All Free Electrical Engineering MCQs with Answers

• 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…

• 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…

• 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…

• 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.

• 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…

• 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…

• 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…

• 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…

• 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.

• 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…

• 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.

• 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…

• 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.

• 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.

• 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…

• 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…

• 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.

• 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…

• 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.

• 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.