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The Challenge: Make a Thermometer

How are modern thermometers made?

The most common kind of thermometer consists of a liquid, such as alcohol or mercury, in a very thin, hollow glass tube. It works because of the fact that liquids expand more than solids as their temperatures increase. If both the liquid and glass expanded equally, the whole thermometer would simply increase in size. Instead, what actually happens is that the liquid expands more than the glass and moves up the capillary, registering a change in temperature. Thermometers are usually calibrated with a certain range of temperatures in mind. For example, a clinical thermometer used to measure human body temperature might only have measurements ranging from 32°C to 42°C (90-107°F).