Name_____________________________________________Date__________________Per.______
Relative Humidity and Dew Point Lab
Background Review:
1.
What happens to the amount of water vapor that can be present in air as it warms up?
2. Air conditioners are always vented to the outside because water condensation usually forms.
Explain why this usually occurs and what would affect whether condensation forms.
3.
The dew point is the temperature at which condensation will form as air cools. If air contains 18
g/cubic meter water vapor, what is its dew point?
4.
Relative humidity is the amount of water vapor in the air compared to the maximum amount of
water vapor that can be “held” in the air at that given temperature. The formula to calculate
relative humidity is:
Relative Humidity (%) = (Actual Water Vapor Density ÷ Maximum Water Vapor Density) x 100
Calculate the relative humidity for air that contains 9 g/cubic meter water vapor at the
temperatures given below. In order to calculate the relative humidity, use the graph to determine
the maximum water vapor density (saturation quantity). Show your work.
A. 10 °C
B.
40 °C
5.
Explain how temperature relates to relative humidity for a given water vapor density as the
temperature increases.
6.
On a September day the temperature in Seattle is 20oC and the relative humidity is 60%. The air in
Seattle travels west and is forced to rise when it reaches the Cascade Mountains. As it rises, it cools.
A.
Use the graph determine the maximum water vapor content of20oC air and then calculate
the actual water vapor content of the 60% humidity air using the relative humidity formula
from the previous page. Show your work.
B. Use the graph to determine at what temperature the air will become saturated and clouds
will form as the air cools.
7. The air at Snoqualmie pass is 5oC (41oF) and has a relative humidity of 80%. As the air descends into
Eastern Washington, it warms up to 25oC (77oF).
A.
Using the graph, calculate the actual water vapor content at 5oC. Show your work.
B.
Using the chart and the relative humidity equation, calculate what the relative humidity
will be in Eastern Washington when the air warms up to 25oC. Show your work.
8. Explain why the weather in Eastern Washington will have less precipitation than Western
Washington, and why the humidity will generally be lower in Eastern Washington than in Western
Washington.