McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering , Electronics and Communication Engineering .
| 151. |
A static induction thyristor |
| A. | is a majority carrier device |
| B. | is a minority carrier device |
| C. | either a majority carrier or minority carrier device |
| D. | has a total number of 2 leads |
| Answer» B. is a minority carrier device | |
| 152. |
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» B. one full wave of output | |
| 153. |
Which of these triggering methods for series connected SCRs use LASCR in the gate circuit? |
| A. | Resistance triggering |
| B. | Simultaneous triggering |
| C. | Sequential triggering |
| D. | Optical triggering |
| Answer» D. Optical triggering | |
| 154. |
A 3 phase ac regulator uses |
| A. | 3 thyristors |
| B. | 6 thyristors |
| C. | 9 thyristors |
| D. | 12 thyristors |
| Answer» B. 6 thyristors | |
| 155. |
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» A. firing angle | |
| 156. |
In a 3 phase full wave regulator feeding a star connected resistance load the input voltage is 400 V line to line. The firing angle is 160°. The line to line output voltage would be |
| A. | 400 V |
| B. | about 100 V |
| C. | about 20 V |
| D. | Zero |
| Answer» D. Zero | |
| 157. |
A thyristor is reverse biased. A positive gate pulse is applied. The thyristor |
| A. | will be turned on |
| B. | may or may not turn on |
| C. | will not turn on |
| D. | will turn on after sometime |
| Answer» C. will not turn on | |
| 158. |
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» A. high voltage output | |
| 159. |
A single phase half wave controlled rectifier circuit has an R-L load. A freewheeling diode is also in the circuit. When freewheeling diode is conducting the SCR |
| A. | is forward biased |
| B. | is reverse biased |
| C. | may be forward biased or reverse biased |
| D. | forward biased initially but reverse biased afterwards |
| Answer» B. is reverse biased | |
| 160. |
An SBS can conduct is one direction only. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 161. |
The number of doped regions in a SCR is |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 5 |
| Answer» C. 4 | |
| 162. |
All inverters use forced commutation. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 163. |
In 180° mode of operation of a 3 phase bridge inverter, two thyristors conduct at one time. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 164. |
A reactor is used in a dual converter operating in non-circulating current mode. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 165. |
Which of these commutation methods uses an auxiliary SCR? |
| A. | Class A |
| B. | Class B |
| C. | Class C |
| D. | Class D |
| Answer» C. Class C | |
| 166. |
A thyristor needs protection against |
| A. | high |
| B. | high |
| C. | both high and high |
| D. | either high or high |
| Answer» C. both high and high | |
| 167. |
In integral cycle control the period of on-off control should be more than mechanical time constant of load. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 168. |
A single phase half wave converter is feeding a resistive load. Just before triggering, the voltage across thyristor is |
| A. | Zero |
| B. | about 1 V |
| C. | same as input voltage |
| D. | twice the input voltage |
| Answer» C. same as input voltage | |
| 169. |
In a 3 phase full wave regulator feeding resistance load connected in star, the possible range of firing angle a is |
| A. | 0 ≤ ≤ 180° |
| B. | 0 ≤ ≤ 150° |
| C. | 0 ≤ ≤ 120° |
| D. | 0 ≤ ≤ 90° |
| Answer» B. 0 ≤ ≤ 150° | |
| 170. |
A 3 phase bridge inverter is fed by 400 V battery. The load is star connected and has a resistance of 10 Ω per phase. The peak value of load current is |
| A. | 40 A |
| B. | 20 A |
| C. | 10 A |
| D. | 5 A |
| Answer» B. 20 A | |
| 171. |
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» B. external circuit only | |
| 172. |
The rated current of a thyristor is 40 A. The holding current will be about : |
| A. | 20 A |
| B. | 1 A |
| C. | 100 mA |
| D. | 10 mA |
| Answer» D. 10 mA | |
| 173. |
The number of leads in a power semiconductor diode are |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 2 or 3 |
| Answer» A. 2 | |
| 174. |
If ton and toff are the turn on and turn off times of a thyristor, then |
| A. | ton and toff are almost equal |
| B. | ton >> toff |
| C. | toff >> ton |
| D. | ton is about twice toff |
| Answer» C. toff >> ton | |
| 175. |
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» A. firing an SCR | |
