Heat and temperature
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5. Measuring temperature

Figure 7.4.
The red liquid in the thermometer is alcohol. Alcohol expands uniformly over a wide range of temperatures. This makes it ideal for use in thermometers.
Look at the common thermometer pictured in the figure on the right.


The red liquid rises or falls in the glass tube as the temperature changes. Temperature is read on the scale at the height of the liquid in the tube.

Q&A

Q: Why does the liquid in the thermometer expand and contract when temperature changes?

A: When the temperature is higher, particles of the liquid have greater kinetic energy, so they move about more and spread apart.
This causes the liquid to expand.

The opposite happens when the temperature is lower and particles of liquid have less kinetic energy. The particles move less and crowd closer together, causing the liquid to contract.

Click on the image to open a simulation that shows this thermal expansion.

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