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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.
| 151. |
A dc chopper is feeding an RLE load. The current can become discontinuous if |
| A. | R/L is high |
| B. | α is low |
| C. | E is high |
| D. | none of the above |
| Answer» E. | |
| 152. |
A TRIAC is equivalent to |
| A. | two thyristors in series |
| B. | two thyristors in parallel |
| C. | one thyristor and one diode |
| D. | one thyristor and one transistor |
| Answer» C. one thyristor and one diode | |
| 153. |
The number of thyristors in a single phase fully controlled bridge rectifier is |
| A. | 16 |
| B. | 8 |
| C. | 4 |
| D. | 2 |
| Answer» D. 2 | |
| 154. |
In a fully controlled bridge converter feeding a resistive load the waveshapes of output voltage and output current |
| A. | are always similar |
| B. | can never be similar |
| C. | may be similar or dissimilar |
| D. | are similar only if α = 0 |
| Answer» B. can never be similar | |
| 155. |
All other parameters remaining the same, a 3 phase bridge inverter with 180° mode of operation |
| A. | has the same peak thyristor current as in 120° mode of operation |
| B. | has higher peak thyristor current than in 120° mode of operation |
| C. | has lower peak thyristor current than in 120° mode of operation |
| D. | any of the above |
| Answer» C. has lower peak thyristor current than in 120° mode of operation | |
| 156. |
When an SCR is in forward blocking mode, the applied voltage |
| A. | appears across only one junction |
| B. | is equally shared by two junctions |
| C. | is equally shared by three junctions |
| D. | may appear across one or more junctions |
| Answer» B. is equally shared by two junctions | |
| 157. |
A surge voltage |
| A. | has very high magnitude and very long duration |
| B. | has very high magnitude and very small duration |
| C. | has very high magnitude and very small duration and can be positive or negative |
| D. | can be only positive |
| Answer» D. can be only positive | |
| 158. |
In a full wave converter (M - 2 connection) feeding an RLE load, the peak thyristor current is 15 A. For fully controlled bridge circuit and same load current, the peak thyristor current will be |
| A. | 30 A |
| B. | 15√2 A |
| C. | 15 A |
| D. | 15/√2 A |
| Answer» D. 15/√2 A | |
| 159. |
In an SCR, the anode current consists of |
| A. | only holes |
| B. | only electrons |
| C. | both electrons and holes |
| D. | either electrons or holes |
| Answer» D. either electrons or holes | |
| 160. |
The dynamic equalising circuit consists of a series combination of capacitor C and resistor RC across each thyristor. This resistance RC (along with parallel connected diode) |
| A. | limits charging current |
| B. | limits discharging current |
| C. | limits both charging and discharging currents |
| D. | none of the above |
| Answer» C. limits both charging and discharging currents | |
| 161. |
Thyristors are not suitable for logic circuits. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 162. |
The advantage of modified series inverter with two inductors and two capacitors is |
| A. | the intermittent operation of battery is avoided |
| B. | efficiency of circuit is more |
| C. | the output frequency is low |
| D. | all of the above |
| Answer» B. efficiency of circuit is more | |
| 163. |
A single phase semiconverter is feeding a highly inductive load and has freewheeling diode across the load. The waveshapes of output voltage and output current |
| A. | are similar |
| B. | are not similar |
| C. | may be similar or dissimilar |
| D. | are similar only if firing angle is zero |
| Answer» C. may be similar or dissimilar | |
| 164. |
A silicon controlled switch has : |
| A. | 2 leads |
| B. | 3 leads |
| C. | 4 leads |
| D. | 5 leads |
| Answer» D. 5 leads | |
| 165. |
In a power diode the reverse recovery time is the time from the instant the forward current is zero to the instant when reverse recovery current has decayed to |
| A. | 50% of peak reverse current |
| B. | 25% of peak reverse current |
| C. | 10% of peak reverse current |