| 176. |
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. | 152 A |
| C. | 15 A |
| D. | none |
| Answer» C. 15 A | |
| 177. |
During forward blocking state of SCR, the voltage and current respectively are |
| A. | high and high |
| B. | low and low |
| C. | high and low |
| D. | low and high |
| Answer» C. high and low | |
| 178. |
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» C. 50 A | |
| 179. |
The two modes of operation of three phase bridge inverters are known as |
| A. | 60° mode and 120° mode |
| B. | 90° mode and 120° mode |
| C. | 120° mode and 180° mode |
| D. | 120° mode and 240° mode |
| Answer» C. 120° mode and 180° mode | |
| 180. |
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» B. 6 times the line frequency | |
| 181. |
Two thyristor of same rating and same specifications |
| A. | will have equal turn on and turn off periods |
| B. | will have equal turn on but unequal turn off periods |
| C. | may have equal or unequal turn on and turn off periods |
| D. | will have unequal turn on and turn off periods |
| Answer» C. may have equal or unequal turn on and turn off periods | |
| 182. |
The amount of dielectric heating is inversely proportional to frequency. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 183. |
A semiconverter feeding an RLE load operates in |
| A. | first quadrant only |
| B. | first and second quadrants |
| C. | first and fourth quadrants |
| D. | first and third quadrants |
| Answer» A. first quadrant only | |
| 184. |
The phenomenon of overlap in converter operation due to |
| A. | source resistance |
| B. | source inductance |
| C. | both source resistance and source inductance |
| D. | high value of firing angle |
| Answer» B. source inductance | |
| 185. |
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» C. less than 50 A but more than 25 A | |
| 186. |
In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally |
| A. | Equal |
| B. | Different |
| C. | equal or different |
| D. | different but sometimes equal |
| Answer» A. Equal | |
| 187. |
Current derating may be necessary when thyristors are operating in |
| A. | Series |
| B. | Parallel |
| C. | series or parallel |
| D. | none of the above |
| Answer» B. Parallel | |
| 188. |
A 3 kV circuit uses SCR of 800 V rating. If derating is 25%, the number of SCRs in series is |
| A. | 4 |
| B. | 5 |
| C. | 6 |
| D. | 8 |
| Answer» B. 5 | |
| 189. |
The terminals of a power MOSFET are called |
| A. | emitter, base, collector |
| B. | source, gate, drain |
| C. | source, base, drain |
| D. | emitter, gate, drain |
| Answer» B. source, gate, drain | |
| 190. |
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» C. anode current will remain constant | |
| 191. |
Thyristors are not suitable for logic circuits. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 192. |
The number of leads in an SCR are : |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 5 |
| Answer» B. 3 | |
| 193. |
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» C. more than 6 μs | |
| 194. |
The total number of leads in reverse conducting thyristor is |
| A. | 2 |
| B. | 3 |
| C. | 1 |
| D. | 4 |
| Answer» B. 3 | |
| 195. |
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» A. Both A and R are correct and R is correct explanation of A | |
| 196. |
A semi converter operates in two quadrants. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 197. |
A single phase half wave rectifier is feeding a resistive load. When a = 0, dc output voltage is 127 V. When a = 30°, the dc output voltage will be about |
| A. | 127 V |
| B. | 120 V |
| C. | 110 V |
| D. | 100 V |
| Answer» B. 120 V | |
| 198. |
A single phase full wave regulator feeds R-L load. The best gating signal is |
| A. | short duration pulses |
| B. | long duration pulses |
| C. | pulse train |
| D. | either (a) or (b) |
| Answer» C. pulse train | |
| 199. |
A 3 phase induction motor is fed by a 3 phase ac regulator to change the stator voltage. The variation in speed will be more if |
| A. | load torque is constant |
| B. | load torque increases with increase in speed |
| C. | load torque decreases with increase in speed |
| D. | either (a) or (b) |
| Answer» B. load torque increases with increase in speed | |
| 200. |
The waveshape of output voltage of half bridge inverter is |
| A. | sinusoidal |
| B. | square |
| C. | triangular |
| D. | either (a) or (b) |
| Answer» B. square | |
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