A fully controlled bridge converter is feeding an RLE load. The load current is I₀. The input voltage is Vm sin ωt. The KVL equation to find firing angle α is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 285. |
For a single phase half wave converter feeding a resistive load, the firing angle a. The waveshape in below figure is for |
| A. | output voltage |
| B. | input voltage |
| C. | voltage drop across thyristor |
| D. | none of the above |
| Answer» E. | |
| 286. |
In a parallel inverter the turn off time tq of thyristor and values of commutating elements L and C are related as |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 287. |
In a half bridge inverter circuit fed by a battery of voltage V, the rms value of fundamental component of output voltage is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 288. |
If peak value of input voltage is Vm and firing angle is α, the average output voltage for single phase half wave and single phase full wave regulators are |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 289. |
Which of the following commutation methods is the overall circuit under damped? |
| A. | Class A |
| B. | Class B |
| C. | Class C |
| D. | Both class A and Class B |
| Answer» E. | |
| 290. |
A 3 phase dual converter consists of |
| A. | two 3 phase semiconverters connected in parallel |
| B. | two 3 phase semiconverters connected in antiparallel |
| C. | two 3 phase full converters connected in antiparallel |
| D. | two 3 phase full converters connected in parallel |
| Answer» D. two 3 phase full converters connected in parallel | |
| 291. |
The symbol in figure is for |
| A. | SUS |
| B. | SBS |
| C. | SCS |
| D. | Shockley diode |
| Answer» C. SCS | |
| 292. |
In a parallel inverter |
| A. | each thyristor is turned on twice during each cycle |
| B. | each thyristor is turned on once during each cycle |
| C. | each thyristor is turned on either once or twice in each load cycle |
| D. | each thyristor may be turned on upto four times in each load cycle |
| Answer» B. each thyristor is turned on once during each cycle | |
| 293. |
Which inverter circuit uses coupled inductors? |
| A. | Modified McMurray full bridge inverter |
| B. | McMurray Bedford half bridge inverter |
| C. | Modified McMurray Bedford half bridge inverter |
| D. | Both (b) and (c) |
| Answer» E. | |
| 294. |
Multiphase choppers are used in |
| A. | low power circuits |
| B. | high power circuit |
| C. | both low and high power circuits |
| D. | medium power circuits |
| Answer» C. both low and high power circuits | |
| 295. |
In a 3 phase bridge inverter with 180° mode of operation the numbers of thyristors conducting at one time are |
| A. | 1 |
| B. | 2 |
| C. | 3 |
| D. | 4 |
| Answer» D. 4 | |
| 296. |
In a 3 phase semiconverter, the firing frequency is |
| A. | equal to line frequency |
| B. | 3 times the line frequency |
| C. | 6 times the line frequency |
| D. | 12 times the line frequency |
| Answer» C. 6 times the line frequency | |
| 297. |
In an SCR, the anode current is controlled by |
| A. | gate current only |
| B. | external circuit only |
| C. | both gate current and external circuit |
| D. | none of the above |
| Answer» C. both gate current and external circuit | |
| 298. |
Present day HVDC converters are all |
| A. | 3 pulse converters |
| B. | 6 pulse converters |
| C. | 12 pulse converters |
| D. | either 6 pulse or 12 converters |
| Answer» D. either 6 pulse or 12 converters | |
| 299. |
For a BJT, α = 0.98, then β = |
| A. | 0.02 |
| B. | 0.5 |
| C. | 4.9 |
| D. | 49 |
| Answer» E. | |
| 300. |
If duty cycle is a and the load is α resistance R, the rms value of output voltage is |
| A. | αV |
| B. | √α V |
| C. | α²V |
| D. | αV/R |
| Answer» C. α²V | |