# Relative Humidity Geology Lab-The University of Texas at Arlington.

5:32 14 < Back 1401 Lab Manual.pdf Q ♡ 3. To better illustrate the relationship between the Saturation Mixing Ratio and temperature, create a graph using Figure 1 by plotting the data provided in Table 1 above. 4. Based on your graph (Figure 1) and Table 1, briefly explain the relationship between the amount of water vapor needed for saturation and temperature. 117 Part 2: Relative Humidity and Dew Point Background: The most common measurement used to describe the amount of water vapor in the air is known as Relative Humidity. It describes how close the air is to being saturated and is given as percentage. Below is the formula for calculating the relative humidity: Water Vapor Content Relative Humidity (%)= x 100 Saturation Mixing Ratio Example from Table 1: The saturation mixing ratio of air at 15°C is 10 g/kg. If the actual water vapor in the air was 2 g/kg, the relative humidity of the air would be calculated as: 2 g/kg Relative Humidity (%)= 10 g/kg X 100 Relative Humidity (%)= 20% 5. Use Table 1 and the formula to calculate relative humidity for the following examples. Notice the temperature is the same and the water vapor content varies for all the examples. Air Temperature (°C) Water Vapor Content (g/kg) Relative Humidity (%) 15 2 15 5 15 7 6. Use the information from #5 above to answer the following questions: a. Adding water vapor will increase / decrease ) relative humidity b. Reducing water vapor will ( increase / decrease ) relative humidity 7. Again, use Table 1 and the formula to calculate relative humidity for the following examples. Notice the temperature varies and the water vapor content remains the same for all the examples. Air Temperature (°C) Water Vapor Content (g/kg) Relative Humidity (%) 25 5 15 5 5 5 a. 8. Use the information from #7 above to answer the following questions: When the water vapor content remains the same, cooling the air ( raises / lowers ) the relative humidity. b. When the water vapor content remains the same, increasing the air temperature ( raises / lowers ) the relative humidity. (continued on next page) 118 < Previous Next → 8 Dashboard Calendar To Do Notifications Inbox 5:32 14 < Back 1401 Lab Manual.pdf Q a. When the water vapor content remains the same, cooling the air (raises / lowers ) the relative humidity. b. When the water vapor content remains the same, increasing the air temperature ( raises / lowers ) the relative humidity. (continued on next page) 118 Think About It…. 9. When we heat our homes in the winter, what effect does the heating have on the relative humidity inside the home? What can be done to lessen this effect? Misconception… When you hear that the relative humidity on a cold, winter day is 90% and then hear that the relative humidity on a hot, summer day is 40%, you conclude that the cold, winter day contains more water vapor in the air than on the hot, summer day. Right? Wrong! Complete the following questions to understand why relative humidity can be misleading 10. Use Table 1 and the equation for finding relative humidity to calculate the water vapor content for the two examples below: SUMMER Air Temperature = 77°F Relative Humidity = 40% Water Vapor Content = WINTER Air Temperature = 41°F Relative Humidity = 90% Water Vapor Content = g/kg g/kg 11. Explain why relative humidity does NOT give an accurate indication of the actual amount of water vapor in the air. Dew Point Background: Dew Point is the temperature at which saturation occurs, or in other words, it is the temperature when the relative humidity of the air is 100%. Example from #7: In the table you completed for #7, you determined that air at 25°C, containing 5 g of water vapor, had a relative humidity of 25%. This indicates the air is NOT saturated. However, when the temperature dropped to 5°C, the air had a relative humidity of 100% and IS saturated. Thus, the 5°C is the dew-point temperature for that example. 12. Use Table 1, determine the dew point temperature for air that contains 7 g of water vapor content at saturation? °C 13. What are the relative humidity and dew point temperature of air that is 25°C and contains 10 g of water vapor? a. Relative Humidity = % b. Dew Point Temperature = °C 119 < Previous Next → 8 Dashboard Calendar To Do Notifications Inbox 5:32 14 < Back 1401 Lab Manual.pdf Q Ø 119 Part 3: Measuring Relative Humidity & Dew Point N. Background: A Sling Psychrometer is one method used to determine relative humidity and dew point temperature of the air. A sling psychrometer consists of two identical thermometers attached side-by-side. One thermometer measures the air temperature and is called the dry-bulb thermometer. The second thermometer, called the wet- bulb thermometer, has a wet cloth wrapped around its bulb. As the thermometers are spun for about 1-2 minutes, water on the wet-bulb evaporates and cooling results. In dry air, the rate of evaporation will be higher than in humid air. After recording the temperatures from both thermometers, you can use the following two tables (Tables 2 and 3) to determine relative humidity and dew point. 14. Use Table 2 to determine the relative humidity for each of the following results from the psychrometer: READING 1 20°C 18°C C % READING 2 32°C 25°C Dry-bulb temperature Wet-bulb temperature Difference between dry- and wet-bulb temperatures Relative Humidity °C % 15. Based on the results from the previous question, describe the relationship between the difference in the dry-bulb and wet-bulb temperatures compared to the relative humidity of the air. 16. Use Table 3 to determine the dew point temperatures for each of the following results from the psychrometer: Dry-bulb temperature Wet-bulb temperature Difference between dry- and wet-bulb temperatures Dew Point Temperature READING 1 8°C 6°C C READING 2 30°C 24°C °C C C 17. Use the sling psychrometer to determine the relative humidity and dew point temperature of the air in your classroom and outside the building. ROOM OUTSIDE С “С °C Dry-bulb temperature Wet-bulb temperature Difference between dry- and wet-bulb temperatures Relative Humidity Dew Point Temperature C °C °C % % °C C 120 DRY-BULB DEPRESSION OF WET-BULB TEMPERATURE (°C) < Previous Next → 8 Dashboard Calendar To Do Notifications Inbox