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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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When a lead-acid battery is in fully charged condition, the colour of its positive plate is
dark grey
brown
dark brown
none of the above
dark brown
In a fully charged lead-acid battery, the active material of the positive plate consists of Lead Peroxide (PbO2), which exhibits a characteristic dark brown color. The negative plate, composed of sponge lead (Pb), appears grey or slate grey.
In a fully charged lead-acid battery, the active material of the positive plate consists of Lead Peroxide (PbO2), which exhibits a characteristic dark brown color. The negative plate, composed of sponge lead (Pb), appears grey or slate grey.
PbSO4+2H2OchargePbO2+H2SO4+H2 — Positive plate charging reaction
During the charging process, the electrical energy induces a chemical reaction where lead sulfate (PbSO4) on the plates is converted. At the positive plate, PbSO4 reacts with the electrolyte and water to form Lead Peroxide (PbO2), which is dense and dark brown in color. The reaction is: PbSO4+2H2O+SO4°2−→PbO2+2H2SO4.
Positive plate is made of Lead Peroxide (PbO2).
Negative plate is made of Sponge Lead (Pb).
State of charge can be visually estimated by plate color.
Fully discharged plates appear white due to the accumulation of lead sulfate.
High surge current capability
Low self-discharge rate compared to other rechargeable chemistries
Low energy-to-weight ratio
Risk of sulfation if left in a discharged state
Automotive starting, lighting, and ignition systems
Uninterruptible Power Supplies (UPS)
As the battery discharges, the dark brown PbO2 is converted back to white PbSO4, causing the plate color to lighten.
Option A (Dark Grey) is incorrect as it typically describes the negative plate or a partially discharged positive plate.
C is correct — The positive plate of a fully charged lead-acid battery is dark brown because it consists of lead peroxide (PbO2).
Always remember: PbO2 (positive) is dark brown, Pb (negative) is grey, and PbSO4 (discharged/sulfated) is white/light grey.