MCQs on Power Electronics

1)   Unipolar modulation is generally used in a. AC - AC converters b. AC - DC converters c. DC - AC converters d. DC - DC converters Answer   ANSWER: DC - DC converters Explanation:  No explanation is available for this question!

2)   The power demand can be estimated approximately by a. Load survey method. b. Mathematical method. c. Statistical method. d. Economic parameters. Answer   ANSWER: Statistical method. Explanation:  No explanation is available for this question!

3)   What is the advantage of HRC fuses over Rewirable fuses? a. High speed operation b. High rupturing capacity c. No ageing effect. d. All of the above. Answer   ANSWER: All of the above. Explanation:  No explanation is available for this question!

4)   If a shunt motor is started with its field winding open then a. It will rotate at the same speed as that with its field winding closed b. It will rotate at less speed as that with its field winding closed c. It will rotate at dangerously high speed d. None of these Answer ANSWER: It will rotate at dangerously high speed

5)   Electrical power output in a d.c. generator is equal to a. Electrical power developed in armature – copper losses b. Mechanical power input – iron and friction losses c. Electrical power developed in armature – iron and copper losses d. Mechanical power input – iron and friction losses – copper losses Answer   ANSWER: Mechanical power input – iron and friction losses – copper losses

6)   The quadrant operation of BJT is represented by a. 1 b. 2 c. 3 d. 4 Answer   ANSWER: 2

7)   The switching function of semiconductor devices can be characterized with a. Duty ratio only b. Frequency only c. Duty ratio and frequency d. Duty ratio, frequency and time delay Answer   ANSWER: Duty ratio, frequency and time delay Explanation:  No explanation is available for this question!

8)   AC power in a load can be controlled by using a. two SCR’s in parallel opposition b. two SCR’s in series c. three SCR’s in series d. four SCR’s in series Answer   ANSWER: two SCR’s in parallel opposition Explanation:  No explanation is available for this question!

9)   An SCR is made up of silicon because a. silicon has large leakage current than germanium b. silicon has small leakage current than germanium c. silicon has small leakage voltage than germanium d. silicon has large leakage voltage than germanium Answer   ANSWER: silicon has small leakage current than germanium Explanation:  No explanation is available for this question!

10)   The output power of the cascaded amplifier / attenuator system can be determined using  a. Actual gain of amplifier b. Actual gain of amplifier and attenuator c. Gain in dB of amplifier and attenuator d. Actual gain of attenuator Answer   ANSWER: Actual gain of amplifier and attenuator Explanation:  No explanation is available for this question! 11)   LISN is a device used to measure conducted emissions. LISN stands for a. Line integrated stabilization network b. Line impedance stabilization network c. Line integrated stored network d. Laser integrated stabilization networking Answer   ANSWER: Line impedance stabilization network 12)   In current commutated DC-DC choppers, the voltage spike appears across the load when a. Voltage across the commutating inductances collapses b. The capacitance voltage adds to the supply voltage c. Both (a) and (b) d. None of these Answer   ANSWER: Both (a) and (b) 13)   In a load commutated DC - DC chopper, the capacitor has a a. Symmetric triangular voltage across itself b. Symmetric rectangular voltage across itself c. Symmetric trapezoidal voltage across itself d. Symmetric sinusoidal voltage across itself Answer   ANSWER: Symmetric trapezoidal voltage across itself 14)   Voltage commutation circuit can be converted into a current commutation by interchanging the positions of a. Diode and capacitor b. Capacitor and SCR c. Inductor and capacitor d. Capacitor and load Answer   ANSWER: Diode and capacitor 15)   For swept frequency measurements, the input impedance of the mismatched transmission line would vary with frequency as the electrical length of the transmission line would a. Decrease with frequency b. Remains same with change in frequency c. Increase with frequency d. Either (a) or (b) Answer   ANSWER: Increase with frequency 16)   In EMC signal, the source delivers maximum power to the input of transmission line when the transmission line input impedance a. Is equal to the source resistance b. Greater than the source resistance c. Smaller than the source resistance d. None of these Answer   ANSWER: Is equal to the source resistance 17)   In radiative coupling, the emitter radiation field a. Decays as 1 / R, where R is the separation distance between the emitter and the receptor b. Decays as R, where R is the separation distance between the emitter and the receptor c. Decays as 1 / 2 R, where R is the separation distance between the emitter and the receptor d. Decays as 2R, where R is the separation distance between the emitter and the receptor Answer   ANSWER: Decays as 1 / R, where R is the separation distance between the emitter and the receptor 18)   The effects of EMI can be reduced by  a. Suppressing emissions b. Reducing the efficiency of the coupling path c. Reducing the susceptibility of the receptor d. All of these Answer   ANSWER: All of these 19)   Between the incoming and outgoing devices in voltage commutation a. Large overlapping takes place b. Small overlapping operation c. No overlapping operation d. None of these Answer   ANSWER: No overlapping operation 20)   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   ANSWER: Dependent on both the load current and load voltage behind the short circuit current

