All Free Electrical Engineering MCQs with Answers
Every Electrical Engineering question in the bank, across all chapters, each with the correct answer and a written explanation. Free and unlimited, with no account needed.
3,143 questions · page 137 of 158
- A. Voltage mode control
- B. Current mode control
- C. Hysteric control
- D. All of these
Explanation: PWM DC-DC converters may use voltage-mode control, current-mode control, or hysteretic control.
Correct answer: All of these- A. Large overlapping takes place
- B. Small overlapping operation
- C. No overlapping operation
- D. None of these
Explanation: In voltage commutation, the commutation capacitor applies reverse voltage to turn off the outgoing thyristor before the incoming device…
Correct answer: No overlapping operation- A. V 0 = V s
- B. V 0 = D V s
- C. V 0 = V s / D
- D. V 0 = V s / ( 1 - D )
Explanation: For an ideal step-down chopper, the switch applies the source for a fraction D of each switching period.
Correct answer: V 0 = D V s- A. AC - DC converters
- B. AC - AC converters
- C. DC - AC converters
- D. DC - DC converters
Explanation: A chopper uses semiconductor switching to convert a fixed DC voltage into a controlled DC voltage.
Correct answer: DC - DC converters- A. Only at turn - on
- B. Only at turn - off
- C. Both at turn on and off
- D. None of these
Explanation: A BJT dissipates switching energy during both turn-on and turn-off because voltage and current overlap during each transition.
Correct answer: Both at turn on and off- A. Negative resistance characteristics
- B. Goes into avalanche condition
- C. Voltage drop snaps back
- D. All of these
Explanation: At its breakover voltage, a DIAC enters avalanche conduction, its voltage drops sharply, and its current-voltage curve shows a…
Correct answer: All of these- A. Diode and capacitor
- B. Capacitor and SCR
- C. Inductor and capacitor
- D. Capacitor and load
Explanation: In the standard commutation circuits, interchanging the diode and capacitor changes the commutation arrangement from voltage commutation…
Correct answer: Diode and capacitor- A. Equal to the input frequency
- B. Twice the input frequency
- C. Three times the input frequency
- D. Six times the input frequency
Explanation: A three-phase bridge is a six-pulse rectifier, so six ripple peaks occur in every input cycle.
Correct answer: Six times the input frequency- A. Symmetric triangular voltage across itself
- B. Symmetric rectangular voltage across itself
- C. Symmetric trapezoidal voltage across itself
- D. Symmetric sinusoidal voltage across itself
Explanation: In load commutation, the resonant load causes the capacitor voltage to rise and fall through approximately linear portions with changing…
Correct answer: Symmetric trapezoidal voltage across itself2730. 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
Explanation: During current commutation, the commutating inductance voltage collapses while the charged commutating capacitor can add its voltage to…
Correct answer: Both A. and B.- A. Single phase
- B. 3 phase
- C. Poly phase
- D. Only (b) and (c)
Explanation: For outputs above about 15 kW, three-phase or polyphase rectifiers are preferred because they provide smoother DC and lower ripple current…
Correct answer: Only (b) and (c)- A. 61%
- B. 71%
- C. 81%
- D. 91%
Explanation: The rectification efficiency of an ideal full-wave rectifier is about 81.2%, obtained from the ratio of DC output power to AC input power.
Correct answer: 81%- A. rectifier
- B. inverter
- C. chopper
- D. regulator
Explanation: A single-phase AC-to-DC converter changes alternating voltage into unidirectional voltage, which is the rectification process.
Correct answer: rectifier- A. anode current decreases
- B. anode current does not decrease at all
- C. anode current increases
- D. cathode current increases
Explanation: Once an SCR has been triggered and latched, removing the gate signal does not turn it off.
Correct answer: anode current does not decrease at all- 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
Explanation: For forward operation of an SCR, the anode must be at a higher potential than the cathode, while the gate pulse initiates conduction.
Correct answer: Always positive w.r.t cathode- A. Across anode
- B. In series with anode
- C. Across cathode
- D. In series with cathode
Explanation: The load is placed in series with the SCR's anode-cathode conduction path so that anode current flows through the load.
Correct answer: In series with anode- A. Two
- B. Three
- C. Four
- D. Five
Explanation: An SCR has a four-layer PNPN structure, which produces three PN junctions between the layers.
Correct answer: Three- A. Insulated gate bipolar transistor
- B. Insulated gate bidirectional transistor
- C. Inductive gate bipolar transistor
- D. Inductive gate bidirectional transistor
Explanation: IGBT expands to Insulated Gate Bipolar Transistor. It combines the voltage-controlled insulated gate of a MOSFET with the low conduction…
Correct answer: Insulated gate bipolar transistor- 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
Explanation: An ideal switch has zero power loss, can conduct current in either direction when on, and blocks current in either direction when off.
Correct answer: All of these- A. Indirect switch matrix circuits
- B. Direct switch matrix circuits
- C. Embedded converters
- D. All of these
Explanation: A rectifier performs direct AC-to-DC conversion, and adding an external low-pass filter does not change it into a two-stage indirect…
Correct answer: Direct switch matrix circuits