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 132 of 158
- A. the rectifier will not operate
- B. internal losses will be reduced
- C. both ion and electron streams will move in the same direction
- D. the rectifier will operate at reduced efficiency
Explanation: The mercury pool is designed to act as the cathode, while the carbon electrodes act as anodes.
Correct answer: the rectifier will not operate- A. self restoring property of mercury
- B. high ionization potential
- C. energy spent in overcoming the electrostatic field
- D. high temperature inside the rectifier
Explanation: Anode drop occurs because charged particles must expend energy in overcoming the electrostatic field near the anode.
Correct answer: energy spent in overcoming the electrostatic field- A. anode drop and cathode drop
- B. anode drop and arc drop
- C. cathode drop and arc drop
- D. anode drop, cathode drop and arc drop
Explanation: The anode-to-cathode voltage includes the voltage drop near the anode, the cathode drop, and the drop through the arc column.
Correct answer: anode drop, cathode drop and arc drop- A. 5.4 V
- B. 8.4 V
- C. 10.4 V
- D. 16.4 V
Explanation: Mercury has an ionization potential of approximately 10.4 V, commonly stated as 10.4 eV when expressed as ionization energy per electron.
Correct answer: 10.4 V- A. 2000 A
- B. 1500 A
- C. 1000 A
- D. 500 A
Explanation: Glass-bulb mercury arc rectifiers are limited by the mechanical and thermal capability of the glass enclosure and are commonly rated up to…
Correct answer: 500 A- A. colour of mercury
- B. ionization
- C. high temperature
- D. electron streams
Explanation: The characteristic blue glow is produced by the ionized mercury vapour in the arc.
Correct answer: ionization- A. Voltage drop in transformer reactance
- B. Voltage drop in resistance of transformer and smoothing chokes
- C. Arc voltage drop
- D. All of the above
Explanation: Under load, voltage is lost in transformer reactance, transformer and smoothing-choke resistance, and the rectifier arc itself.
Correct answer: All of the above- A. Six-phase
- B. Three-phase
- C. Two-phase
- D. Single-phase
Explanation: A six-phase rectifier produces six voltage pulses per cycle, so the intervals between pulses are shortest and the output ripple is least.
Correct answer: Six-phase- A. one-third of a cycle
- B. one-fourth of a cycle
- C. one-half a cycle
- D. two-third of a cycle
Explanation: In a three-phase rectifier, the three anodes share one complete cycle equally. Therefore, each anode conducts for one-third of a cycle.
Correct answer: one-third of a cycle- A. ions
- B. electrons
- C. ions and electrons
- D. any of the above
Explanation: The mercury arc contains positive mercury ions moving from the anode towards the cathode, while electrons move in the opposite direction.
Correct answer: ions- A. accelerates
- B. decelerates
- C. any of the above
- D. none of the above
Explanation: A grid made positive with respect to the cathode attracts electrons and increases their velocity towards the anode.
Correct answer: accelerates- A. The voltage regulation of the rec¬tifier should be low
- B. In the output circuit there should be no harmonics
- C. The power factor of the system should be high
- D. The rectifier supply transformer should be utilized to the best ad-vantage
- E. all of the above
Explanation: The number of phases is selected by considering ripple and harmonics, voltage regulation, power factor, and effective use of the supply…
Correct answer: all of the above- A. resistance
- B. capacitance
- C. leakage reactance
- D. any of the above
Explanation: During commutation, current transfer between phases is opposed mainly by the transformer’s leakage reactance.
Correct answer: leakage reactance- A. shunt motor
- B. synchronous motor
- C. induction regulator
- D. synchronous generator
Explanation: An induction regulator can vary the phase of its output voltage relative to the supply voltage, providing the required phase shift between…
Correct answer: induction regulator- A. maximum grid voltage
- B. critical grid voltage
- C. any of the above
- D. none of the above
Explanation: The minimum grid potential at which the anode-cathode arc can be initiated is called the critical grid voltage.
Correct answer: critical grid voltage- A. magnitude
- B. polarity
- C. phase
- D. any of the above
- E. none of the above
Explanation: Phase-shift control changes the firing instant relative to the AC waveform, so the effective phase of the applied grid voltage is varied.
Correct answer: phase2637. The metal rectifiers are preferred to valve rectifiers due to which of the following advantages ?
- A. They are mechanically strong
- B. They do not require any voltage for filament heating
- C. Both (A) and (B)
- D. None of the above
Explanation: Metal rectifiers are rugged because they have no fragile vacuum envelope, and they require no filament-heating supply.
Correct answer: Both (A) and (B)- A. 10°C
- B. 20°C
- C. 30°C
- D. 45°C
Explanation: Copper oxide rectifiers are strongly temperature-sensitive and are generally designed for operation up to about 45°C.
Correct answer: 45°C- A. 5 to 10 per cent
- B. 15 to 20 per cent
- C. 25 to 30 per cent
- D. none of the above
Explanation: Ageing in selenium rectifiers gradually changes the selenium junction characteristics, commonly producing about a 5 to 10 percent change…
Correct answer: 5 to 10 per cent- A. 90 to 95%
- B. 85 to 90%
- C. 80 to 85%
- D. 65 to 75%
Explanation: Copper oxide rectifiers have relatively high forward voltage loss and limited current capability, so their efficiency seldom exceeds…
Correct answer: 65 to 75%