1. which statment is true?
- A. During the winter solstice, North America experiences its longest days
- A. During the winter solstice, North America experiences its longest days
- A. During the winter solstice, North America experiences its longest days
- A. During the winter solstice, North America experiences its longest days
correct
INTRODUCTION
CONTINUE TO ACTIVE FIGURE
INTRODUCTION
Humidity is a measure of how much water is held in air as water vapour. It can be measured in absolute terms as grams of water per cubic meter of air.
There are limits to how much water vapour air can hold. The limit changes with the temperature of the air. The higher the temperature, the more water vapour air can hold. The lower the temperature, the less water vapour air can hold.
The maximum amount of water vapour in air varies from around 5 grams per cubic meter (on the coldest winter day you’ll ever see) to about 65 grams per cubic meter (on the hottest day you’ll experience). That’s a lot of variation for the same one cubic meter of air!
Relative humidity is determined by dividing how much water is, in fact, in the air by how much water air at that temperature can possibly hold. It’s expressed as a percent. If the relative humidity is 50% you know that the air is holding half of the water vapour which it could, while a relative humidity of 100% means that the air is holding all the water vapour it possibly can at the current temperature.
Imagine a volume of air on a hot summer’s day that is at 35 degrees C and is holding 53 grams of water vapour per cubic meter of air. At those conditions, the air is at 100% relative humidity, meaning it is saturated with water vapour.
When the sun goes down the air is likely to cool. But at cooler temperatures, the air cannot hold as much water vapour. What happens? The water will condense, forming water droplets, or dew.
The dewpoint is the temperature at which water droplets will form for air with a given humidity.
The active figure shows the relationships among these different variables. As you look at it you can choose a temperature and humidity value by moving the gray box around with the pointer. Note that it’s the center of the gray box that shows the specific values. When you have explored the relationships involved, jot down the values for the following:
At a temperature of 30 degrees with water vapour of 20 grams per cubic meter of air, what is:
Relative humidity?
Dewpoint temperature?
Saturation vapour pressure?
Then proceed to the quiz questions to test your knowledge.
CREDITS
Brooks/cole
Ericka Yeomon-Saler, Technology Project Manager,
Chemistry and Earth scienceLiving Text LLC
Perry J.Samson, Project Director
Deborah M.Gibson, Interface Design
Brian Grimm, 3D Animation
Ian Tadashi Moore, Flash Animation