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RRB MCQs

Practice RRB-oriented Electronics & Telecommunication Engineering MCQs with answers and explanations for technical exam preparation. Questions are arranged in pages of up to 100.

Question 1101
Power ElectronicsSCR

SCR stands for?

  • ASilicon Controlled Rectifier
  • BSeries Current Regulator
  • CSwitching Capacitor Rectifier
  • DSilicon Current Resistor
Report an error
Correct Answer: A. Silicon Controlled Rectifier
Explanation: SCR is the standard abbreviation for Silicon Controlled Rectifier, a thyristor device.
Reference: Standard power electronics: scr
Question 1103
Power ElectronicsSCR

The three terminals of an SCR are?

  • AAnode, cathode and gate
  • BCollector, base and emitter
  • CDrain, source and gate
  • DAnode, base and drain
Report an error
Correct Answer: A. Anode, cathode and gate
Explanation: The terminals of an SCR are anode (A), cathode (K) and gate (G).
Reference: Standard power electronics: scr
Question 1104
Power ElectronicsSCR

For normal forward turn-on of an SCR by gate triggering, the anode should be?

  • APositive with respect to cathode
  • BNegative with respect to cathode
  • CAt exactly zero potential in every case
  • DDisconnected from the supply
Report an error
Correct Answer: A. Positive with respect to cathode
Explanation: For forward blocking and gate-triggered turn-on, the anode is positive relative to the cathode.
Reference: Standard power electronics: scr
Question 1105
Power ElectronicsSCR

Once a conventional SCR has latched ON, removal of the gate signal normally?

  • ADoes not turn it OFF
  • BImmediately turns it OFF
  • CReverses its anode current
  • DMakes its holding current infinite
Report an error
Correct Answer: A. Does not turn it OFF
Explanation: After latching, the gate loses control over turn-off; anode current must be reduced below the holding current or reverse voltage applied.
Reference: Standard power electronics: scr
Question 1107
Power ElectronicsSCR

The minimum anode current needed immediately after triggering so that an SCR remains ON when the gate pulse is removed is called?

  • ALatching current
  • BReverse leakage current
  • CDisplacement current
  • DLoad current rating
Report an error
Correct Answer: A. Latching current
Explanation: Latching current is the minimum anode current required to establish regenerative conduction after the triggering signal is removed.
Reference: Standard power electronics: scr
Question 1108
Power ElectronicsSCR

For an SCR, the latching current is generally?

  • AGreater than the holding current
  • BLess than the holding current in every device
  • CExactly zero
  • DAlways equal to gate current
Report an error
Correct Answer: A. Greater than the holding current
Explanation: Typically the latching current is higher than the holding current because stronger current is required just after turn-on to establish conduction.
Reference: Standard power electronics: scr
Question 1109
Power ElectronicsTRIAC

A TRIAC can conduct main current in?

  • ABoth directions
  • BForward direction only
  • CReverse direction only
  • DNeither direction
Report an error
Correct Answer: A. Both directions
Explanation: A TRIAC is a bidirectional thyristor used for AC power control.
Reference: Standard power electronics: triac
Question 1110
Power ElectronicsDIAC & TRIAC

A DIAC is commonly used to?

  • AProvide bidirectional triggering for a TRIAC
  • BRectify high-power three-phase DC
  • CAct as a controlled DC motor
  • DStore magnetic energy
Report an error
Correct Answer: A. Provide bidirectional triggering for a TRIAC
Explanation: A DIAC has bidirectional breakover behavior and is commonly used to produce symmetrical TRIAC gate triggering.
Reference: Standard power electronics: diac & triac
Question 1112
Power ElectronicsPower MOSFET

Compared with an SCR, a power MOSFET can normally be turned OFF by?

  • ARemoving or appropriately changing its gate-to-source drive
  • BReducing load current below holding current only
  • CApplying a DIAC pulse only
  • DWaiting for AC current zero in every application
Report an error
Correct Answer: A. Removing or appropriately changing its gate-to-source drive
Explanation: A MOSFET is a fully controlled switch: its channel can be turned on and off by controlling gate voltage.
Reference: Standard power electronics: power mosfet
Question 1113
Power ElectronicsRectifiers

A rectifier converts electrical power from?