21)   In a three phase converter, the number of notches per cycle is a. One b. Three c. Six d. Nine Answer   ANSWER: Six

22)   In a 3 phase CSI, if the required line output voltages are balanced and 120 degree out of phase, then the chopping angles are used to eliminate only the harmonics at frequencies a. 5 b. 7 c. 11 d. All of these Answer   ANSWER: All of these

23)   For similar carrier and modulating signals, the line current used in CSI is a. Identical to line voltage in a VSI b. Identical to line current in VSI c. Identical to phase voltage in VSI d. Identical to phase voltage in CSI Answer   ANSWER: Identical to line voltage in a VSI

24)   Under harmonic free load voltages, the 3 phase VSI  a. Does not contains second harmonic b. Does not contains third harmonic c. Does not contains fifth harmonic d. Does not contains seventh harmonic Answer   ANSWER: Does not contains second harmonic

25)   The square wave operation of 3 phase VSI lines contains the harmonics. The amplitudes are a. Directly proportional to their harmonic order b. Inversely proportional to their harmonic order c. Not related to their harmonic order d. None of these Answer   ANSWER: Inversely proportional to their harmonic order

26)   In bipolar modulation, the carrier is symmetric about zero with amplitude equal to Cm, the PWM output  a. Zero b. Switches between - 1 / 2 and + 1 / 2 c. Switches between - 1 and + 1 d. Switches between 0 and + 1 Answer   ANSWER: Switches between - 1 / 2 and + 1 / 2

27)   Double fourier series analysis of PWM is  a. Two dimensional functions b. Three dimensional functions c. One dimensional functions d. All of these Answer   ANSWER: Two dimensional functions

28)   In single phase VSI, the harmonic which is not present is a. 2nd b. 3rd c. 5th d. 7th Answer   ANSWER: 2nd

29)   Very large values of modulation index (greater than 3.24) lead to a. Square AC output voltage b. Sine AC output voltage c. Triangular AC output voltage d. Trapezoidal AC output voltage Answer   ANSWER: Square AC output voltage

30)   Single phase VSI are mainly used in  a. Power supplies b. Ups c. Multilevel configuration d. All of these Answer   ANSWER: All of these

31)   For bidirectional operation of converters a. A parallel combination of controllable switch and a diode is used b. A parallel combination of controllable switch and capacitor is used c. A series combination of controllable switch and a diode is used d. A series combination of controllable switch and a capacitor is used Answer   ANSWER: A parallel combination of controllable switch and a diode is used

32)   For a buck converter to reduce the conduction losses in diode a. A high on - resistance switch can be added in parallel b. A low on - resistance switch can be added in parallel c. A high on - resistance switch can be added in series d. A low on - resistance switch can be added in series Answer   ANSWER: A low on - resistance switch can be added in parallel

33)   The conduction losses in IGBT is a. More than that of MOSFET b. Lower than that of MOSFET c. Equal to that of MOSFET d. Equal to that of BJT Answer   ANSWER: Lower than that of MOSFET

34)   The power MOSFET device is a a. Current controlled unipolar device b. Voltage controlled unipolar device c. Current controlled bipolar device d. Voltage controlled bipolar device Answer   ANSWER: Voltage controlled unipolar device

35)   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   ANSWER: Harmonic distortion increases and quality of input current decreases

36)   The most suited gate pulses given to the AC regulator with R - L load can be in the form of a. Continuous signal b. Large isolating pulse transformer c. A train of pulses d. None of these Answer   ANSWER: A train of pulses

37)   Harmonics in 3 phase inverters can be reduced by using a. Passive filter b. Active filter c. Both passive and active filters d. None of these Answer   ANSWER: Both passive and active filters

38)   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   ANSWER: There is always a path for the dc current independent of the ac line

