Key Idea: The amount of water vapor in the air at any place depends on the amount of liquid water available on the surface of the earth at that place, the temperature of the air, and where the air moved from.
Students are expected to know that:
- When liquid water at the surface of the earth (e.g., from rivers, streams, lakes, oceans, or living things) evaporates, the molecules of water become part of the air as water vapor.
- At any temperature there is a maximum number of molecules of water vapor that can be in a given quantity of air. As long as liquid water is available, the humidity of air can increase until it reaches this maximum.
- The maximum amount of water vapor that can be in air increases as the temperature of the air increases, so warm air can have more water vapor in it than cooler air.
- Because air can move water vapor from one location to another, areas that are not adjacent to a source of water can still experience humid air at times, but all other factors being equal, air in contact with or near bodies of water usually has more water vapor in it than air that is above dry land or is farther from a large body of water.
Boundaries:
- Students are not expected to know what relative humidity is or the difference between relative and absolute humidity.
- Students are not expected to know the term “dew point."
| Item ID Number |
Knowledge Being Assessed | Grades 6–8 |
Grades 9–12 |
Select This Item for My Item Bank |
|---|---|---|---|---|
52% |
59% |
|
||
Water vapor in air can come from water in plants and in the soil. | 41% |
46% |
|
|
As water evaporates from a lake, it becomes a gas that spreads throughout the air. | 40% |
46% |
|
|
40% |
45% |
|
||
35% |
43% |
|
||
Liquid water evaporates into the air both when the air is very cool and when the air is very warm. | 27% |
28% |
|
|
25% |
21% |
|
||
21% |
23% |
|
Misconception |
Student Misconception |
Grades |
Grades |
|---|---|---|---|
Water evaporates into the air only when the air is very warm (AAAS Project 2061, n.d.). | 48% |
47% | |
43% |
49% | ||
38% |
34% | ||
32% |
35% | ||
31% |
32% | ||
21% |
21% | ||
Cooler air can hold more water vapor than warmer air (AAAS Project 2061, n.d.). | 22% |
17% | |
20% |
16% | ||
Water evaporates into the air only when the air is very cool (AAAS Project 2061, n.d.). | 17% |
17% | |
16% |
11% | ||
Liquid water does not evaporate and become part of the air (AAAS Project 2061, n.d.). | 8% |
7% |
Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.