Psychrometer (61 Near Nature Experiments)

You will need:

1. Large thick rectangular piece of cardboard
2. Piece of cottonq
3. Warm water
4. Rubber band
5. Table fan
6. Tape
7. 2 alcohol therm

Note the increase or decrease in humidity levels with your very own psychrometer.

INSTRUCTIONS

1. Take your cardboard, and holding it
   vertically, attach the thermometers to the cardboard with tape.
2. Make sure the bulbs of the thermometers extend below the cardboard.
3. Mark the different temperature readings from the thermometers clearly on the cardboard.
4. Fix the cardboard on a wall and place a table
   fan in front of it. Set the fan at normal speed for
   5 minutes and record the temperature readings
   on both the thermometers.
5. Wet a piece of cotton in warm water and
   secure it around the bulb of only one of the
   thermometers using rubber band.
6. Set the fan at normal speed. Record the
   temperatures in both the thermometers after 5
   minutes.
7. To get the humidity level, subtract the
   temperature of the cotton-covered thermometer
   from that of the normal thermometer.

RESULT

The temperature of the cotton-covered thermometer will be lower than that of the other thermometer. This is because water evaporates from the wet cotton, taking up a bit of heat from the surroundings, thus reducing the temperature of the cotton-covered needle.