39)   The input current waveform of a bridge controlled rectifier when the load is perfectly filtered is a. Sine wave b. Square wave c. Saw - tooth wave d. Trapezoidal wave Answer   ANSWER: Square wave

40)   A full wave rectifier with resistive load produces a. Second harmonic b. Third harmonic c. Fifth harmonic d. Do not produce harmonics Answer   ANSWER: Do not produce harmonics 41)   A crowbar is a circuit which is used to protect a a. voltage sensitive load from excessive dc power supply output voltages b. current sensitive load from excessive dc power supply output voltages c. voltage sensitive load from excessive ac power supply output voltages d. current sensitive load from excessive ac power supply output voltages Answer   ANSWER: voltage sensitive load from excessive dc power supply output voltages 42)   An SCR can be used  a. as static conductor b. for power control c. for speed control of dc shunt motor d. all of these Answer   ANSWER: all of these 43)   TRIAC is a semiconductor power electronic device which contains  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   ANSWER: Two SCR’s connected in reverse parallel 44)   Silicon controlled rectifier can be turned on a. By applying a gate pulse and turned off only when current becomes zero b. And turned off by applying gate pulse c. By applying a gate pulse and turned off by removing the gate pulse d. By making current non zero and turned off by making current zero Answer   ANSWER: By applying a gate pulse and turned off only when current becomes zero 45)   In a square - wave operation of 3 phase CSIs, the power values are on for a. 60 degree b. 90 degree c. 120 degree d. 150 degree Answer   ANSWER: 120 degree 46)   A carrier based PWM technique in CSI is composed of a. A switching pulse generator and a shorting pulse generator b. A shorting pulse distributor c. A switching and shorting pulse combination d. All of these Answer   ANSWER: All of these 47)   In variable frequency, PWM gain  a. Phase lead helps to increase the phase margin of the control loop b. Phase lag helps to increase the phase margin of the control loop c. Phase lead helps to decrease the phase margin of the control loop d. Phase lag helps to decrease the phase margin of the control loop Answer   ANSWER: Phase lead helps to increase the phase margin of the control loop 48)   In constant frequency PWM, at perturbation the amplitude of the sinusoidal component is a  a. Linear function b. Non linear function c. Constant function d. None of these Answer   ANSWER: None of these 49)   The transfer function of PWM is generally developed in a. Time domain b. Frequency domain c. Either (a) or (b) d. None of these Answer   ANSWER: Either (a) or (b) 50)   In the SPWM, the modulating signal is  a. Square b. Sinusoidal c. Triangular d. Saw - tooth Answer   ANSWER: Sinusoidal

51)   In a full bridge VSI, in order to avoid the short circuit across the DC bus and the undefined AC output voltage condition, the modulating technique should ensure that a. Top switch of each leg is on at any instant b. Bottom switch of each leg is on at any instant c. Either (a) or (b) d. None of these Answer   ANSWER: Either (a) or (b)

52)   In a lossless inverter, the average power absorbed in one period by the load must be a. Equal to the average power supplied by the dc source b. Greater than the average power supplied by the dc source c. Lesser than the average power supplied by the dc source d. Equal to the average power supplied by the ac source Answer   ANSWER: Equal to the average power supplied by the dc source

53)   A step - down choppers can be used in a. Electric traction b. Electric vehicles c. Machine tools d. All of these Answer   ANSWER: All of these

54)   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   ANSWER: Either (a) or (b)

55)   The opposite of susceptibility is a. Immunity b. Emission c. Interference d. Electromagnetic compatibility Answer   ANSWER: Immunity

56)   The ability of an electronic system to function properly in its intended electromagnetic environment and should not be a source of pollution to that electromagnetic environment is known as a. Susceptibility b. Emission c. Interference d. Electromagnetic compatibility Answer   ANSWER: Electromagnetic compatibility

57)   If all the SCR’s of 3 phase PAC is replaced by diodes, they would be triggered a. 120 degree after the zero crossing of the corresponding line voltages b. 60 degree after the zero crossing of the corresponding line voltages c. 120 degree before the zero crossing of the corresponding line voltages d. 60 degree before the zero crossing of the corresponding line voltages Answer   ANSWER: 60 degree after the zero crossing of the corresponding line voltages

58)   For commutation in three phase PAC, normally balanced three phase voltages VR, VY and VB are connected to the three legs of the converter via a. Three inductances b. Three capacitances c. Three resistance d. Three transistors Answer   ANSWER: Three inductances

