Which device is commonly used to measure the specific gravity (density relative to water) of a liquid in a cell, such as in a lead-acid battery?

• A. Spectrophotometer
• B. Barometer
• C. Hydrometer
• D. Manometer

Answer: (C)

Verified step by step guidance

1. Understand that specific gravity is the ratio of the density of a liquid to the density of water at a reference temperature, usually 4°C.
2. Recall that to measure specific gravity directly, a device must be able to compare the density of the liquid to that of water without complex calculations.
3. Identify that a hydrometer is a device designed to float in the liquid, and the level to which it sinks correlates with the liquid's density relative to water.
4. Recognize that other devices listed, such as a spectrophotometer, barometer, and manometer, measure different properties: spectrophotometer measures light absorbance, barometer measures atmospheric pressure, and manometer measures pressure differences.
5. Conclude that the hydrometer is the appropriate and commonly used device to measure specific gravity in liquids like the electrolyte in a lead-acid battery.