Dew point — Science definition
Defined in 2 courses:
- Temperature at which cooling air reaches saturation under the specified conditions. (Physical Science: Matter, Forces & Energy)
- The temperature associated with saturation for the moisture present under the stated pressure conditions. (Earth & Space Science)
Where it is taught
- Evaporation, Condensation & a Wet Cold Cup — Phases of Matter, Physical Science: Matter, Forces & Energy, Grade 8
- Reading Weather Patterns — Atmosphere & Weather, Earth & Space Science, Grade 9
Questions using dew point
Problem 1
Air dew point is supplied as 15 °C. An intact cup surface is 18 °C and another is 9 °C. Predict the condensation comparison and account for water origin.
Hints
Distinguish the observed quantities, the proposed mechanism and its conditions.
Answer and explanation
The 9 °C surface is below the dew point and more likely to collect droplets; the 18 °C surface is above it. Existing water vapor from air can supply the condensate. The prediction uses the stated air conditions.
The 9 °C surface is below the dew point and more likely to collect droplets; the 18 °C surface is above it. Existing water vapor from air can supply the condensate. The prediction uses the stated air conditions.
Problem 2
A station reports 18 °C with a dew point of 18 °C. What is the relative humidity, as a percentage?
Answer and explanation
100 %
When temperature equals dew point the air is saturated, so relative humidity is 100 percent.
Problem 3
Dew point is the temperature at which air
- freezes
- becomes saturated and condensation begins
- boils
- stops moving
Answer and explanation
becomes saturated and condensation begins
A dew point close to the air temperature indicates humid air and likely fog or cloud.
Taught alongside
- evaporation
- condensation
- water vapor
- humidity
- model
- evidence
- system boundary
- assumption
- isobar
- station model
- meteorologist
- prevailing westerlies
- relative humidity