59)   In square wave operation mode of 3 phase VSI, the VSI a. Can control the load voltage b. Cannot control the load voltage c. Cannot control the load voltage except by means of dc link voltage d. Cannot control the load voltage except by means of dc link current Answer   ANSWER: Cannot control the load voltage except by means of dc link voltage

60)   In a 3 phase VSI SPWM to use a single carrier signal and preserve the features of PWM technique, the normalized carrier frequency should be a. Multiple of two b. Odd multiple of three c. Odd multiple of five d. Odd multiple of seven Answer   ANSWER: Odd multiple of three

61)   Regulator sampling PWM is usually used in a. High power inverters b. Rectifiers c. Low power inverters d. Only (a) and (b) Answer   ANSWER: Only (a) and (b)

62)   A combination of synchronized leading edge and trailing edge modulation has also been used to control a a. Boost single - phase power factor converter b. A buck dc - dc converter to reduce ripple in the intermediate dc bus capacitor c. Both (a) and (b) d. None f these Answer   ANSWER: Both (a) and (b)

63)   If energy is taken from the AC side of the inverter and sends it back into the DC side, then it is known as a. Motoring mode operation b. Braking mode operation c. Regenerative mode operation d. None of these Answer   ANSWER: Regenerative mode operation

64)   The ac output voltage waveform of VSI and AC output current waveform of CSI respectively is composed of a. High dv / dt, low di / dt b. Low dv / dt, low di / dt c. Low dv / dt, high di / dt d. High dv / dt, high di / dt Answer   ANSWER: High dv / dt, high di / dt

65)   Advantages of Cuk converter is / are a. Large number of reactive component b. Low stress on switch c. Low stress on capacitor d. None of these Answer   ANSWER: None of these

66)   In a flyback converter, the inductor of the buck-boost converter has been replaced by a a. Flyback capacitor b. Flyback resistor c. Flyback transformer d. Flyback transistor Answer   ANSWER: Flyback transformer

67)   In a push - pull converter, the filter capacitor can be obtained as a. Cmin = V / ( Vr L f2 ) b. Cmin= ( 1 – D ) V / ( Vr L f2 ) c. Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 ) d. Cmin= ( 1 – 2 D ) V / 42 ( Vr L f2 ) Answer   ANSWER: Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 )

68)   MOSFET stands for a. Metal - oxide semiconductor field effect transistor b. Molybdenum - oxide semiconductor field effect transistor c. Metal - oxide silicon field effect transistor d. Metal - oxide semiconductor field effect transmitter Answer  s ANSWER: Metal - oxide semiconductor field effect transistor

69)   A MOSFET, for its conduction uses a. Only minority carriers b. Only majority carriers c. Both minority and majority carriers d. None of these Answer   ANSWER: Only majority carriers

70)   An RC snubber network used in BJT a. Divert the collector current during turn - off b. Improves the reverse bias safe operating area c. Dissipates a fair amount of switching power d. All of these Answer   ANSWER: All of these

71)   The ac voltage controller can be used for  a. Lighting and heating control b. On - line transformer tap changing c. Soft starting d. All of these Answer   ANSWER: All of these

72)   The phase angle of gate signal in TRIAC can be shifted by using  a. A capacitor b. A variable resistor c. An inductor d. Only (a) and (b) Answer   ANSWER: Only (a) and (b)

73)   A TRIAC can be turned on with  a. Positive voltage at the gate terminal b. Negative voltage at the gate terminal c. Either (a) or (b) d. None of these Answer   ANSWER: Either (a) or (b)

74)   DIAC and TRIAC both are semiconductors devices and conduct in a. DIAC conducts in forward direction and TRIAC conducts in reverse direction b. Both conducts in forward direction c. Both conducts in reverse direction d. Both conducts in either direction Answer   ANSWER: Both conducts in either direction

75)   The Graetz bridge makes excellent use of  a. Current transformer b. Potential transformer c. Power transformer d. SCR Answer   ANSWER: Power transformer

76)   If the firing angle becomes negative, then the rectifier begins to work as a. A rectifier b. An inverter c. A chopper d. A regulator Answer   ANSWER: An inverter

77)   In a 3 phase half wave rectifier, when firing angle is less than 90 degree, then the average dc output voltage becomes a. Positive b. Negative c. Zero d. None of these Answer   ANSWER: Positive