  • AAC to DC
  • BDC to AC
  • CDC to DC only
  • DAC to AC only
Report an error
Correct Answer: A. AC to DC
Explanation: A rectifier converts alternating input power into a unidirectional/DC output.
Reference: Standard power electronics: rectifiers
Question 1114
Power ElectronicsInverters

An inverter converts electrical power from?

  • ADC to AC
  • BAC to DC
  • CAC to AC only
  • DMechanical to electrical
Report an error
Correct Answer: A. DC to AC
Explanation: An inverter synthesizes an AC output from a DC source.
Reference: Standard power electronics: inverters
Question 1115
Power ElectronicsDC Choppers

A DC chopper is principally a?

  • ADC-to-DC converter
  • BAC-to-DC converter
  • CDC-to-AC converter
  • DAC-to-AC transformer only
Report an error
Correct Answer: A. DC-to-DC converter
Explanation: A chopper controls the average DC output obtained from a DC input through high-frequency switching.
Reference: Standard power electronics: dc choppers
Question 1116
Power ElectronicsAC Voltage Controllers

An AC voltage controller converts?

  • AFixed-frequency AC to variable-magnitude AC at the same basic frequency
  • BDC to AC
  • CAC directly to pure DC only
  • DDC to DC
Report an error
Correct Answer: A. Fixed-frequency AC to variable-magnitude AC at the same basic frequency
Explanation: An AC voltage controller regulates the RMS AC output, commonly by phase or integral-cycle control, while retaining the supply's fundamental frequency.
Reference: Standard power electronics: ac voltage controllers
Question 1117
Power ElectronicsCycloconverters

A cycloconverter directly converts?

  • AAC at one frequency to AC at another frequency
  • BDC to AC only
  • CAC to DC only
  • DDC to DC only
Report an error
Correct Answer: A. AC at one frequency to AC at another frequency
Explanation: A cycloconverter performs direct AC-to-AC frequency conversion without an intermediate DC link.
Reference: Standard power electronics: cycloconverters
Question 1118
Power ElectronicsFreewheeling Diode

A freewheeling diode connected across an inductive DC load mainly provides?

  • AA path for load current when the main switch or rectifier device stops supplying it
  • BA permanent short circuit across the source
  • CGate current for an SCR
  • DVoltage amplification
Report an error
Correct Answer: A. A path for load current when the main switch or rectifier device stops supplying it
Explanation: Inductive current cannot change instantaneously, so the freewheeling diode provides a path for continuing current and helps limit load voltage excursions.
Reference: Standard power electronics: freewheeling diode
Question 1119
Power ElectronicsControlled Rectifiers

In phase-controlled rectifiers, firing angle alpha is measured from?

  • AThe reference point where the device would naturally become forward-biased in the supply cycle
  • BThe instant of maximum load current only
  • CThe end of every negative half-cycle only
  • DThe gate-current peak regardless of supply waveform
Report an error
Correct Answer: A. The reference point where the device would naturally become forward-biased in the supply cycle
Explanation: The firing delay angle alpha specifies how long triggering is delayed from the natural forward-bias reference in each applicable cycle.
Reference: Standard power electronics: controlled rectifiers
Question 1120
Power ElectronicsControlled Rectifiers

For a single-phase half-wave controlled rectifier with a purely resistive load, increasing firing angle from 0 toward 180 degrees generally causes the average output voltage to?

  • ADecrease
  • BIncrease
  • CRemain constant
  • DBecome independent of the supply
Report an error
Correct Answer: A. Decrease
Explanation: Delaying SCR turn-on shortens the conduction interval, reducing the average output voltage for a resistive load.
Reference: Standard power electronics: controlled rectifiers
Question 1121
Power ElectronicsPower Diode

A power diode is primarily an?

  • AUncontrolled unidirectional power semiconductor device
  • BFully gate-controlled bidirectional device
  • CVoltage-controlled transistor only
  • DMechanical relay
Report an error
Correct Answer: A. Uncontrolled unidirectional power semiconductor device
Explanation: A diode's conduction is determined by circuit voltage/current conditions; it has no control terminal.
Reference: Standard power electronics: power diode
Question 1122
Power ElectronicsPower MOSFET

A power MOSFET is primarily a?

