Materials Required:
l 2 thermometers, 1, or both, with an exposed bulb
l Cloth
l Thread
l Water
l Electric fan
Procedure:
- Make sure the two thermometers give identical readings. Wrap a piece of lightweight cloth once around one of the exposed thermometer bulbs, and tie it in place with thread.
- Wet the cloth with water, then hold both thermometers, side by side, in front of a blowing fan. After a few seconds have passed, read the temperatures. The thermometer wrapped with a wet cloth has a lower reading than the unwrapped thermometer.
This Is What Happens:
The fan helped to blow moisture from the wet cloth into the air. This evaporation of moisture into the air requires heat. The necessary heat was taken from the thermometer bulb, which caused the liquid inside to become cooler and the temperature to drop. No such forces were acting on the other thermometer, so it did not lose heat.