78)   Transformer utilization factor is a measure of the merit of a rectifier circuit. It is the ratio of a. AC input power to the transformer volt - amp rating required by secondary b. AC input power to the transformer volt - amp rating required by primary c. DC output power to the transformer volt - amp rating required by secondary d. DC output power to the transformer volt - amp rating required by primary Answer   ANSWER: DC output power to the transformer volt - amp rating required by secondary

79)   Ripple factor is the ratio of a. Rms value of the ac component of load voltage to the dc voltage b. Average value of the ac component of load voltage to the peak value of voltage c. Average value of the dc component of load voltage to the ac voltage d. Peak value of the dc component of load voltage to the ac voltage Answer   ANSWER: Rms value of the ac component of load voltage to the dc voltage

80)   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   ANSWER: Root mean square value of voltage and current to its average value

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81)   The curve between V and I of SCR when anode is positive w.r.t cathode and when anode is negative w.r.t cathode are known as a. both as forward characteristics b. both as reverse characteristics c. former as forward characteristics and later as reverse characteristics d. former as reverse characteristics and later as forward characteristics Answer   ANSWER: former as forward characteristics and later as reverse characteristics

82)   With gate open, the maximum anode current at which SCR is turned off from ON condition is called a. breakdown voltage b. peak reverse voltage c. holding current d. latching current Answer   ANSWER: holding current

83)   Bidirectional semiconductor device is a. Diode b. BJT c. SCR d. TRIAC Answer   ANSWER: TRIAC

84)   An ideal diode is a. Unidirectional b. Bidirectional c. Fixed voltage polarity d. Only (a) and (c) Answer   ANSWER: Only (a) and (c)

85)   The IGBT resulted in higher switching speed and lower energy losses. It can be used for a. Uninterruptible power supplies b. Induction heating system c. Constant voltage and frequency power supplies d. All of these Answer   ANSWER: All of these

86)   To detect an over - current fault condition, the most reliable method is to connect 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   ANSWER: Current sensor in series with IGBT

87)   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   ANSWER: All of these

88)   The maximum firing angle in the half wave controlled regulator is a. 180 degree b. 190 degree c. 200 degree d. 210 degree Answer   ANSWER: 210 degree

89)   In a phase controlled 3 phase ac voltage controller, the harmonic present is a. 2nd b. 3rd c. 5th d. 7th Answer   ANSWER: 2nd

90)   In dual converters, a. Both rectifiers provides positive current to the load b. Both rectifiers provide negative current to the load c. One rectifiers provide positive current to the load and the other negative current d. One rectifier provide positive current to the source and the other negative current to the load Answer   ANSWER: Both rectifiers provides positive current to the load 91)   Advantages of HVDC transmission over AC system is / are a. Reversal of power can be controlled by firing angle b. Very good dynamic behavior c. They can link two AC system operating unsynchronized d. All of these Answer   ANSWER: All of these 92)   In rectifiers, load current flow is a. Unidirectional b. Bidirectional c. Either (a) or (b) d. Non directional Answer   ANSWER: Unidirectional 93)   Due to non sinusoidal waveform of the input current, the power factor of the rectifier is a. Negatively affected by firing angle b. Negatively affected by distortion of the input current c. Positively affected by both firing angle and distortion of the input current d. Both (a) and (b) Answer   ANSWER: Both (a) and (b) 94)   The man made noise sources is / are a. Motors b. Switches, radio interferences c. Computers, digital electronics d. All of these Answer   ANSWER: All of these 95)   Any electrical signal present in a circuit other than the desired signal is known as a. Noise b. Distortion c. Interference d. All of these Answer   ANSWER: Noise 96)   In commutation PAC stands for a. Permanent angle converter b. Phase angle converter c. Phase angle commutation d. Phase and commutation Answer   ANSWER: Phase angle converter 97)   In the operation and control of both naturally commutated and forced commutated SCR base converter, commutation plays an important role. The converters is / are a. AC - DC b. DC - DC c. DC - AC d. All of these Answer   ANSWER: All of these 98)   In a 3 phase VSI out of eight valid states, the number of valid states that produce zero ac line voltages is/are a. One b. two c. Three d. Four Answer   ANSWER: two 99)   In a three phase voltage source inverters a. Only amplitude of voltage is controllable b. Only phase is controllable c. Both amplitude and phase is controllable d. Amplitude, phase and frequency of voltages should always be controllable Answer   ANSWER: Amplitude, phase and frequency of voltages should always be controllable 100)   Double edge modulation eliminates certain harmonics when the reference is a a. Sine wave b. Square wave c. Triangular wave d. Trapezoidal wave Answer   ANSWER: Sine wave

