USCG Exam PracticeDC circuits and electronic principles
A lead-acid storage cell has a nominal open-circuit voltage of 2.1 V. A technician measures 2.1 V at the terminals with no load connected, but the terminal voltage drops sharply when a load is applied. What is the most likely cause?
- A. The cell's electrode chemistry has changed, lowering the EMF under load.
- ✓ The cell has high internal resistance, causing a large voltage drop equal to load current times internal resistance.Correct
- C. The cell is a primary type and is being discharged for the first time.
- D. The electrolyte concentration is too high, increasing the cell's amp-hour capacity.
Why B is correct
Terminal voltage under load equals open-circuit EMF minus the internal-resistance drop (I × r). A cell with high internal resistance produces a large drop under load even though its no-load voltage appears normal. This is a key diagnostic indicator described in NEETS Mod. 1 §2-1.
Cited:NEETS Mod. 1 §2-1