Dew Point: What is the dew point?

Dew Point: What is the dew point?

• A. The temperature at which moisture will condense out of air.
• B. The temperature at which air becomes completely dry.
• C. The point at which air humidity peaks.
• D. The temperature at which air holds its maximum vapor.

Answer: (A)

Dew point is the temperature to which air must be cooled (at constant pressure) for water vapor to begin condensing into liquid. When air is cooled to this temperature, it reaches 100% relative humidity, and moisture will start to condense on surfaces as dew, fog, or condensation. This makes sense because warmer air can hold more water vapor, and cooling it down reduces that capacity until saturation occurs at the dew point. The other ideas aren’t correct because drying the air isn’t what dew point measures, and humidity doesn’t have a single peak value. Humidity is a percentage of saturation that changes with temperature, so it isn’t defined by a fixed “peak” or by the air’s maximum vapor capacity independent of temperature.

Dew point is the temperature to which air must be cooled (at constant pressure) for water vapor to begin condensing into liquid. When air is cooled to this temperature, it reaches 100% relative humidity, and moisture will start to condense on surfaces as dew, fog, or condensation. This makes sense because warmer air can hold more water vapor, and cooling it down reduces that capacity until saturation occurs at the dew point.

The other ideas aren’t correct because drying the air isn’t what dew point measures, and humidity doesn’t have a single peak value. Humidity is a percentage of saturation that changes with temperature, so it isn’t defined by a fixed “peak” or by the air’s maximum vapor capacity independent of temperature.