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 19 of 54
- A. its chemical constituents
- B. on the strength of its electrolyte
- C. its temperature
- D. all above
Explanation: Cell open-circuit voltage is governed by the electrode and electrolyte chemistry, while electrolyte strength and temperature also affect…
Correct answer: all above- A. NaOH
- B. onlyH2S04
- C. only water
- D. dilute H2SO4
Explanation: A lead-acid cell uses sulfuric acid diluted with water as its electrolyte.
Correct answer: dilute H2SO4- A. charged state
- B. discharged state
- C. both (A) and (B)
- D. active state
Explanation: During discharge, sulfuric acid is consumed and water is formed, so the electrolyte specific gravity falls.
Correct answer: discharged state- A. copper
- B. lead
- C. iron
- D. silver oxide
Explanation: The Edison, or nickel-iron, cell uses iron as the negative-plate material and nickel oxide as the positive material.
Correct answer: iron- A. less than
- B. more than
- C. equal to
- D. none of the above
Explanation: Lead-acid cells have lower internal resistance than Edison cells, allowing them to supply comparatively larger current.
Correct answer: less than- A. NaOH
- B. KOH
- C. HC1
- D. HN03
Explanation: The Edison cell uses potassium hydroxide, KOH, as its alkaline electrolyte.
Correct answer: KOH- A. 40%
- B. 60%
- C. 70%
- D. 80%
Explanation: An Edison nickel-iron cell has a relatively low ampere-hour efficiency because charging losses and gas evolution are significant; its…
Correct answer: 80%- A. 1.4 V
- B. 1 V
- C. 0.9 V
- D. 0.8 V
Explanation: A fully charged Edison cell has a nominal e.m.f. of about 1.4 V, higher than the approximately 1.2 V value associated with its normal…
Correct answer: 1.4 V- A. two
- B. three
- C. four
- D. five
Explanation: Alkaline cells generally have higher internal resistance than lead-acid cells, commonly taken as approximately five times as high in…
Correct answer: five- A. rate of discharge
- B. temperature
- C. density of electrolyte
- D. quantity of active materials
- E. all above
Explanation: Cell capacity changes with discharge rate, temperature, electrolyte density, and the amount of active material, so all the listed factors…
Correct answer: all above- A. 20 to 30%
- B. 40 to 50%
- C. 60 to 70%
- D. 90 to 95%
Explanation: Lead-acid batteries have a high ampere-hour efficiency, normally around 90 to 95%; their watt-hour efficiency is lower because of voltage…
Correct answer: 90 to 95%- A. dull
- B. reddish
- C. bright
- D. milky
Explanation: Near full charge, vigorous gassing produces many fine gas bubbles in the electrolyte, giving it a milky appearance.
Correct answer: milky- A. silver oxide
- B. lead oxide
- C. lead
- D. zinc powder
Explanation: In a silver-zinc cell, silver oxide forms the positive-plate active material, while zinc serves as the negative-plate material.
Correct answer: silver oxide- A. 1 V
- B. 1.2 V
- C. 1.7 V
- D. 2.1 V
Explanation: An alkaline cell has a nominal voltage near 1.2 V, but its average charging voltage is about 1.7 V because charging must overcome its…
Correct answer: 1.7 V- A. 25 to 35%
- B. 40 to 60%
- C. 70 to 80%
- D. 90 to 95%
Explanation: Lead-acid watt-hour efficiency is typically about 70 to 80%, lower than ampere-hour efficiency because the discharge voltage is lower than…
Correct answer: 70 to 80%- A. maintain proper electrolyte level
- B. increase its reserve capacity
- C. prevent sulphation
- D. keep it fresh and fully charged
Explanation: Trickle charging supplies a small continuous current that compensates for self-discharge and keeps the storage battery fresh and fully…
Correct answer: keep it fresh and fully charged- A. there is a rise in voltage
- B. energy is absorbed by the cell
- C. specific gravity of H2SO4 is increased
- D. the anode becomes chocolate brown in colour (PbCfe) and cathode becomes grey metallic lead (Pb)
- E. all of the above
Explanation: During charging, electrical energy is stored chemically, the terminal voltage and electrolyte specific gravity rise, and lead sulfate…
Correct answer: all of the above378. As compared to a lead-acid cell, the efficiency of a nickel-iron cell is less due to its__________?
- A. compactness
- B. lower e.m.f.
- C. small quantity of electrolyte used
- D. higher internal resistance
Explanation: Nickel-iron cells have relatively high internal resistance, causing greater internal voltage drop and energy loss than in lead-acid cells.
Correct answer: higher internal resistance- A. one part H2O, three parts H2SO4
- B. two parts H2O, two parts H2SO4
- C. three parts H2O, one part H2SO4
- D. all H2S04
Explanation: The electrolyte is commonly prepared with approximately three parts water and one part sulfuric acid by volume, although its exact…
Correct answer: three parts H2O, one part H2SO4- A. passive
- B. active
- C. redundant
- D. inert
Explanation: Active materials are the substances that undergo the required chemical reactions during charging and discharging to store or release…
Correct answer: active