The dew point is read by which thermometer?

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

Answer: (C)

Dew point is the temperature at which air becomes saturated and water vapor begins to condense. To read it directly you need the temperature at which condensation starts on a cooled surface. In many dew-point instruments, a mercury thermometer is used to read that exact temperature, since it shows the surface temperature when condensation forms. Wet-bulb and dry-bulb readings are related to humidity calculations and can be used to derive dew point, but they don’t give the dew point directly. A thermocouple is just a temperature sensor and isn’t the readout method used for dew point in this context.