  • AVoltage-controlled device
  • BCurrent-controlled device requiring continuous base current
  • CFour-layer latching thyristor
  • DBidirectional breakover diode
Report an error
Correct Answer: A. Voltage-controlled device
Explanation: The insulated gate of a MOSFET is controlled mainly by gate-to-source voltage, with negligible steady-state gate current ideally.
Reference: Standard power electronics: power mosfet
Question 1123
Power ElectronicsSCR Protection

A small series inductor is often used with an SCR to limit excessive?

  • Adi/dt during turn-on
  • Bdv/dt in the OFF state only
  • CHolding current
  • DGate voltage ripple only
Report an error
Correct Answer: A. di/dt during turn-on
Explanation: An inductor opposes rapid current change and can keep SCR turn-on di/dt within its safe rating.
Reference: Standard power electronics: scr protection
Question 1124
Power ElectronicsSCR Commutation

SCR commutation means the process of?

  • ATurning the SCR OFF
  • BTurning the SCR ON by gate current
  • CIncreasing its breakover voltage
  • DMeasuring its gate resistance
Report an error
Correct Answer: A. Turning the SCR OFF
Explanation: Commutation reduces SCR current below the holding level and provides sufficient recovery conditions for the device to regain blocking capability.
Reference: Standard power electronics: scr commutation
Question 1125
Power ElectronicsSCR Commutation

In a line-commutated AC rectifier, an SCR can turn OFF naturally when?

  • AIts current falls to zero and reverse voltage is available
  • BIts gate pulse is removed while current remains high
  • CIts gate is made more positive
  • DThe supply frequency becomes zero
Report an error
Correct Answer: A. Its current falls to zero and reverse voltage is available
Explanation: Natural commutation uses the AC source to bring current to zero and reverse-bias the outgoing SCR.
Reference: Standard power electronics: scr commutation
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Question 1126
Power ElectronicsSCR Commutation

Forced commutation is especially required for a conventional SCR in many?

  • ADC circuits
  • BPurely line-commutated AC circuits only
  • CPassive resistor networks with no source
  • DUncontrolled diode rectifiers
Report an error
Correct Answer: A. DC circuits
Explanation: A DC source has no natural current zero, so auxiliary circuitry is often required to force SCR current below holding current.
Reference: Standard power electronics: scr commutation
Question 1127
Power ElectronicsSingle-Phase Controlled Rectifiers

For a single-phase half-wave controlled rectifier with a resistive load, the SCR conducts from firing angle alpha to?

  • Api radians
  • B2pi radians in every case
  • Calpha/2
  • Dpi/2 regardless of alpha
Report an error
Correct Answer: A. pi radians
Explanation: With a resistive load, current follows voltage and becomes zero at the supply zero crossing at omega t=pi.
Reference: Standard power electronics: single-phase controlled rectifiers
Question 1128
Power ElectronicsRectifier Numericals

For a single-phase half-wave controlled rectifier with resistive load and supply peak Vm, the average output voltage is?

  • AVm(1+cos alpha)/(2pi)
  • B2Vm cos alpha/pi
  • CVm sin alpha/pi
  • DVm(1-cos alpha)/pi
Report an error
Correct Answer: A. Vm(1+cos alpha)/(2pi)
Explanation: Averaging Vm sin(theta) from alpha to pi over a full 2pi period gives Vdc=Vm(1+cos alpha)/(2pi).
Reference: Standard power electronics: rectifier numericals
Question 1130
Power ElectronicsSCR Characteristics

In the forward-blocking region of an SCR, the device is forward biased but remains OFF until?

  • AIt is triggered or forward breakover is reached
  • BThe anode becomes negative
  • CThe load current becomes zero only
  • DThe cathode is disconnected
Report an error
Correct Answer: A. It is triggered or forward breakover is reached
Explanation: In forward blocking, an SCR supports positive anode-to-cathode voltage until gate triggering or breakover initiates regenerative turn-on.
Reference: Standard power electronics: scr characteristics
Question 1134
Power ElectronicsSCR Protection

A high rate of rise of forward voltage across an OFF SCR may cause unwanted turn-on due to?

  • AJunction capacitance current
  • BHolding current becoming zero
  • CLoad resistance becoming infinite
  • DGate resistance alone
Report an error
Correct Answer: A. Junction capacitance current
Explanation: Internal junction capacitances carry i=C dv/dt; excessive dv/dt can create sufficient internal current to trigger the SCR.
Reference: Standard power electronics: scr protection
Question 1135
Power ElectronicsSCR Protection

A snubber circuit connected across an SCR is commonly used to limit?

