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MCQOPTIONS
This section includes 554 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics & Communication Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 101. |
The two modes of operation of three phase bridge inverters areknown 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» D. 120° mode and 240° mode | |
| 102. |
In ac - dc conversion, when the switch is closed then the sum of voltagesaround the loop is |
| A. | Zero |
| B. | Non zero |
| C. | Equal to the sum of voltage when switch is open |
| D. | Twice of the voltage when switch is open |
| Answer» C. Equal to the sum of voltage when switch is open | |
| 103. |
For dynamic equalizing circuit used for series connected SCRs, thechoice of C is based on: |
| A. | Reverse recovery characteristics |
| B. | Turn-on characteristics |
| C. | Turn-off characteristics |
| D. | Rise time characteristics |
| Answer» B. Turn-on characteristics | |
| 104. |
A resistor connected across the gate and cathode of an SCR in acircuit increases its |
| A. | dv/dt rating |
| B. | Holding current |
| C. | Noise Immunity |
| D. | Turn-off time |
| Answer» D. Turn-off time | |
| 105. |
Find the expression for output voltage for a step-up chopper, assume linearvariation of load current and α as the duty cycle. |
| A. | Vs |
| B. | Vs/α |
| C. | Vs/(1-α) |
| D. | Vs/√2 |
| Answer» D. Vs/√2 | |
| 106. |
A step - down choppers can be used in |
| A. | Electric traction |
| B. | Electric vehicles |
| C. | Machine tools |
| D. | All of these |
| Answer» E. | |
| 107. |
Find the output voltage for a step-up chopper when it is operated at a dutycycle of 50 % and Vs = 240 V. |
| A. | 240 V |
| B. | 480 V |
| C. | 560 V |
| D. | 120 V |
| Answer» C. 560 V | |
| 108. |
A four quadrant operation require: |
| A. | Two full converters in series |
| B. | Two full converters connected back to back |
| C. | Two full converters connected in parallel |
| D. | Two semi conductors connected back to back |
| Answer» C. Two full converters connected in parallel | |
| 109. |
When thyristors are connected in series and parallel, it may benecessary to have : |
| A. | current derating |
| B. | voltage derating |
| C. | both current and voltage derating |
| D. | none of the above |
| Answer» D. none of the above | |
| 110. |
For mercury arc rectifiers, the anode is usually made of |
| A. | Aluminium |
| B. | Copper |
| C. | Tungsten |
| D. | Graphite. |
| Answer» E. | |
| 111. |
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» C. 10 A | |
| 112. |
A thyristor can be termed as: |
| A. | DC switch |
| B. | AC switch |
| C. | both AC and DC switch |
| D. | none of the above |
| Answer» B. AC switch | |
| 113. |
In mercury arc rectifier, voltage drop at anode is due to |
| A. | energy spent in overcoming the electrostatic field |
| B. | high temperature inside the rectifier |
| C. | self-restoring property of mercury |
| D. | high ionization potential. |
| Answer» B. high temperature inside the rectifier | |
| 114. |
The values of duty cycle (α) lies between |
| A. | 0<α<1 |
| B. | 0>α>-1 |
| C. | 0<=α<=1 |
| D. | 1<α<100 |
| Answer» D. 1<α<100 | |
| 115. |
The output current in PWM DC - DC converters is equal to |
| A. | Average value of the output inductor current |
| B. | Product of an average inductor current and a function of duty ratio |
| C. | Either (a) or (b) |
| D. | None of these |
| Answer» D. None of these | |
| 116. |
DIAC are specifically designed to trigger |
| A. | TRIAC |
| B. | SCR |
| C. | GTO |
| D. | Only (a) and (b) |
| Answer» E. | |
| 117. |
For power output higher than 15 kW, the suitable rectifier is |
| A. | Single phase |
| B. | 3 phase |
| C. | Poly phase |
| D. | Only (b) and (c) |
| Answer» E. | |
| 118. |
The IGBT resulted in higher switching speed and lower energy losses. It canbe used for |
| A. | Uninterruptible power supplies |
| B. | Induction heating system |
| C. | Constant voltage and frequency power supplies |
| D. | All of these |
| Answer» D. All of these | |
| 119. |
The voltage will be |
