Measuring Temperature
We measure temperatures with a thermometer. How does a thermometer work?
One familiar thermometer is the glass thermometer. This consists of a long, thin glass tube with a bulb full of liquid at one end. For a room thermometer, this liquid could be alcohol with a red dye. For a body thermometer, this liquid would be mercury.
The way a mercury thermometer works is that the liquid expands when heated. The mercury then moves through the narrow bore of the glass tube, like a thread. There are markings along the tube that tells us the temperatures for different lengths of the thread.
The mercury thermometer makes use of the property that the volume of mercury changes with temperature. Marking the glass tube essentially means measuring changes in the volume.
A simple way would be to mark the mercury positions at ice point and steam point, and then make 100 marks in between. This gives the familiar Celsius scale, in which ice is at 0 degree Celsius, and steam at 100 degrees Celsius.
This suggests that if there is a property of any material that changes with temperature, then it can be used to measure temperature.
One example is the electrical resistance of a piece of metallic wire. Another example is the pressure of a bottle of air. Both change with temperature. Measuring the resistance or pressure is more tricky than measuring the length of a mercury thread in a glass tube, but it can be done.
Copyright 2010 by Kai Hock. All rights reserved.
Last updated: 13 October 2010.