  • Adv/dt
  • BLoad frequency to zero
  • CGate current to exactly zero
  • DDC output power
Report an error
Correct Answer: A. dv/dt
Explanation: An RC snubber reduces the rate of rise of voltage across the SCR and helps prevent false triggering.
Reference: Standard power electronics: scr protection
Question 1136
Power ElectronicsFreewheeling Operation

One important benefit of a freewheeling diode in an inductive rectifier load is reduction of?

  • ANegative load-voltage excursions
  • BAverage load current to zero
  • CLoad inductance
  • DSupply frequency
Report an error
Correct Answer: A. Negative load-voltage excursions
Explanation: The diode provides a local current path and clamps the load voltage near zero during freewheeling, preventing substantial negative load voltage.
Reference: Standard power electronics: freewheeling operation
Question 1138
Power ElectronicsControlled Rectifiers

In a controlled rectifier, delaying the firing angle generally provides control over the?

  • AAverage output voltage
  • BSupply frequency
  • CNumber of semiconductor layers
  • DPhysical transformer turns ratio
Report an error
Correct Answer: A. Average output voltage
Explanation: Phase control changes the portion and polarity-weighted interval of the AC waveform applied to the load, thereby controlling average output voltage.
Reference: Standard power electronics: controlled rectifiers
Question 1142
Power ElectronicsFull Converters

For a single-phase fully controlled bridge with continuous current, increasing alpha beyond 90 degrees makes the average DC-side voltage?

  • ANegative
  • BAlways positive
  • CExactly zero for all alpha
  • DIndependent of alpha
Report an error
Correct Answer: A. Negative
Explanation: Since cos alpha becomes negative for 90°<alpha<180°, the converter's average DC voltage becomes negative; with suitable DC-side conditions this corresponds to inversion/regeneration.
Reference: Standard power electronics: full converters
Question 1145
Power ElectronicsSemi-Converters

Compared with a fully controlled bridge, a single-phase semi-converter uses?

  • ATwo SCRs and two diodes
  • BFour SCRs
  • CFour MOSFETs only
  • DOne SCR and three DIACs
Report an error
Correct Answer: A. Two SCRs and two diodes
Explanation: A conventional single-phase semi-converter is a half-controlled bridge containing two thyristors and two diodes.
Reference: Standard power electronics: semi-converters
Question 1146
Power ElectronicsFreewheeling Operation

For an RL load, a freewheeling diode can improve load-current continuity by conducting when?

  • AThe main rectifier path no longer supplies the inductive current
  • BThe load inductance becomes zero
  • CThe AC source is permanently disconnected
  • DThe gate pulse is at its maximum only
Report an error
Correct Answer: A. The main rectifier path no longer supplies the inductive current
Explanation: Stored magnetic energy in the load inductance maintains current through the freewheeling diode when the source-side device stops conducting.
Reference: Standard power electronics: freewheeling operation
Question 1147
Power ElectronicsFreewheeling Operation

When an ideal freewheeling diode conducts across an RL load, the load voltage is approximately?

  • AZero
  • BEqual to the negative supply peak
  • CTwice the supply peak
  • DInfinite
Report an error
Correct Answer: A. Zero
Explanation: The conducting ideal diode effectively shorts the load terminals for the freewheeling interval, making load voltage approximately zero while current circulates.
Reference: Standard power electronics: freewheeling operation
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Question 1152
Power ElectronicsDC-DC Converters

An ideal boost converter is used when the required DC output voltage is generally?

  • AGreater than the DC input voltage
  • BAlways zero
  • CLess than the input in every case
  • DAC rather than DC
Report an error
Correct Answer: A. Greater than the DC input voltage
Explanation: A boost converter raises the DC voltage magnitude under ideal continuous-conduction operation.
Reference: Standard power electronics: dc-dc converters
Question 1155
Power ElectronicsSwitching Losses

Switching loss in a practical semiconductor device occurs mainly during?