| A. | 230 V |
| B. | 250 V |
| C. | 275 V |
| D. | 325 V |
| Answer» E. | |
| 120. |
In an arc rectifier the drop in voltage at the cathode is approximately |
| A. | 1 volt |
| B. | 6 to 7 volts |
| C. | 60 to 70 volts |
| D. | 1.2 V7 volts. |
| Answer» C. 60 to 70 volts | |
| 121. |
The on - state voltage drop of IGBT consists of |
| A. | Drop across the collector junction |
| B. | Drop across the drift region |
| C. | Drop across MOSFET portion |
| D. | All of these |
| Answer» E. | |
| 122. |
TRIAC is a semiconductor power electronic device whichcontains |
| A. | Two SCR’s connected in reverse parallel |
| B. | Two SCR’s connected in parallel |
| C. | Two SCR’s connected in series |
| D. | Two BJT’s connected in series |
| Answer» B. Two SCR’s connected in parallel | |
| 123. |
A GTO can be represented by two transistors T1 & T2. The current gain ofboth transistors are α1 and α2 respectively. A low value of gate current requires |
| A. | low value of α1 and α2 |
| B. | low value of α1 and high value of α2 |
| C. | high value of α1 and low value of α2 |
| D. | high values of α1 and α2 |
| Answer» C. high value of α1 and low value of α2 | |
| 124. |
An UJT exhibits negative resistance region: |
| A. | Before the break point |
| B. | Between peak and valley point |
| C. | After the valley point |
| D. | Both (a) and (c) |
| Answer» C. After the valley point | |
| 125. |
If T is the time period for a chopper circuit and α is its duty cycle, then thechopping frequency is |
| A. | Ton/α |
| B. | Toff/α |
| C. | α/Toff |
| D. | α/Ton |
| Answer» E. | |
| 126. |
The advantage of using free – wheeling diode in half controlled bridge converter is that |
| A. | There is always a path for the dc current independent of the ac line |
| B. | There is always a path for the ac current independent of the ac line |
| C. | There is always a path for the dc current dependent of the ac line |
| D. | There is always a path for the ac current independent of the ac line |
| Answer» B. There is always a path for the ac current independent of the ac line | |
| 127. |
Cuk-converter is better than Buck converter in terms of the output voltage. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 128. |
The input current waveform of a bridge controlled rectifier when the load isperfectly filtered is |
| A. | Sine wave |
| B. | Square wave |
| C. | Saw - tooth wave |
| D. | Trapezoidal wave |
| Answer» C. Saw - tooth wave | |
| 129. |
With increase in firing angle, |
| A. | Both harmonic distortion and quality of input current increases |
| B. | Harmonic distortion increases and quality of input current decreases |
| C. | Harmonic distortion decreases and quality of input current increases |
| D. | Both harmonic distortion and quality of input current decreases |
| Answer» C. Harmonic distortion decreases and quality of input current increases | |
| 130. |
The sum of all phase current in a star connected primary winding with noneutral connection is equal to |
| A. | Phase current |
| B. | Three times the phase current |
| C. | Three times the line current |
| D. | Zero at all times |
| Answer» E. | |
| 131. |
In a full wave rectifier, the rectification ratio is approximately equal to |
| A. | 61% |
| B. | 71% |
| C. | 81% |
| D. | 91% |
| Answer» D. 91% | |
| 132. |
In a single phase full wave regulator feeding a resistive load, theaverage 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 | |
| 133. |
During the commutation period in 3 phase converter, overlap time is |
| A. | Dependent on the load current |
| B. | Dependent on the voltage |
| C. | Dependent on both the load current and load voltage behind the short circuit current |
| D. | Independent on both the load current and load voltage |
| Answer» D. Independent on both the load current and load voltage | |
| 134. |
The principle of three phase cycloconverter is to |
| A. | add and remove number of SCRs |
| B. | vary progressively the firing angle of the devices |
| C. | keep the firing angle as 0° for all the devices |
| D. | none of the mentioned |
