University of Virginia
Physics Department

How Does a Thermostat Work?

A Physical Science Activity

Student Activity




  1. The thermostat must already be mounted vertically on a board or backing that is firmly placed. The students should not handle the thermostat, but they should carefully examine it.
  2. Locate the bimetallic coil and the mercury bulb. Sketch a diagram of the thermostat in your data table, labeling any important parts.
  3. Plug in the hair dryer. Blow hot air on the bimetallic coil. Observe what happens and record your observations.
  4. Switch the hair dryer so that it blows cold (or room temperature) air. Observe any changes in the thermostat structure and record these.
  5. Alternate the temperature of air on the thermostat. Observe the time it takes for the change in temperature to affect the position of the glass bulb.


Data Sheet

Diagram of Thermostat:




Observations after applying hot air:




Observations after applying cold air:




Observations after alternating temperatures:





1. Explain how a bimetallic coil reacts to a change in temperature.



2. Explain in your own words how a change in air temperature impacts the function of a thermostat.



3. Name an application of thermostats other than to regulate the temperature of your house.