Which of the following instruments may be used to measure relative humidity?

Analysis

The question asks for the specific scientific instrument used to determine the amount of water vapor present in the air, known as relative humidity.

Concept Explanation

To identify the correct instrument, we must distinguish between the functions of the devices listed:

• Hydrometer: This is used to measure the relative density (or specific gravity) of liquids. It works on the principle of buoyancy.
• Manometer: This is a device used to measure gas or liquid pressure. It typically consists of a U-shaped tube containing a liquid.
• Hygrometer: This is the standard instrument used to measure the humidity of the air. Common types include the hair hygrometer and the wet-and-dry bulb hygrometer (psychrometer).
• Hypsometer: This is used to calibrate thermometers or determine altitude by measuring the boiling point of a liquid at different pressures.

Step-by-Step Solution

1. Evaluate Option A: A hydrometer measures liquid density, not humidity. Incorrect.
2. Evaluate Option B: A manometer measures pressure, not humidity. Incorrect.
3. Evaluate Option C: A hygrometer is specifically designed to measure the moisture content (humidity) in the atmosphere. Correct.
4. Evaluate Option D: A hypsometer measures boiling points to determine altitude. Incorrect.

Exam Tip

Don't let the similar-sounding names confuse you! Remember:

• Hydro = Water/Liquid density (Hydrometer)
• Hygro = Humidity (Hygrometer)
• Hypso = Height/Altitude (Hypsometer)