  • ATurn-on and turn-off transitions
  • BThe ideal OFF state only
  • CThe ideal ON state with zero voltage drop
  • DMechanical rotation
Report an error
Correct Answer: A. Turn-on and turn-off transitions
Explanation: During switching transitions, appreciable voltage and current coexist for finite time, producing energy loss.
Reference: Standard power electronics: switching losses
Question 1161
Power ElectronicsPWM Inverters

Sinusoidal PWM in an inverter is commonly obtained by comparing a low-frequency sinusoidal reference with a?

  • AHigh-frequency triangular carrier
  • BDC resistance
  • CSquare-wave load current only
  • DMechanical timing disk
Report an error
Correct Answer: A. High-frequency triangular carrier
Explanation: SPWM compares a sinusoidal modulating/reference signal with a higher-frequency triangular carrier to determine switching instants.
Reference: Standard power electronics: pwm inverters
Question 1162
Power ElectronicsPWM Inverters

In sinusoidal PWM, increasing the carrier frequency while keeping the fundamental reference frequency fixed generally moves dominant switching harmonics?

  • ATo higher frequencies
  • BTo DC
  • CExactly onto the fundamental
  • DTo zero frequency
Report an error
Correct Answer: A. To higher frequencies
Explanation: Higher carrier frequency shifts switching-related harmonic groups upward, which can simplify output filtering at the cost of higher switching losses.
Reference: Standard power electronics: pwm inverters
Question 1163
Power ElectronicsAC Voltage Controllers

A single-phase AC voltage controller with a resistive load commonly uses two antiparallel SCRs or a?

  • ATRIAC
  • BPower diode only
  • CZener diode
  • DBJT operated as a linear amplifier only
Report an error
Correct Answer: A. TRIAC
Explanation: A TRIAC provides bidirectional controlled conduction and can replace two antiparallel SCRs in many single-phase AC controllers.
Reference: Standard power electronics: ac voltage controllers
Question 1164
Power ElectronicsAC Voltage Controllers

With a purely resistive load in an AC voltage controller, increasing the firing angle generally causes the RMS load voltage to?

  • ADecrease
  • BIncrease above the source RMS without a transformer
  • CRemain constant
  • DBecome DC
Report an error
Correct Answer: A. Decrease
Explanation: A larger firing delay reduces the conduction interval in each half-cycle, lowering the RMS output voltage.
Reference: Standard power electronics: ac voltage controllers
Question 1165
Power ElectronicsDC-DC Converters

The ideal inverting buck-boost converter output voltage is given by?

  • AVo/Vs = -D/(1-D)
  • BVo/Vs = D
  • CVo/Vs = 1/(1-D)
  • DVo/Vs = 1-D
Report an error
Correct Answer: A. Vo/Vs = -D/(1-D)
Explanation: The basic inverting buck-boost converter produces an output of opposite polarity with magnitude D/(1-D) times the input.
Reference: Standard power electronics: dc-dc converters
Question 1168
Power ElectronicsSwitching Devices

A major advantage of operating a power semiconductor as a switch rather than in its linear region is?

  • AHigher conversion efficiency
  • BGuaranteed zero electromagnetic interference
  • CInfinite switching frequency
  • DNo need for protection circuits
Report an error
Correct Answer: A. Higher conversion efficiency
Explanation: Switch-mode operation ideally keeps either voltage or current small in the device, reducing power dissipation compared with linear control.
Reference: Standard power electronics: switching devices
Question 1169
Power ElectronicsPower MOSFET

For high-frequency low-to-medium voltage switching, a power MOSFET is often preferred because of its?

  • AFast switching capability
  • BNeed for continuous gate current
  • CLatching behavior like an SCR
  • DVery slow turn-off
Report an error
Correct Answer: A. Fast switching capability
Explanation: Power MOSFETs are majority-carrier devices and can switch rapidly, making them useful at relatively high switching frequencies.
Reference: Standard power electronics: power mosfet
Question 1170
Power ElectronicsIGBT

Compared with a power MOSFET, an IGBT is commonly attractive in applications requiring?

  • AHigher voltage and substantial power handling at moderate switching frequencies
  • BOnly microampere signal amplification
  • CNo gate drive at all
  • DBidirectional blocking without any circuit consideration
Report an error
Correct Answer: A. Higher voltage and substantial power handling at moderate switching frequencies
Explanation: IGBTs combine voltage-controlled gate drive with strong high-voltage/current capability, though typically at lower switching speeds than MOSFETs.
Reference: Standard power electronics: igbt
Question 1171
Power ElectronicsAC Power Control

Integral-cycle control regulates AC power by applying?

