What type of thermometer reads the dew point of the air?

• A. Wet bulb
• B. Dry bulb
• C. Mercury thermometer
• D. Digital thermometer

Answer: (A)

Dew point is found by looking at how humidity affects temperature readings, usually through a two-thermometer setup. A psychrometer uses a dry-bulb thermometer to measure the ambient air temperature and a wet-bulb thermometer, where the bulb is moistened. As air passes over the wet wick, evaporation cools the bulb. The amount of cooling depends on how much moisture is in the air: the drier the air, the more cooling; the more humid, the less cooling. By comparing the dry-bulb and wet-bulb readings (or using a psychrometric chart), you can determine humidity and derive the dew point. So, the wet-bulb thermometer is the one that provides the information needed to read the dew point in this context. A mercury thermometer or a digital thermometer simply measures ambient temperature and does not directly give the dew point.