Free Electrical Machines MCQs with Answers
1,061 Electrical Machines 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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1,061 questions · page 20 of 54
- A. corrosive fumes are produced
- B. water is neither formed nor absorbed
- C. nickel hydroxide remains unsplit
- D. its e.m.f. remains constant
Explanation: In a nickel-iron cell, the charging and discharging reactions transfer oxygen between the electrode compounds without a net formation or…
Correct answer: water is neither formed nor absorbed- A. adding distilled water
- B. adding so-called battery restorer
- C. a dose of H2SO4
- D. none of the above
Explanation: A genuinely dead or permanently damaged storage battery cannot normally be restored by adding water, acid, or a marketed battery restorer…
Correct answer: none of the above- A. 1 V
- B. 1.5 V
- C. 1.75 V
- D. 2 V
Explanation: Parallel connection keeps the voltage equal to that of one cell while increasing the available current capacity.
Correct answer: 2 V- A. current rating
- B. voltage rating
- C. ampere-hour rating
- D. none of the above
Explanation: Battery capacity is the quantity of charge that can be delivered and is specified in ampere-hours, calculated approximately as current…
Correct answer: ampere-hour rating- A. increase the voltage rating
- B. increase the current rating
- C. increase the life of the cells
- D. none of the above
Explanation: In a series connection, the same current flows through every cell and the cell voltages add together.
Correct answer: increase the voltage rating- A. output voltage
- B. temperature of electrolyte
- C. specific gravity of electrolyte
- D. none of the above
Explanation: Specific gravity changes predictably with the concentration of sulphuric acid, so it gives a more reliable indication of state of charge…
Correct answer: specific gravity of electrolyte- A. less than the battery voltage
- B. higher than the battery voltage
- C. the same as the battery voltage
- D. none of the above
Explanation: The charger must provide a voltage greater than the battery's terminal voltage so that charging current flows into the battery.
Correct answer: higher than the battery voltage388. The ratio of ampere-hour efficiency to watt-hour efficiency of a lead-acid cell is____________?
- A. just one
- B. always greater than one
- C. always less than one
- D. none of the above
Explanation: Watt-hour efficiency is lower than ampere-hour efficiency because charging and discharging involve voltage losses.
Correct answer: always greater than one- A. nickel-cadmium battery
- B. zinc-carbon battery
- C. lead-acid battery
- D. none of the above
Explanation: Lead-acid batteries are widely used in power stations for substation control, relay operation, circuit-breaker tripping and emergency…
Correct answer: lead-acid battery- A. its voltage increases
- B. it gives out energy
- C. its cathode becomes dark chocolate brown in colour
- D. specific gravity of H2SO4 decreases
Explanation: During charging, electrical energy converts lead sulphate back into lead and lead peroxide, causing the cell voltage and the electrolyte's…
Correct answer: its voltage increases- A. lead and lead peroxide
- B. lead sulphate and lead
- C. lead peroxide and lead
- D. none of the above
Explanation: A fully charged lead-acid cell has lead peroxide (PbO₂) on its positive plate and spongy lead (Pb) on its negative plate.
Correct answer: lead peroxide and lead- A. temperature
- B. rate of charge
- C. rate of discharge
- D. quantity of active material
Explanation: Cell capacity is affected by temperature, discharge rate and the amount of active material; the standard rated capacity is not determined…
Correct answer: rate of charge393. The charge required to liberate one gram equivalent of any substance is known as _________ constant
- A. time
- B. Faraday's
- C. Boltzman
Explanation: Faraday's constant is the charge needed to liberate one gram-equivalent of a substance during electrolysis, approximately 96,500 coulombs.
Correct answer: Faraday's- A. dark grey
- B. brown
- C. dark brown
- D. none of above
Explanation: The fully charged positive plate contains lead peroxide, whose characteristic colour is dark brown or chocolate brown.
Correct answer: dark brown- A. Newton's law
- B. Faraday's law of electromagnetic
- C. Faraday's law of electrolysis
- D. Gauss's law
Explanation: Faraday's first law of electrolysis states that the mass deposited or liberated at an electrode is directly proportional to the quantity…
Correct answer: Faraday's law of electrolysis- A. iron loss in core
- B. skin effect
- C. increase in temperature
- D. capacitive effect between adjacent coil turns
Explanation: An iron-cored choke has core losses, such as hysteresis and eddy-current losses, which can be represented as an additional effective…
Correct answer: iron loss in core- A. reduce eddy current loss
- B. increase heat radiation
- C. make assembly cheap and easier
- D. reduce circuit permeability
Explanation: Laminating an iron core breaks up the paths available for circulating eddy currents, greatly reducing eddy-current loss.
Correct answer: reduce eddy current loss- A. synchronous condenser
- B. generator
- C. induction motor
- D. alternator
Explanation: An overexcited synchronous motor draws leading current and supplies reactive power; when operating without mechanical load, it performs…
Correct answer: synchronous condenser- A. rated r.p.m.
- B. no load
- C. 20 percent load
- D. near full load
Explanation: An induction motor draws substantial magnetising current at light load, giving a poor power factor.
Correct answer: near full load- A. nuclear power plants
- B. hydraulic turbines
- C. diesel engines
- D. steam accumulators
- E. none of the above
Explanation: Diesel engines are widely used for ship propulsion because they provide high torque, good fuel economy, and practical operation at marine…
Correct answer: diesel engines