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 18 of 54
- A. Lead-acid cell, Edison cell, Nickel cadmium cell
- B. Lead-acid cell, Nickel-cadmium cell, Edison cell
- C. Edison cell, Nickel-cadmium cell, lead-acid cell
- D. Nickel-cadmium cell, Edison cell, lead-acid cell
Explanation: Typical service life increases from lead-acid batteries to Edison nickel-iron cells and then to nickel-cadmium cells.
Correct answer: Lead-acid cell, Edison cell, Nickel cadmium cell- A. equal to that of large dry cell
- B. less than that of large dry cell
- C. more than that of large dry cell
- D. none of the above
Explanation: A larger dry cell contains more active material and electrolyte, so it generally remains usable for a longer storage period.
Correct answer: less than that of large dry cell- A. below
- B. equal to
- C. above
- D. none of the above
Explanation: The electrolyte must cover the plates completely so their active material remains immersed and can participate in the chemical reaction.
Correct answer: above- A. colour
- B. mass
- C. viscosity
- D. specific gravity
Explanation: In a lead-acid battery, charging converts water and lead sulphate into sulphuric acid, increasing the electrolyte's specific gravity.
Correct answer: specific gravity- A. in well ventilated location
- B. in clean and dry place
- C. as near as practical to the battery being charged
- D. in location having all above features
Explanation: Charging batteries can release corrosive gases, so the equipment needs ventilation and a clean, dry location.
Correct answer: in location having all above features- A. rectifiers
- B. engine generator sets
- C. motor generator sets
- D. any one of the above methods
Explanation: A battery charger needs a DC source, which may be obtained from rectifiers, engine-generator sets, or motor-generator sets.
Correct answer: any one of the above methods- A. decreases
- B. increases
- C. remains constant
- D. none of the above
Explanation: With constant-current charging, the charger must raise its output voltage as the battery's terminal voltage increases during charging.
Correct answer: increases- A. Loss of capacity
- B. Loss of life
- C. Corrosion of the grids of the plate
- D. All above
Explanation: Excessively high specific gravity makes the electrolyte more corrosive, which accelerates grid corrosion and shortens battery life; it can…
Correct answer: All above- A. capacity of the cell is reduced
- B. life of the cell is reduced
- C. open plates are converted to lead sulphate
- D. all above
Explanation: Exposed plates lose active electrolyte contact, reducing capacity and accelerating deterioration.
Correct answer: all above- A. decreases
- B. increases
- C. remains constant
- D. none of the above
Explanation: With constant-voltage charging, the battery initially draws a high current because its terminal voltage is low.
Correct answer: decreases- A. to allow gases out when the cell is on charge
- B. to add water to the cell if needed
- C. to check the level of electrolyte
- D. to do all above functions
Explanation: A vent cap permits charging gases to escape, provides access for adding distilled water, and allows the electrolyte level to be inspected.
Correct answer: to do all above functions- A. positive active material
- B. negative active material
- C. passive material
- D. none of the above
Explanation: In a lead-acid cell, the negative plate is made chiefly of spongy lead, so lead is the negative active material.
Correct answer: negative active material- A. increases
- B. decreases
- C. remains same
- D. none of the above
Explanation: Sulphation forms hard lead-sulphate deposits on the plates, reducing the effective active area and hindering chemical action.
Correct answer: increases- A. 1.8 V
- B. 1.9 V
- C. 2 V
- D. 2.1 V
Explanation: A lead-acid cell should generally not be discharged below about 1.8 V per cell, since deeper discharge promotes sulphation and may…
Correct answer: 1.8 V355. Excessive formation of lead sulphate on the surface of the plates happens because of___________?
- A. allowing a battery to stand in discharged condition for a long time
- B. topping up with electrolyte
- C. persistent undercharging
- D. low level of electrolyte
- E. all above
Explanation: Leaving a battery discharged, persistent undercharging, an inadequate electrolyte level, or using electrolyte improperly for topping up…
Correct answer: all above- A. active
- B. passive
- C. inert
- D. dielectric
Explanation: The substances that undergo chemical changes during charging and discharging to store and release electrical energy are called active…
Correct answer: active- A. reduces specific gravity of the electrolyte
- B. increases specific gravity of the electrolyte
- C. produces excessive gassing
- D. increases the temperatureHire Civil Engineers
Explanation: Undercharging leaves some lead sulphate unconverted and keeps the charging reaction incomplete, so the electrolyte remains less…
Correct answer: reduces specific gravity of the electrolyte- A. two rate charge control
- B. trickle charge
- C. floating charge
- D. an equalizing charge
Explanation: A two-rate charge-control system switches or regulates the charging current between upper and lower limits, preventing excessive current…
Correct answer: two rate charge control- A. amperes
- B. ampere-hours
- C. watts
- D. watt-hours
Explanation: Battery capacity is the amount of charge it can deliver, calculated as current multiplied by time, so its unit is ampere-hour (Ah).
Correct answer: ampere-hours- A. produces excessive gassing
- B. loosens the active material
- C. increases the temperature resulting in buckling of plates
- D. all above
Explanation: Overcharging causes excessive gassing, heats the cell and may buckle the plates; it can also loosen the active material.
Correct answer: all above