Relative Humidity and Dewpoint Temperatures

Name ______

RELATIVE HUMIDITY AND DEWPOINT TEMPERATURES

Introduction: The capacity of air for holding water vapor depends on the temperature of the air. As the air temperature increases the molecules move______. Therefore, warm air can hold more water vapor due to the space between molecules. The molecules for cold air are ______and therefore not much room is available for water molecules. Therefore as temperature increases, the air’s ability to hold water ______.

Relative Humidity is the relationship between the amount of water in the air compared to its capacity to hold water at a given temperature (this is given in %)

Ai is said to be saturated when ______. The temperature at which saturation occurs is called the dew point temperature.

Objective: In this lab you will learn how to determine relative humidity and dew pint using the charts in the ESRT’s.

Vocabulary

Relative Humidity-

Dew Point-

Sling Psychromotor-

Condensation-

Evaporation-

Procedure 1.

Using the sling psychrometer readings from the student out the window, write down the dry bulb temperature and wet bulb temp’s in °C. Use these numbers and the ESRT to determine the dew point temperature and the relative humidity. Then find the % error between our measured dew pint temperature and the actual dew pint temperature given by Weather.com.

Dry Bulb ____ °F = ____°C Wet Bulb ____°F = ____°C

Measured Dew Point Temp ____°C Relative Humidity ____ %

Accepted Dew Point from Weather.com ____°C Calculated % Error ______

(% ERROR = Measure Value- Accepted Value) x 100%

Accepted Value

Procedure 2: Refer to the ESRT’s to determine the dew point. An example is provided for you.

Example: Find the dew point if the dry bulb temperature is 12°C in the dry bulb column, SUBTRACT (12-8) and get 4, this is your difference between wet bulb and dry bulb. Then use the chart to see where the 12°C and the 4° difference meet. This gives your dew point temperature of 4°C.

Find the dew point if the dry- bulb temp. is – 16 °C and the wet bulb is -15°C? ______

Find the dew point if the dry- bulb temp. is 16 °C and the wet bulb is 5°C? ______

Find the dew point if the dry- bulb temp. is 5 °C and the wet bulb is 3°C? ______

Find the dew point if the dry- bulb temp. is 14°C and the wet bulb is 10°C? ______

Find the Wet Bulb if the Dry bulb temp. is 20°C and the Dew Point is 12°C?______

Find the Wet Bulb if the Dry bulb temp. is 8°C and the Dew Point is -5°C?______

Find the dew point if the dry- bulb temp. is 4 °C and the wet bulb is 1°C? ______

Procedure 3- Use the ESRT’s to find the Relative Humidity

What is the relative humidity if the dry bulb is 12°C and the wet bulb is 7°C?______

What is the relative humidity if the dry bulb is 2°C and the wet bulb is 0°C?______

What is the relative humidity if the dry bulb is 20°C and the wet bulb is 20°C?______

What is the relative humidity if the dry bulb is 15°C and the wet bulb is 12°C?______

What is the wet bulb temperature if the dry bulb is 8 °C and the relative humidity is 39%? _____

What is the wet bulb temperature if the dry bulb is 24 °C and the relative humidity is 42%? ____

What is the relative humidity if the dry bulb is 2°C and the wet bulb is -8°C?___ ( think & look!)

Challenge! Extra Credit (do not ask questions, because I will not help you)

What is the dew point temperature if dry bulb is 12°C and relative humidity is 57%? ______

What is the relative humidity when the dry bulb is 11°C and the dew point is 5°C? _____

Questions:

1. How does the relative humidity change as the difference between the wet bulb temperature and the dry bulb temperature increases?

2. If the dry bulb temperature and the dew point temperature are equal, describe the weather that exists?

3. How does the amount of moisture in the air change as the difference between the dew point temperature and the dry bulb temperature decreases?

4. How does the temperature of the air change as you increase in altitude in the troposphere?

5. How does the air’s capacity to hold water change as elevation increases?

6. As a give parcel of air is cooled and the amount of moisture (gallons) in the air remains the same, how will the relative humidity change?

7. Why can warm air hold more water vapor than cold air?

For each of the following write down either dry or wet. Use the ESRT and your BRAIN (think!)

8. Temp 20°C, Dew Pt. 19°C ______10. Temp 15°C, Dew Pt. 6°C______

9. Temp 5°C, Dew Pt. 4°C ______11. Temp 26°C, Dew pt. 9°C______

Conclusion: How are relative humidity and dew point determined using a sling psychrometer?

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