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Chapter 1, Lesson 3 Multimedia

Heating and Cooling a Thermometer

Molecules are represented as circles to show how the movement and distance between molecules increase with increasing temperature.

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  • When the thermometer is cooled, the molecules move more slowly, get closer together, and move down in the tube.
  • When the thermometer is heated, the molecules move faster, get slightly further apart, and move up in the tube.

Molecules in a Thermometer

Two thermometers, one recording a high temperature, the other recording a low temperature.  The molecules of the liquid in the thermometer are further apart and have more movement in the thermometer recording a high temperature. The molecules are closer together and exhibit less movement in the thermometer recording a low temperature.
  • The molecules of the thermometer in hot water should be randomly arranged, slightly further apart, moving faster.
  • The molecules of the thermometer in cold water should be randomly arranged, closer together, moving slower.

Different Thermometers, Same Temperature

At left an therometer where the internal fluid is alcohol. At right, a thermometer where the internal fluid is mercury. Both thermometers are reading 100 degrees Celsuis, but the fluid in the alcohol thermometer is much higher than the fluid in the mercury thermometer.
  • If the temperatures are the same, why are the liquids in the two thermometers at different heights?