Physical Geography Laboratory Manual Name Section EXERCISE 20 PROBLEMS-PART I (S
ID: 153432 • Letter: P
Question
Physical Geography Laboratory Manual Name Section EXERCISE 20 PROBLEMS-PART I (S.I. Units) Using the psychrometer tables (Figures 20-2 and 20-3) and the table of saturation mixing ratios Figure 20-1), answer the following questions about determining relative humidity with a sling psychrometer. 1. If the dry-bulb temperature is 32°C, and the wet-bulb temperature is 26°C (a) (b) (c) What is the relative humidity? What is the dew point? What is the mixing ratio? (Estimate from Figure 20-1) oc g/kg If the dry-bulb temperature is 14°C, and the wet-bulb temperature is 12°C (a) (b) (c) 2. What is the relative humidity? What is the dew point? What is the mixing ratio? (Estimate from Figure 20-1) oC gkgExplanation / Answer
1. a. The relative humidity is 63%.
(First Subtract the wet-bulb temperature from the dry-bulb temperature. Find this number—the difference in degrees—at the top of the chart and place your finger on it. Find the dry-bulb temperature in the first column on the left. Place your finger on it. Bring your fingers down the column and across the row. The relative humidity percentage appears where column and row intersect on the chart).
b. The dew point temperature is 24.1° C
c. The mixing ratio is 30.02 g/kg
2. a. The relative humidity is 80%.
b. The dew point temperature is 10.6° C
c. The mixing ratio is 12.78 g/kg
The amount of moisture air can hold is dependent on its temperature and pressure. The warmer the air the greater the quantity of water vapour it can contain. The air temperature is measured with a normal thermometer this is the Dry-Bulb reading. The actual amount of moisture known as the mixing ratio is measured in grams of water per kilogram of dry air. When air at a certain temperature is saturated it cannot hold any more moisture. The relative humidity of the air is the ratio of the actual amount of moisture in the air to the saturated amount.
If partly saturated air is cooled without changing its pressure or amount of water vapour, a point is reached when it becomes saturated. The moisture will be given up as dew or ice crystals. This temperature is the Dew Point.