What instrument measures air moisture content?

• A. Wet bulb
• B. Hygrometer
• C. Thermometer
• D. Anemometer

Answer: (A)

Measuring how moist the air is can be done by using evaporation to gauge humidity. A wet-bulb thermometer has its bulb wrapped in a water-soaked wick. As air moves over it, water evaporates and cools the bulb; the extent of cooling depends on how much moisture is already in the air. In dry air, evaporation is strong and the wet-bulb temperature drops noticeably; in moist air, evaporation slows and the wet-bulb temperature stays closer to the actual air temperature measured by a dry-bulb thermometer. By comparing the wet-bulb reading with the dry-bulb reading (and using a psychrometric chart or calculations), you can determine the air’s humidity or moisture content. This makes the wet-bulb the instrument designed to measure air moisture content via evaporative cooling.