Free Power Electronics MCQs with Answers
253 Power Electronics MCQs from Electrical Engineering, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
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253 questions · page 2 of 13
- A. Is decreased
- B. Is increased
- C. Remains the same
- D. None of the above
Explanation: Increasing gate current assists regenerative turn-on, so the required anode-cathode breakover voltage decreases.
Correct answer: Is decreased- A. Changing anode voltage
- B. Changing gate voltage
- C. Reverse biasing the gate
- D. None of the above
Explanation: The firing instant, and therefore the conduction angle, is controlled by the gate trigger signal, commonly adjusted through gate voltage…
Correct answer: Changing gate voltage- A. Exactly zero
- B. Small leakage current
- C. Large leakage current
- D. None of the above
Explanation: An OFF SCR blocks the applied voltage but permits a small leakage current through its reverse- or forward-blocking junctions.
Correct answer: Small leakage current- A. Two SCRs in series
- B. Two SCRs in parallel
- C. Two SCRs in parallel opposition
- D. None of the above
Explanation: Two SCRs connected in anti-parallel, or parallel opposition, conduct on alternate half-cycles and allow bidirectional AC power control.
Correct answer: Two SCRs in parallel opposition- A. Remains the same
- B. Is increased
- C. Is decreased
- D. None of the above
Explanation: Increasing the firing angle delays SCR turn-on, leaving less of each cycle for conduction and generally reducing the rectifier's average…
Correct answer: Is decreased- A. Positive half-cycles only
- B. Negative half-cycles only
- C. Both positive and negative half-cycles
- D. Positive or negative half-cycles
Explanation: An SCR conducts only when forward biased and triggered, so its orientation determines whether it controls the positive or negative…
Correct answer: Positive or negative half-cycles- A. Gate
- B. Cathode
- C. Anode
- D. None of the above
Explanation: After an SCR is triggered and latches into conduction, removing the gate signal does not turn it off; the anode current must fall below…
Correct answer: Gate- A. 400/√2 V
- B. 400 V
- C. 400 x √2 V
- D. none of the above
Explanation: The stated rms input is 400/√2 V, so its peak value is 400 V. A half-wave rectifier diode must withstand this peak reverse voltage, making…
Correct answer: 400 V- A. half-wave rectifier
- B. centre-tap full-wave rectifier
- C. bridge full-wave rectifier
- D. none of the above
Explanation: A centre-tap full-wave rectifier requires a centre-tapped transformer secondary to provide the two equal, opposite half-cycle voltages.
Correct answer: centre-tap full-wave rectifier- A. components are expensive
- B. diodes must have a higher power rating
- C. output is difficult to filter
- D. none of the above
Explanation: A half-wave rectifier produces a large ripple with a low ripple frequency, so smoothing it requires more filtering.
Correct answer: output is difficult to filter- A. lighting purposes
- B. heaters
- C. using in electronic equipment
- D. none of the above
Explanation: Electronic equipment commonly requires a regulated dc supply, while the mains supply is normally ac, so a rectifier and filtering stages…
Correct answer: using in electronic equipment- A. twice
- B. thrice
- C. four time
- D. one-half
Explanation: With the same total secondary voltage, a centre-tap rectifier uses only half the secondary winding during each half-cycle, while a bridge…
Correct answer: one-half- A. 27.5 V
- B. 86.5 V
- C. 30 V
- D. 42.5 V
Explanation: The transformer secondary voltage is 240/8 = 30 V rms, so its peak value is 30√2 ≈ 42.5 V.
Correct answer: 42.5 V- A. choke input
- B. capacitor input
- C. resistance input
- D. none of the above
Explanation: A choke-input filter maintains conduction over a larger part of the cycle and produces a smaller change in output voltage with load…
Correct answer: choke input- A. one-half
- B. the same as
- C. twice
- D. four times
Explanation: For the same transformer secondary peak voltage, each bridge diode withstands only the secondary peak voltage, whereas each centre-tap…
Correct answer: one-half- A. solid state
- B. vacuum tube
- C. gas tube
- D. none of the above
Explanation: Solid-state rectifiers use semiconductor junctions with a much smaller forward voltage drop and resistance than vacuum-tube or gas-tube…
Correct answer: solid state- A. lower melting point
- B. higher temperature coefficient
- C. high specific resistance
- D. all of the above
Explanation: A furnace element should have high specific resistance so it produces substantial heat with a practical length and current.
Correct answer: high specific resistance- A. arc heating
- B. resistance heating
- C. induction heating
- D. dielectric heating
Explanation: A room heat convector passes current through a resistive element, converting electrical energy into heat by the Joule effect.
Correct answer: resistance heating39. Which of the following will happen if the thickness of refractory wall of furnace is increased ?
- A. Heat loss through furnace wall will increase
- B. Temperature inside the furnace will fall
- C. Temperature on the outer surface of furnace walls will drop
- D. Energy consumption will increase
Explanation: Increasing refractory thickness increases thermal resistance, reducing heat flow and lowering the temperature reached at the outer wall…
Correct answer: Temperature on the outer surface of furnace walls will drop40. A non-dimensional number generally associated with natural convection heat transfer is____________?
- A. Prandtl number
- B. Grashoff number
- C. Pecelet number
- D. Nusselt number
Explanation: The Grashof number compares buoyancy forces with viscous forces and is the key dimensionless number for natural convection.
Correct answer: Grashoff number