The capacity of a lead-acid cell does not depend on its

Question

Examoogle · Accepted Answer

rate of charge

Explanation: The capacity of a lead-acid battery is defined as the total amount of charge (in Ampere-hours) it can deliver until it reaches a specified cutoff voltage. While capacity depends on discharge rate (Peukert's Law), temperature, and active material quantity, the rate at which the battery is charged does not inherently determine its total capacity.

Working Principle: Battery capacity is essentially limited by the surface area of the plates and the availability of active material ($Pb$ and $PbO_2$) involved in the electrochemical reaction. As the discharge rate increases, the effective capacity decreases because the chemical reaction cannot keep pace with the current demand. Charging rate only determines the time taken to reach a full state of charge, not the storage volume itself.

Key Formulas: $C = I 	imes t$; $C_p = I^k 	imes t$ — Peukert's law describing capacity variation with discharge rate

Key Points: Capacity is expressed in Ampere-hours (Ah).; High discharge rates lead to lower effective capacity due to diffusion limitations of the electrolyte.; Higher temperatures typically increase capacity by improving electrolyte diffusion and chemical reaction kinetics.; Increasing the quantity of active material (plates/acid) directly increases the ampere-hour rating.

Advantages: Predictable behavior under standard conditions; High efficiency at low discharge rates

Disadvantages: Sensitivity to ambient temperature variations; Non-linear capacity drop at high loads

Applications: Automotive starting systems; Uninterruptible Power Supplies (UPS); Solar power storage

Additional Info: The rate of charge affects the charging efficiency and the safety of the battery, but it does not define the capacity storage.. Option B is the correct answer because charging rate is an input parameter for the replenishment process, whereas capacity is an inherent capability of the chemical structure.

Answer: B is correct — The charging rate determines how fast energy is replenished, but it does not dictate the total energy storage capacity of the lead-acid cell.

Exam Tip: Remember that capacity is a measure of potential storage, whereas charging rate is a measure of input velocity; they are independent variables in battery management.

Related Questions

Discussion (0)