| Answer» C. keep the firing angle as 0° for all the devices | |
| 135. |
Once SCR starts conducting a forward current, its gate lossescontrol over: |
| A. | anode circuit voltage only |
| B. | anode circuit current only |
| C. | anode circuit voltage and current |
| D. | none of the above |
| Answer» D. none of the above | |
| 136. |
If the gate voltage of an SCR is removed, then the |
| A. | anode current decreases |
| B. | anode current does not decrease at all |
| C. | anode current increases |
| D. | cathode current increases |
| Answer» C. anode current increases | |
| 137. |
A single phase ac - dc converter is also known as |
| A. | rectifier |
| B. | inverter |
| C. | chopper |
| D. | regulator |
| Answer» B. inverter | |
| 138. |
In BJT, the forward biased base emitter junction inject holes from base toemitter, the holes |
| A. | Do not contribute to the collector current |
| B. | Result in net current flow component into the base |
| C. | Contribute to the collector current |
| D. | Only (a) and (b) |
| Answer» E. | |
| 139. |
To detect an over - current fault condition, the most reliable method is toconnect a |
| A. | Current sensor across IGBT |
| B. | Voltage sensor across IGBT |
| C. | Current sensor in series with IGBT |
| D. | Voltage sensor in series with IGBT |
| Answer» E. | |
| 140. |
Form factor of a rectifier is the ratio of |
| A. | Root mean square value of voltage and current to its peak value |
| B. | Root mean square value of voltage and current to its average value |
| C. | Average value of current and voltage to its root mean square value |
| D. | Peak value of current and voltage to its root mean square value |
| Answer» D. Peak value of current and voltage to its root mean square value | |
| 141. |
A single phase voltage controller has input of 230 V and a load of 15 Ω resistive. For 6 cycles on and 4 cycles off, determine the average value of SCR current. |
| A. | 21.68 A |
| B. | 200 mA |
| C. | 4.14 A |
| D. | 2.07 A |
| Answer» D. 2.07 A | |
| 142. |
The rated current of a thyristor is 40 A. The holding current willbe about : |
| A. | 20 A |
| B. | 1 A |
| C. | 100 mA |
| D. | 10 mA |
| Answer» E. | |
| 143. |
In a circulating-current type of dual converter, the nature of thevoltage across the reactor is: |
| A. | Alternating |
| B. | Pulsating |
| C. | Direct |
| D. | Triangular |
| Answer» B. Pulsating | |
| 144. |
During forward blocking state of SCR, the voltage and currentrespectively are |
| A. | high and high |
| B. | low and low |
| C. | high and low |
| D. | low and high |
| Answer» D. low and high | |
| 145. |
A single-phase full bridge inverter can operate in load-commutation mode in case load consists of: |
| A. | RL load |
| B. | RLC underdamped |
| C. | RLC damped |
| D. | RLC critically damped |
| Answer» C. RLC damped | |
| 146. |
The advantage of using free - wheeling diode in half controlled bridgeconverter is that |
| A. | There is always a path for the dc current independent of the ac line |
| B. | There is always a path for the ac current independent of the ac line |
| C. | There is always a path for the dc current dependent of the ac line |
| D. | There is always a path for the ac current independent of the ac line |
| Answer» B. There is always a path for the ac current independent of the ac line | |
| 147. |
Latching current for the GTOs is ________ as compared to CTs(Conventional thyristors). |
| A. | more |
| B. | less |
| C. | constant |
| D. | cannot be said |
| Answer» B. less | |
| 148. |
The maximum firing angle in the half wave controlled regulator is |
| A. | 180 degree |
| B. | 190 degree |
| C. | 200 degree |
| D. | 210 degree |
| Answer» B. 190 degree | |
| 149. |
The average life of the glass bulb rectifier is |
| A. | 100 to 150 hours |
| B. | 1000 to 1500 hours |
| C. | 10,000 to 15,000 hours |
| D. | 100,000 to 150,000 hours. |
| Answer» D. 100,000 to 150,000 hours. | |
| 150. |
In a phase controlled 3 phase ac voltage controller, the harmonic present is |
| A. | 2 |
| B. | 3 |
| C. | 5 |
| D. | 7 |
| Answer» C. 5 | |