Activities

1998 WWLPT Environmental Institute: Humidity

Activities Return to Humidity Homepage

Activity 1: Invisible Water Vapor

    Materials:
                                Tea Kettle
                      Candle
                                 Hot Plate
                      Cigar

    Procedure:
                        1. Bring some water to a boil in a tea kettle. (White steam emerges at a distance from the nozzle.)
                        2. Hold a lighted candle in the cloud of condensed steam. (The cloud disappears.)
                        3. Introduce cigar smoke to the invisible portion of the steam.
(Clouds will form more readily.)

Explanation: Water vapor is invisible and cannot be seen near the nozzle. At a distance from the nozzle the vapor cools and condenses in the form of a white cloud. The cloud consists of small droplets of water and therefore is invisible. Heat from a candle is used to evaporate droplets. The cigar smoke provides particles on which condensation occurs.

Activity 2: Hair Hygrometer Return to Humidity Homepage

    Materials:
                    A few human hairs about 30 cm long
                    Stand
                    Spool
                    Broom straw
                    Nail
                    Piece of tin
                    Cardboard
                    50 g weight

    Procedure:
                      1. Wash the hairs in a shampoo solution and set aside to dry.
                      2. Attach one hair to the upper end of a stand and stretch it with a 50 g weight.
                      3. Wind the hair two or three times around a spool (or a 1 cm long soda straw) attached to an axle (a long nail). The axle should be able to rotate in bearings made from a piece of tin and fastened to the stand.
                      4. Fix a light pointer (a broom straw) to the axle and arrange a piece of cardboard as a scale.
                      5. As moisture in the air varies, the hair will change length.

Explanation: Hair tends to stretch as it absorbs moisture, and shrinks as it dries out. Blond hair is more sensitive to humid conditions and therefore works better. To calibrate, place the instrument above some warm water in a bucket and cover with a wet towel. When the pointer has moved as far as it will go, mark this point as 100% on the scale.

Activity 3: Wet-Dry Bulb Hygrometer Return to Humidity Homepage

    Materials:
                    Two inexpensive thermometers
                    White wick made of linen cloth
                    Small bottle

    Procedures:
                        1. Examine two thermometers by comparing their readings in different temperatures. If both agree, attach them to a piece of board, about 10 cm apart.
                        2. Place a small bottle just under the right hand side thermometer.
                        3. Fasten a white wick made of linen cloth around the exposed bulb, and dip it into the bottle.
                        4. Take the readings from both thermometers.
                        5. Generally, in a relative humidity table the temperature of the dry thermometer shows in the first column. The difference in the readings of both thermometers is shown in the top row. Numbers in the table indicate the relative humidity.

Activity 4: Evaporation Return to Humidity Homepage

Materials:
Container with water

    Procedure:
                    1. Dip the palm of one hand in the water, and keep the other one dry.
                    2. Notice that the wet palm feels cool.
                    3. Blow some air over the wet palm and notice that it feels even cooler.

Explanation: Perspiration cools the human body. During very humid weather, when relative humidity is near 100% perspiration evaporates too slowly to cool the body. As a result, one feels hot, sticky, and uncomfortable.

Activity 5: Deposition Return to Humidity Homepage

    Materials:
                    A large tin can
                    Thermometer
                    Ice
                    Salt
                    Stick

    Procedure:
                    1. Pack the can with alternate layers of ice and salt. Poke the mixture with a stick while you are packing.
                    2. After a while observe the outside of the can.

Explanation: The outside of the can will have a sub-freezing temperature. When the atmospheric humidity is sufficiently low (i.e. below 20% at 20 degrees C.), the saturation will occur below 0 degrees C. At the temperature called the frost point, a delicate layer of frost (called white or hoar frost) will form resulting in a direct transformation of water vapor into ice. When humidity is high, the water vapor will condensate initially, and then freeze with the frozen dew not being the same as hoar frost.

Activity 6: Condensation Return to Humidity Homepage

    Materials:
                    Bottle
                    Stopper
                    Plastic tube
    Procedures:
                    1. Add a thin layer of water into the bottle.
                    2. Place a stopper with a long tube into the bottle.
                    3. Shake the bottle vigorously.
                    4. Put the free end of the tube into your mouth, and force the air into the bottle. (A bicycle pump can also be used.)
                    5. Next, let the air out quickly.
                    6. Note the results.
                    7. Take a breath of air from the bottle, and pinch the plastic tube.
                    8. Hold a lighted match near the opening and release the tube.
                    9. Allow the smoke to enter the bottle.
                  10. Force the air into the bottle again.
                  11. Compare the results with number 6 results.

Explanation: There are three basic requirements for the formation of fog or clouds: (1.) water vapor in the air; (2.) cooling to the point of saturation; (3.)
presence of condensation nuclei. Under such conditions the molecules of water vapor can begin to condense.

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