  • AComplete supply cycles to the load for some intervals and blocking complete cycles for others
  • BOnly one microsecond pulse per year
  • CA continuously variable DC voltage
  • DA different transformer turns ratio every half-cycle
Report an error
Correct Answer: A. Complete supply cycles to the load for some intervals and blocking complete cycles for others
Explanation: Integral-cycle or on-off control passes whole AC cycles during ON intervals and suppresses whole cycles during OFF intervals.
Reference: Standard power electronics: ac power control
Question 1172
Power ElectronicsAC Power Control

Integral-cycle control is particularly suitable for loads with relatively large thermal time constants, such as?

  • AElectric heaters
  • BHigh-frequency RF mixers
  • CSmall-signal microphone preamplifiers
  • DCrystal oscillators
Report an error
Correct Answer: A. Electric heaters
Explanation: Thermal loads respond slowly, so groups of complete AC cycles can regulate average heating power without requiring rapid output response.
Reference: Standard power electronics: ac power control
Question 1174
Power ElectronicsThree-Phase Rectifiers

Compared with a single-phase rectifier, a three-phase bridge generally provides?

  • ALower output ripple for comparable conditions
  • BOnly one output pulse per cycle
  • CNo DC component
  • DZero power capability
Report an error
Correct Answer: A. Lower output ripple for comparable conditions
Explanation: The higher pulse number of a three-phase bridge produces smoother DC and makes filtering easier.
Reference: Standard power electronics: three-phase rectifiers
Question 1175
Power ElectronicsCommutation Overlap

Source inductance in a practical controlled rectifier causes commutation overlap because?

  • ACurrent transfer between devices cannot occur instantaneously
  • BGate pulses become DC
  • CLoad resistance becomes infinite
  • DSupply frequency becomes zero
Report an error
Correct Answer: A. Current transfer between devices cannot occur instantaneously
Explanation: Inductance opposes instantaneous current change, so outgoing and incoming devices conduct simultaneously for a finite overlap interval.
Reference: Standard power electronics: commutation overlap
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Question 1177
Power ElectronicsCycloconverters

A cycloconverter is most commonly used to obtain an output frequency that is?

  • ALower than the input frequency
  • BAlways much higher than input
  • CExactly DC only
  • DIndependent of switching sequence
Report an error
Correct Answer: A. Lower than the input frequency
Explanation: Line-commutated cycloconverters are particularly suited to direct conversion from fixed-frequency AC to lower-frequency AC.
Reference: Standard power electronics: cycloconverters
Question 1178
Power ElectronicsCycloconverters

A major application of high-power cycloconverters is?

  • ALow-speed large AC motor drives
  • BSmall battery-powered calculators
  • CAudio microphone biasing
  • DDC resistance measurement only
Report an error
Correct Answer: A. Low-speed large AC motor drives
Explanation: Cycloconverters have historically been used in high-power, low-speed variable-frequency motor-drive applications.
Reference: Standard power electronics: cycloconverters
Question 1179
Power ElectronicsInverter Protection

In a voltage-source inverter, shoot-through of one bridge leg means?

  • AThe upper and lower switches of the same leg conduct simultaneously
  • BAll switches remain OFF
  • COnly the load current becomes zero
  • DThe DC source is disconnected safely
Report an error
Correct Answer: A. The upper and lower switches of the same leg conduct simultaneously
Explanation: Simultaneous conduction of both devices in one leg creates a very low-impedance path across the DC link and can damage the switches.
Reference: Standard power electronics: inverter protection
Question 1180
Power ElectronicsThree-Phase Rectifiers

For an ideal three-phase fully controlled bridge rectifier with continuous DC current, the average output voltage is commonly written as?

  • A1.35 VLL cos alpha
  • B0.45 VLL cos alpha
  • C2.34 VLL sin alpha
  • DVLL/(1-D)
Report an error
Correct Answer: A. 1.35 VLL cos alpha
Explanation: For a six-pulse three-phase full converter with continuous current and negligible overlap, Vdc=1.35 VLL cos alpha, where VLL is the RMS line-to-line input voltage.
Reference: Standard power electronics: three-phase rectifiers
Question 1187
Power ElectronicsDevice Selection

For high-voltage, high-power switching at moderate switching frequency, which device is commonly a suitable fully controllable choice?

