Name:________________________________________________ Section:________________
Moisture Phase Changes and Measuring
Humidity
1. When water freezes, is heat released or absorbed by the ice?
2. How many calories would it take to evaporate 80 grams of water?
48,000
3. When ice melts, would you expect the temperature of the surrounding air to increase or decrease? DECREASE, UNLESS THE ICE IS CONCURRENTLY RECEIVING A COMMENSURATE AMOUNT OF HEAT FROM THE GROUND
4. Many environmental factors influence the rate of evaporation from an open water surface. List three factors that could be important.
a. AIR TEMPERATURE
b. WATER TEMPERATURE
c. HUMIDITY/CLOUD COVER (also WINDINESS, WATER AVAILABILITY)
5. If the amount of water vapor in the air stays constant, and the temperature of the air decreases, will the relative humidity increase, decrease, or stay the same?
6. If the amount of water vapor in the air increases, and the temperature of the air stays constant, will the vapor pressure increase, decrease, or stay the same?
INCREASE
7. If the amount of water vapor in the air stays constant, and the temperature of the air increases, will the specific humidity increase, decrease, or stay the same?
8. If the amount of water vapor in the air stays constant, and the temperature of the air decreases, will the saturation mixing ratio increase, decrease, or stay the same?
DECREASE
9. If the amount of water vapor in the air decreases and the temperature of the air stays constant, will the dew point temperature increase, decrease, or stay the same? DECREASE
10. Using a sling psychrometer, you measure an air temperature of 30°C and a wet-bulb temperature of 25°C.
a. What is the wet-bulb depression? 5OC
b. What is the dew point temperature? 23OC
c. What is the relative humidity of the air? 67%
11. Use a sling-psychrometer to calculate the dew point temperature and the relative humidity in the classroom.
a. What is the air temperature?
b. What is the wet-bulb temperature?
c. What is the wet-bulb depression?
d. What is the dew point temperature?
e. What is the relative humidity of the air?
Use Figure 5.2 to answer the following questions.
12. If the air temperature is 25°C, what is the maximum amount of water vapor that the air can hold? 20.5 G/KG
13. If the air temperature is 5°C, what is the maximum amount of water vapor that the air can hold? 6.5 G/KG
14. If the air temperature increases from 25°C to 35°C, how much more water vapor can the air hold? ~18 GM/KG MORE
[37.5gm/Kg @ 35OC] - [ 20.5gm/Kg @ 25OC]
15. If the air temperature increases from 5°C to 10°C, how much more water vapor can the air hold? ~2 GM/KG MORE
[6.5 gm/Kg @ 5OC] - [8.5 gm/Kg @ 10OC]
16. If the water vapor content of the air is 12 g/kg, and the air temperature is 30°C, what two specific actions will make the air saturated?
a. ADD 16 G/KG MORE WATER VAPOR (I.E., RAISE THE HUMIDITY CONTENT)
b. COOL THE TEMPERATURE TO 15OC (I.E., REMOVE HEAT ENERGY TO REDUCE CAPACITY)
17. If the water vapor content of the air is 8 g/kg, and the air temperature is 30°C, what is the relative humidity? 28.6%
30OC=28 gm/Kg
100(8/28)=28.6
18. If the relative humidity of the air is 60%, and the temperature of the air is 10°C, how much water vapor is present in the air? 5.1GM/KG
10OC=8.5gm/Kg 8.5(.6)=5.1
19. Cold, continental polar air is often described
as being dry even when its relative humidity is very high. Why is this so? IT HAS VERY LOW SPECIFIC HUMIDITY, BUT VERY
LOW TEMPERATURE (THUS MOISTURE CAPACITY) MEANS THAT THE AIR WITH SO SMALL A
MOISTURE CONTENT IS STILL NEARLY AT
20. A snowstorm is occurring in
a. Which location has
the highest relative humidity? CHICAGO
DEW POINT = DRY BULB (AIR) TEMPERATURE (3.5 G/KG)
b. Which location has the highest vapor pressure? ATACAMA DESERT
ATACAMA DEW POINT > STEVENS POINT'S DEW POINT (8.0 G/KG)