Which statement best describes the operating principle in a nickel-cadmium battery installed in an aircraft?

Which statement best describes the operating principle in a nickel-cadmium battery installed in an aircraft?

• A. At full charge, the electrolyte will be at its lowest level and should be filled
• B. When positive plates slowly give up oxygen, which is regained by the negative plates, the battery is charging
• C. To completely charge a nickel-cadmium battery, some gassing must take place; thus, some water will be used
• D. Some oxygen is produced at the negative plate during charging

Answer: (C)

Charging a nickel‑cadmium cell involves a small amount of gas generation. When the cell is charged, the water in the potassium hydroxide electrolyte is split through electrolysis, producing oxygen at the positive electrode and hydrogen at the negative electrode. This gas evolution means some electrolyte (water) is consumed to complete the chemical reactions, so to reach a full charge a bit of gassing must occur. That makes the statement about some gassing and water use during full charging the best description. The other ideas don’t fit the chemistry: during charging, gas is produced at the positive plate (not the negative), and simply thinking in terms of electrolyte level being low isn’t a reliable or complete description of the charging process.

Charging a nickel‑cadmium cell involves a small amount of gas generation. When the cell is charged, the water in the potassium hydroxide electrolyte is split through electrolysis, producing oxygen at the positive electrode and hydrogen at the negative electrode. This gas evolution means some electrolyte (water) is consumed to complete the chemical reactions, so to reach a full charge a bit of gassing must occur. That makes the statement about some gassing and water use during full charging the best description.

The other ideas don’t fit the chemistry: during charging, gas is produced at the positive plate (not the negative), and simply thinking in terms of electrolyte level being low isn’t a reliable or complete description of the charging process.