  • AIGBT
  • BDIAC
  • CUncontrolled power diode
  • DConventional SCR with no turn-off circuit in every case
Report an error
Correct Answer: A. IGBT
Explanation: IGBTs are widely used where substantial voltage/current capability and gate-controlled turn-on/turn-off are required at moderate switching frequencies.
Reference: Standard power electronics: device selection
Question 1188
Power ElectronicsPower Factor

A controlled rectifier drawing a highly non-sinusoidal and phase-delayed input current can have reduced input power factor due to?

  • ABoth displacement and distortion effects
  • BOnly transformer turns ratio
  • COnly DC load resistance
  • DAntenna radiation loss
Report an error
Correct Answer: A. Both displacement and distortion effects
Explanation: Converter input power factor can be degraded by phase displacement of the fundamental current and by harmonic distortion of the input current waveform.
Reference: Standard power electronics: power factor
Question 1189
Power ElectronicsInverter Protection

Dead time in an inverter bridge is intentionally inserted mainly to prevent?

  • AShoot-through
  • BFundamental output voltage
  • CPWM operation
  • DLoad current flow in every interval
Report an error
Correct Answer: A. Shoot-through
Explanation: A short blanking interval between turning one switch OFF and its complementary switch ON prevents cross-conduction.
Reference: Standard power electronics: inverter protection
Question 1190
Power ElectronicsPWM Inverters

In sinusoidal PWM, the amplitude modulation index in the linear region is commonly the ratio of?

  • AReference sine amplitude to carrier amplitude
  • BCarrier frequency to reference frequency
  • CDC-link voltage to load current
  • DSwitching loss to conduction loss
Report an error
Correct Answer: A. Reference sine amplitude to carrier amplitude
Explanation: For carrier-based SPWM, amplitude modulation index ma is the peak reference/modulating signal divided by the peak carrier signal.
Reference: Standard power electronics: pwm inverters
Question 1192
Power ElectronicsPWM Inverters

In sinusoidal PWM, the frequency modulation ratio is commonly defined as?

  • ACarrier frequency divided by reference frequency
  • BReference amplitude divided by carrier amplitude
  • COutput voltage divided by input voltage
  • DLoad current divided by switch current
Report an error
Correct Answer: A. Carrier frequency divided by reference frequency
Explanation: mf=fc/fm, where fc is carrier frequency and fm is the desired fundamental/reference frequency.
Reference: Standard power electronics: pwm inverters
Question 1196
Power ElectronicsHarmonics

Total harmonic distortion (THD) is a measure of?

  • AHarmonic content relative to the fundamental component
  • BOnly DC input voltage
  • CSemiconductor junction temperature
  • DGate resistance
Report an error
Correct Answer: A. Harmonic content relative to the fundamental component
Explanation: THD quantifies the RMS contribution of harmonics relative to the RMS fundamental component.
Reference: Standard power electronics: harmonics
Question 1197
Power ElectronicsPWM Inverters

An output filter at a PWM inverter is mainly used to?

  • AAttenuate switching-frequency harmonics
  • BIncrease semiconductor layer count
  • CGenerate gate pulses
  • DEliminate the DC source
Report an error
Correct Answer: A. Attenuate switching-frequency harmonics
Explanation: The filter passes the desired low-frequency fundamental while reducing high-frequency switching components.
Reference: Standard power electronics: pwm inverters
Question 1198
Computer & Networking BasicsComputer Fundamentals

CPU stands for?

  • ACentral Processing Unit
  • BComputer Primary Utility
  • CCentral Program User
  • DControl Processing Utility
Report an error
Correct Answer: A. Central Processing Unit
Explanation: CPU stands for Central Processing Unit and executes instructions while coordinating major processing operations.
Reference: Standard computer and networking fundamentals: computer fundamentals
Question 1200
Computer & Networking BasicsComputer Fundamentals

Which CPU component directs and coordinates the execution of instructions?

  • AControl Unit
  • BHard disk
  • CMonitor
  • DNetwork cable
Report an error
Correct Answer: A. Control Unit
Explanation: The control unit interprets instructions and coordinates operations within the processor and other system components.
Reference: Standard computer and networking fundamentals: computer fundamentals
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