Humidity is measured by difference between which two thermometers?

• A. Wet Bulb and Dry Bulb Thermometers
• B. Maximum and Minimum Thermometers
• C. Wet Bulb and Hygrometer
• D. Dry Bulb and Barometer

Answer: (A)

Humidity is determined from the readings of two thermometers: a dry-bulb thermometer that measures the air temperature and a wet-bulb thermometer whose bulb is wrapped in a water-soaked wick. As air moves past the wick, water evaporates and cools the wet-bulb thermometer. The amount of cooling depends on how much moisture is already in the air—the drier the air, the more the wet-bulb cools, so the bigger the difference between the two readings; in more humid air, evaporation slows and the two temperatures are closer. This difference, the wet-bulb depression, is used to calculate humidity (often via a psychrometric chart). That’s why the measure of humidity relies on the difference between wet-bulb and dry-bulb thermometers. Other pairings don’t directly give humidity in this standard method: maximum and minimum track daily extremes, a wet-bulb with a hygrometer isn’t the classic two-thermometer setup, and a dry-bulb with a barometer combines temperature and pressure, not humidity.