101)   The carrier which are commonly used in constant - frequency PWM is a. Sawtooth carrier b. Inverted sawtooth carrier c. Triangle carrier d. All of these Answer   ANSWER: All of these

102)   A capacitive load in voltage source inverters generates  a. Small current spikes and can be reduced by using an inductive filter b. Large current spikes and can be increased by using an inductive filter c. Small current spikes and can be increased by using an inductive filter d. Large current spikes and can be reduced by using an inductive filter Answer   ANSWER: Large current spikes and can be reduced by using an inductive filter

103)   The main objective of static power converters is to a. Obtain an dc output waveform from a dc power supply b. Obtain an ac output waveform from a dc power supply c. Obtain an dc output waveform from a dc power supply d. Obtain an ac output waveform from a ac power supply Answer   ANSWER: Obtain an ac output waveform from a dc power supply

104)   The control method used for PWM dc - dc converter is a. Voltage mode control b. Current mode control c. Hysteric control d. All of these Answer   ANSWER: All of these

105)   The average value of the output voltage in a step - down dc chopper is given by a. V 0 = V s b. V 0 = D V s c. V 0 = V s / D d. V 0 = V s / ( 1 - D ) Answer   ANSWER: V 0 = D V s

106)   Choppers is a a. AC - DC converters b. AC - AC converters c. DC - AC converters d. DC - DC converters Answer   ANSWER: DC - DC converters

107)   In BJT, switching losses occurs a. Only at turn - on b. Only at turn - off c. Both at turn on and off d. None of these Answer   ANSWER: Both at turn on and off

108)   In BJT, the forward biased base emitter junction inject holes from base to emitter, 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) e. Only (b) and (c) Answer   ANSWER: Only (a) and (b)

109)   As the breakdown voltage reached, the DIAC exhibits a. Negative resistance characteristics b. Goes into avalanche condition c. Voltage drop snaps back d. All of these Answer   ANSWER: All of these

110)   DIAC are specifically designed to trigger a. TRIAC b. SCR c. GTO d. Only (a) and (b) Answer   ANSWER: Only (a) and (b)

111)   In a 3 phase bridge rectifier the ripple frequency is  a. Equal to the input frequency b. Twice the input frequency c. Three times the input frequency d. Six times the input frequency Answer   ANSWER: Six times the input frequency

112)   The sum of all phase current in a star connected primary winding with no neutral 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   ANSWER: Zero at all times

113)   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   ANSWER: Only (b) and (c)

114)   In a full wave rectifier, the rectification ratio is approximately equal to a. 61% b. 71% c. 81% d. 91% Answer   ANSWER: 81%

115)   In a single phase full wave rectifier, during blocking state the pea inverse voltage of diode is a. V m b. 2 V m c. V m / 2 d. 4 V m Answer   ANSWER: 2 V m

116)   A single phase ac - dc converter is also known as a. rectifier b. inverter c. chopper d. regulator Answer   ANSWER: rectifier

117)   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   ANSWER: anode current does not decrease at all

118)   Anode of an operational SCR is  a. Always positive w.r.t cathode b. Always negative w.r.t anode c. Always positive w.r.t anode d. Always negative w.r.t cathode Answer   ANSWER: Always positive w.r.t cathode

119)   In a silicon controlled rectifier, the load is connected a. Across anode b. In series with anode c. Across cathode d. In series with cathode Answer   ANSWER: In series with anode

120)   Number of PN junction in an SCR is a. Two b. Three c. Four d. Five Answer   ANSWER: Three

121)   IGBT stands for a. Insulated gate bipolar transistor b. Insulated gate bidirectional transistor c. Inductive gate bipolar transistor d. Inductive gate bidirectional transistor Answer   ANSWER: Insulated gate bipolar transistor

122)   An ideal switch is a. Lossless b. Carry current in any direction when it is on c. Does not carry any current in any direction when it is off d. All of these Answer   ANSWER: All of these

123)   In ac - dc conversion, when the switch is closed then the sum of voltages around 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   ANSWER: Non zero

124)   A rectifier with an external low pass filter is an example of a. Indirect switch matrix circuits b. Direct switch matrix circuits c. Embedded converters d. All of these Answer  ANSWER: Direct switch matrix circuits