Mercury in a thermometer is a liquid. What property of a liquid does a thermometer use?

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Mercury thermometers make use of the following properties of liquids:

  • Liquids have no set shape.  Because mercury has no set shape, it can conform to the shape of the glass tube that the thermometer is made from.
  • Liquids expand when heated and contract when cooled.  This is obviously very important for a thermometer.  It is because of this property of liquid that the mercury can go up the thermometer tube as the temperature goes up.

Mercury is not the only liquid that can be used in a thermometer.  However, mercury is ideal in part because it expands at a very constant rate over a large range of temperatures.

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