| D. | zero value |
| Answer» B. 25% of peak reverse current | |
| 166. |
In a 3 phase fully controlled converter the firing frequency is |
| A. | 3 times the line frequency |
| B. | 6 times the line frequency |
| C. | 9 times the line frequency |
| D. | 12 times the line frequency |
| Answer» C. 9 times the line frequency | |
| 167. |
In a single phase full wave regulator, the rms current in each thyristors is Ir The run load current is equal to |
| A. | 2Ir |
| B. | √2 Ir |
| C. | Ir |
| D. | Ir / √2 |
| Answer» C. Ir | |
| 168. |
In a single phase full wave regulator feeding a resistive load, the average current over one full cycle |
| A. | is always zero |
| B. | cannot be zero |
| C. | may be sometimes zero |
| D. | is always positive |
| Answer» B. cannot be zero | |
| 169. |
In a 3 phase semiconverter, the dc output voltage for a certain firing angle is 50% of the maximum possible value. The firing angle is |
| A. | 30° |
| B. | 60° |
| C. | 90° |
| D. | 120° |
| Answer» D. 120° | |
| 170. |
In a single phase full wave ac regulator feeding R-L load, the gate pulses |
| A. | are always of short duration |
| B. | may be of short duration |
| C. | should be rectangular with width (π - α) |
| D. | cannot be rectangular with width (π - α) |
| Answer» D. cannot be rectangular with width (π - α) | |
| 171. |
Which chopper circuit uses saturable reactor? |
| A. | Auxiliary commutated |
| B. | Jones chopper |
| C. | Morgan chopper |
| D. | Load commutated |
| Answer» D. Load commutated | |
| 172. |
In a 3 phase full converter, the instantaneous output voltage can have 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° | |
| 173. |
A TRIAC can be turned on : |
| A. | by applying a positive signal to gate |
| B. | by applying a negative signal to gate |
| C. | by applying either positive or negative signal to gate |
| D. | none of the above |
| Answer» D. none of the above | |
| 174. |
Assertion (A): A dual converter may be circulating current type or non circulating current type.Reason (R): In circulating current dual converter only one converter can be operated at one 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» D. A is wrong but R is correct | |
| 175. |
It is possible to use a freewheeling diode in |
| A. | single phase half wave controlled rectifier as well as in single phase full wave controlled rectifier (M - 2 connection) |
| B. | single phase half wave controlled rectifier but not in single phase full wave controlled rectifier (M - 2 connection) |
| C. | single phase full wave controlled rectifier (M - 2 connection) but not in single phase half wave controlled rectifier |
| D. | all controlled rectifier circuits |
| Answer» E. | |
| 176. |
A cycloconverter can be |
| A. | step down |
| B. | step up |
| C. | step down or step up |
| D. | none of the above |
| Answer» D. none of the above | |
| 177. |
Assertion (A): Power transistor has lower switching time than SCR Reason (R): Power transistor has greater switching time than SCR |
| 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» E. | |
| 178. |
Assertion (A): A transistor requires a continuous base signal for conduction but a thyristor requires a gate pulse.Reason (R): Transistor find widespread application in power electronic circuits. |
| 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 | |
| 179. |
When a thyristor is conducting, the voltage drop across it |
| A. | is absolutely constant |
| B. | decreases with increase in load current |
| C. | increases slightly with increase in load current |
| D. | none of the above |
| Answer» D. none of the above | |
| 180. |
A chopper is a high efficiency circuit. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 181. |
In dielectric heating, the thyristor circuits consist of |
| A. | rectifier-chopper combination |
| B. | controlled rectifier |
| C. | ac regulator |
| D. | rectifier-inverter combination |
| Answer» E. | |
| 182. |
Assertion (A): A GTO circuit is more compact than SCR circuit 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» B. Both A and R correct but R is not correct explanation of A | |
