Mammatus clouds
Date Time(cdt)
Wind(mph) Weather Sky Cond.
Temperature (ºF)
RelativeHumidityAir Dwpt
07 06:55 E 8 Fair CLR 39 32 76%
07 06:35 NE 3 Fair CLR 37 31 80%
07 06:15 NE 6 Fair CLR 38 32 77%
07 05:55 E 7 Fair CLR 38 32 80%
07 05:35 E 5 Fair CLR 37 32 83%
07 05:15 NE 6 Fair CLR 36 32 84%
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/kgRelative 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