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 131 of 158
- A. white body
- B. grey body
- C. black body
- D. transparent body
Explanation: A white body reflects essentially all incident radiation, whereas a black body absorbs it and a transparent body transmits it.
Correct answer: white body- A. Eddy current heating
- B. Arc heating
- C. Induction heating
- D. Dielectric heating
Explanation: Dielectric heating uses a high-frequency alternating electric field to produce molecular agitation and heat inside insulating materials.
Correct answer: Dielectric heating- A. Arc heating
- B. Dielectric heating
- C. Induction heating
- D. Resistance heating
Explanation: Resistance heating has a purely resistive load, so its power factor is unity, the maximum possible value.
Correct answer: Resistance heating- A. Quicker operation
- B. Higher efficiency
- C. Absence of flue gases
- D. All of the above
Explanation: Electric heating provides rapid and efficient heat transfer and produces no combustion flue gases at the point of use.
Correct answer: All of the above- A. Resistance heating
- B. Dielectric heating
- C. Arc heating
- D. Induction heating
Explanation: Dielectric heating uses an insulating load that behaves predominantly capacitively, so its current leads the applied voltage.
Correct answer: Dielectric heating- A. Induction heating
- B. Dielectric heating
- C. Electric resistance heating
- D. All of the above
Explanation: Resistance heating depends mainly on the value of resistance and applied voltage, not on supply frequency.
Correct answer: Electric resistance heating- A. Rectifiers
- B. Motor converters
- C. Motor-generator sets
- D. Rotary converters
- E. All of the above
Explanation: AC can be changed to DC using static rectifiers or electromechanical systems such as motor converters, motor-generator sets, and rotary…
Correct answer: All of the above- A. Load
- B. Aluminium
- C. Copper
- D. Zinc
- E. None of the above
Explanation: Aluminium is commonly obtained industrially by electrolytic reduction of alumina in molten cryolite, since it cannot be extracted…
Correct answer: Aluminium- A. Motor-generator set
- B. Motor converter
- C. Rotary converter
- D. Mercury arc rectifier
Explanation: Historically, mercury-arc rectifiers were used for large-scale AC-to-DC conversion because they handled high voltage and current…
Correct answer: Mercury arc rectifier- A. Illumination
- B. Electrolysis
- C. Variable speed operation
- D. Traction
Explanation: Electrolysis requires a unidirectional flow of current so that ions consistently move toward their respective electrodes and chemical…
Correct answer: Electrolysis- A. anode
- B. cathode
- C. shell bottom
- D. mercury pool
Explanation: Positive ions are attracted to the negatively charged cathode because opposite charges attract.
Correct answer: cathode- A. Telephones
- B. Relays
- C. Time switches
- D. All of the above
Explanation: Telephones use DC for their line supply, while relays and many time switches require DC to energise their coils or control mechanisms.
Correct answer: All of the above- A. 0.05 V to 0.2 V per cm length of the arc
- B. 0.5 V to 1.5 V per cm length of the arc
- C. 2 V to 3.5 V per cm length of the arc
- D. none of the above
Explanation: The arc voltage gradient in a mercury arc rectifier is comparatively high, typically about 2 to 3.5 V per centimetre of arc length.
Correct answer: 2 V to 3.5 V per cm length of the arc- A. its ionization potential is relatively low
- B. its atomic weight is quite high
- C. its boiling point and specific heat are low
- D. it remains in liquid state at ordi¬nary temperature
- E. all of the above
Explanation: Mercury is suitable as a cathode because it is liquid at room temperature, has relatively low ionisation potential, and its heavy atoms…
Correct answer: all of the above- A. 100 A at 100 V
- B. 200 A at 200 V
- C. 300 A at 300 V
- D. 400 A at 400 V
- E. 500 A at 500 V
Explanation: Glass mercury-arc rectifiers were commonly manufactured for high-current, high-voltage service, with standard maximum continuous ratings…
Correct answer: 500 A at 500 V- A. expenditure of energy in ionization
- B. surface resistance
- C. expenditure of energy in overcoming the electrostatic field
- D. expenditure of energy in liberating electrons from the mercury
Explanation: The cathode fall is the energy needed to liberate electrons from the mercury surface and establish emission at the cathode spot.
Correct answer: expenditure of energy in liberating electrons from the mercury- A. anode is heated
- B. tube is evacuated
- C. an auxiliary electrode is used
- D. low mercury vapour pressures are used
Explanation: An auxiliary electrode is used to initiate ionisation and establish the cathode spot in a mercury arc rectifier.
Correct answer: an auxiliary electrode is used- A. it is light in weight and occupies small floor space
- B. it has high efficiency
- C. it has high overload capacity
- D. it is comparatively noiseless
- E. all of the above
Explanation: Mercury arc rectifiers combine high efficiency, strong overload capability, quiet operation, and relatively compact construction.
Correct answer: all of the above- A. voltage only
- B. current only
- C. voltage and current
- D. r.m.s. value of current
- E. none of the above
Explanation: Internal efficiency is mainly determined by the ratio of the useful rectified voltage to the supply voltage, so it depends primarily on…
Correct answer: voltage only- A. is directly proportional to load
- B. is inversely proportional to load
- C. varies exponentially with the load current
- D. is almost independent of load current
Explanation: The arc and electrode voltage drops in a mercury pool rectifier remain nearly constant over its normal operating-current range.
Correct answer: is almost independent of load current