Free Electrical Machines MCQs with Answers

• A. Lithium
• B. Zinc-chloride
• C. Mercury
• D. Carbon-zinc

Explanation: A mercury cell has a nominal voltage of about 1.35 V, lower than the roughly 1.5 V of zinc-chloride and carbon-zinc cells.

• A. buckling of plates
• B. faulty separators
• C. lead particles forming circuit between positive and negative plates
• D. excessive accumulation of sediment
• E. any one of aboveElectricity

Explanation: An internal short circuit can result from buckled plates, defective separators, conductive lead particles, or accumulated sediment…

• A. no
• B. very little
• C. less
• D. more

Explanation: Sulfation increases the battery's internal resistance, so charging current produces greater I²R heating.

• A. 1.0
• B. 1.5
• C. 2.4
• D. 2.9

Explanation: A lead-acid cell falls by about 0.4 V from its fully charged condition to its fully discharged condition.

• A. 0.8
• B. 0.95
• C. 1.1
• D. 1.21

Explanation: The Edison, or nickel-iron, cell uses potassium hydroxide electrolyte with a specific gravity commonly taken as about 1.21.

• A. Pb02
• B. PbSC-4
• C. PbO
• D. Pb

Explanation: During prolonged idling, the sulfuric acid electrolyte reacts with the lead-based active material and forms lead sulfate, PbSO₄.

• A. bakelite
• B. rubber
• C. nickel plated steel
• D. aluminium

Explanation: An Edison cell uses a nickel-plated steel container, which provides mechanical strength and improved resistance to the alkaline…

• A. 8
• B. 12
• C. 16
• D. 24Standardized & Admissions Tests

Explanation: Industrial battery capacity is commonly specified at the 8-hour discharge rate, written as an 8-hour or C8 rating.

• A. colour of electrode
• B. gassing
• C. specific gravity
• D. all above

Explanation: Near full charge, a battery shows electrolyte gassing, a stabilized or increased specific gravity, and characteristic electrode-colour…

• A. Deniell cell
• B. Leclanche cell
• C. Lead-acid cell
• D. Edison cell

Explanation: A dry cell is essentially a Leclanché cell in which the electrolyte is converted into a moist paste, making the cell portable and…

• A. produce gassing
• B. increase the internal resistance of the battery
• C. to corrode the positive plates into lead peroxide thereby weakening them physically
• D. bring about all above changes

Explanation: Overcharging decomposes water and causes gassing, raises internal resistance, and accelerates positive-plate corrosion and weakening.

• A. resistance of electrolyte
• B. electrode resistance
• C. surface contact resistance between electrode and electrolyte
• D. all above

Explanation: Cell internal resistance includes ionic resistance of the electrolyte, resistance of the electrodes, and contact or polarization…

• A. Capacity of cell will reduce
• B. Sulphation of plates will occur
• C. Internal resistance will increase
• D. All above will occur

Explanation: Deeply discharging a lead-acid cell promotes sulphation, reducing usable capacity and increasing internal resistance.

• A. low sp. gravity electrolyte
• B. abnormal high temperature
• C. reduced gassing on charge
• D. all above

Explanation: A short circuit rapidly discharges the cell, lowers electrolyte specific gravity, and produces abnormal heating.

• A. more when it is supplying current for intermittent periods
• B. more when it is supplying current for continuous periods
• C. unaffected by the type of discharge
• D. none of the above

Explanation: A dry cell generally delivers more effective capacity with intermittent discharge because rest periods allow electrochemical polarization…

• A. the loss of capacity of the cell
• B. the decrease of the specific gravity
• C. the low voltage of the cell on discharge
• D. all above conditions

Explanation: Sulphation reduces the amount of usable active material, causing lost capacity, reduced specific gravity and low discharge voltage.

• A. excessive gassing will occur
• B. temperature rise will occur
• C. bulging and buckling of plates will occur
• D. all above will occur

Explanation: Charging at an excessive rate produces heat and vigorous gassing, and the resulting thermal and mechanical stress can buckle or bulge the…

• A. Pb
• B. Pb02
• C. PbO
• D. PbS04

Explanation: In a lead-acid cell, both plates progressively form lead sulphate during discharge: lead dioxide at the positive plate and spongy lead at…

• A. ions
• B. holes
• C. electrons
• D. none of the above

Explanation: Electrolytes conduct through the movement of positively and negatively charged ions.

• A. current delivered by the battery will be high
• B. current drawing will be nil
• C. current drawing will be very small
• D. current drawing will be very high

Explanation: Reverse connection during charging makes the supply voltage oppose the battery emf, leaving mainly the small internal resistance to limit…