| 183. |
A Shockley diode can be used |
| A. | in place of SCR |
| B. | as a trigger switch for SCR |
| C. | in place of UJT |
| D. | both in place of SCR and as a trigger switch for SCR |
| Answer» C. in place of UJT | |
| 184. |
An SCR is triggered at 40° in the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80°, the average anode current is likely to be |
| A. | 50 A |
| B. | 25 A |
| C. | less than 50 A but more than 25 A |
| D. | less than 25 A |
| Answer» D. less than 25 A | |
| 185. |
Assertion (A): An inverter does not require forced commutation Reason (R): A series inverter is a forced commutation inverter. |
| 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» E. | |
| 186. |
Assertion (A): A fully controlled bridge converter can operate in first and fourth quadrant.Reason (R): A semi converter is cheaper than a full converter. |
| 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 | |
| 187. |
A thyristor has a maximum allowable junction temperature of 120°C and the ambient temperature is 40°C. If thermal resistance is 1.6° C/W, the maximum allowable internal power dissipation is |
| A. | 20 W |
| B. | 50 W |
| C. | 92 W |
| D. | 128 W |
| Answer» C. 92 W | |
| 188. |
Assertion (A): An ideal rectifier should have unity harmonic factorReason (R): An ideal rectifier should have unity displacement factor. |
| 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» E. | |
| 189. |
A single phase half wave controlled rectifier circuit has a free wheeling diode. The load is a combination of R and L. The firing angle is α. The period of conduction of SCR and free wheeling diode respectively are |
| A. | α < ωt < π and π < ωt < (2π + α) |
| B. | α < ωt < π and π < ωt < 2π |
| C. | α < ωt < (π + α) and (π + α) < ωt < 2π |
| D. | α < ωt < π and π < ωt < (2π - α) |
| Answer» B. α < ωt < π and π < ωt < 2π | |
| 190. |
As the firing of a thyristor is delayed, the output voltage of a controlled rectifier decreases. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 191. |
All inverters use forced commutation. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 192. |
A voltage VBB is applied across the terminals of a UJT. The emitter voltage at peak point is |
| A. | hVBB |
| B. | (h + 1) VBB |
| C. | hVBB + VD |
| D. | VD |
| Answer» D. VD | |
| 193. |
The waveshape of output voltage of half bridge inverter is |
| A. | sinusoidal |
| B. | square |
| C. | triangular |
| D. | either (a) or (b) |
| Answer» C. triangular | |
| 194. |
In a certain inverter circuit each thyristor carries 26.67 A for 60°, 13.33 A for 120° and zero A for 180° of the cycle. The rms current of thyristor is |
| A. | 20 A |
| B. | 13.33 A |
| C. | 6.67 A |
| D. | 3.33 A |
| Answer» C. 6.67 A | |
| 195. |
A dc chopper V = 500 V feeds an electric fraction dc series motor. The chopping frequency is 400 Hz. The series inductance required to limit the maximum current swing to 10 A is |
| A. | 20 mH |
| B. | about 31 mH |
| C. | about 51 mH |
| D. | about 92 mH |
| Answer» C. about 51 mH | |
| 196. |
Inverters find applications in |
| A. | HVDC transmission |
| B. | UPS |
| C. | variable speed ac drives |
| D. | all of the above |
| Answer» E. | |
| 197. |
Assertion (A): SUS is a PUT and avalanche diode connected between gate and cathodeReason (R): SBS has two SUS inbuilt together and connected in anti-parallel |
| 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 | |
| 198. |
A single phase half bridge inverter required to feed R-L loads needs |
| A. | 2 thyristors |
| B. | 4 thyristors |
| C. | 2 thyristors and two diodes |
| D. | 4 thyristors and 4 diodes |
| Answer» D. 4 thyristors and 4 diodes | |
| 199. |
The terminals of a power BJT are called |
| A. | emitter, base, collector |
| B. | emitter, base, drain |
| C. | source, base, drain |
| D. | source, base, collector |
| Answer» B. emitter, base, drain | |
| 200. |
In a 3 phase semiconverter, the freewheeling diode comes into operation only if firing angle |
| A. | is zero |
| B. | is 60° |
| C. | is more than 60° |
| D. | is more than 90° |
| Answer» D. is more than 90° | |