Objective:
– To illustrate an application of bimetallic expansion in the form of a car thermostat and hair dryer
Apparatus:
Car Thermostat
- Clamp stand
- Bunsen burner
- Sparker (or lighter)
- Digital thermometer
- Ring clamp with ceramic screen
- Beaker
- Thermostat
- (Optional: electric kettle to pre-heat water)
Hair Dryer
- hair dryer coil with bimetal contact (see picture below)
- lighter
Method:
(Optional but highly recommended: preheat enough water to fill the beaker in the electric kettle.)
Show students the room-temperature (closed) state of the thermostat. Point out the closed main valve. You may wish to pour some (cool) water on the top centre to demonstrate that it is a water-tight seal.
Place the thermostat in the beaker. Cover with (preferably preheated) water. Place thermometer in beaker. Heat the water with the Bunsen burner.
When the water temperature reaches approximately 88 ‘C, the main valve will open. Students can observe this in the beaker. Alternately, you can fish the thermostat out of the water to show them, as it takes a few minutes to cool down and close again. You may wish to now pour some water on the top centre to demonstrate that water can flow through.
If you wish to return the thermostat to its closed state rapidly, run cool tap water over it.
“How Thermostat Works” – Video Created by Engine On for Mechanical and Automobile Animations.
Here is a bimetal plate contact in a hair dryer. Use a lighter to heat the plate and the contact will open.
