Mammatus clouds

DateTime (cdt) Wind (mph) WeatherSky Cond. Temperature (ºF) Relative Humidity AirDwpt 0706:55E 8FairCLR393276% 0706:35NE 3FairCLR373180% 0706:15NE 6FairCLR383277% 0705:55E 7FairCLR383280% 0705:35E 5FairCLR373283% 0705:15NE 6FairCLR363284%

Ch 18 Measuring Humidity Lab Problem: How can relative humidity be determined? You will be able to calculate the humidity of the air using data and a hygrometer.

Ch 18 Lab Relative humidity is a measurement used to describe water vapor in the air. In general, it expresses how close the air is to saturation. In this lab, you will use a psychrometer and a data table to determine the relative humidity of air.

25˚C = 20 g/kg Relative Humidity (%) = 5 ÷ 20 =.25 RH =.25 x 100 = 25%

Part B: Determining Relative Humidity Using a Psychrometer A psychrometer consists of two thermometers—a wet- bulb thermometer and a dry-bulb thermometer. The wet-bulb thermometer has a cloth wick that is wet with water and spun for about 1 minute. Relative humidity is determined by calculating the difference in the temperature reading between the dry- bulb temperature and the wet-bulb temperature and using Data Table 2. Wet-bulb Dry-bulb

4) Suppose a dry-bulb temperature is measured as 20°C, and a wet-bulb temperature is 14°C. Read the relative humidity from Data Table 2. Write it down.

5) Make wet-bulb and dry-bulb temperature measurements for the air in your classroom and the air outside. – Dry-bulb = plain thermometer – Wet-bulb = wet cloth thermometer in front of fan (2 min). Use Data Table 3 to record your measurements. Use your measurements and Data Table 2 to determine the relative humidity inside and outside. Wet-bulb Dry-bulb