Articles

    Thermometer Thoughts

    Kids, how would you like to make your own thermometer? All you will need is some water, rubbing alcohol, a clear, narrow-necked plastic bottle, food coloring, a clear plastic straw, and tape or modeling clay. Here is what you do:

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    1. Pour equal volumes of rubbing alcohol and water into the bottle. You want the bottle to be at most 1/4 full.
    2. Add a couple drops food coloring.
    3. Put the straw in the bottle such that the bottom is under the liquid, but not touching the bottom of the bottle.
    4. Fix the straw in place using tape or clay. Seal the bottle so that air can not get in or out of the bottle around the straw.
    5. Heat the bottle and watch what happens. The easier way is to hold it in your hands for a few minutes.
    6. You can cool the bottle by putting it in the fridge.

    Congratulations - you just made a thermometer! Just like any thermometer, the liquid expands when warmed. This makes the liquid no longer fit in the bottom of the bottle. As the alcohol expands the colored mixture moves up through the straw. You can watch your thermometer and see how the liquid changes throughout the day. What happens if your thermometer is in shadow or in sunlight? The liquid should go up the straw with heat and down the straw when cooled (hopefully not all the way or the thermometer might not work anymore).

    Why does the level of the liquid change with temperature? Because the air in the bottle changes volume with temperature. As air is heated it either expands or exerts more pressure. In trying to expand and in exerting pressure, it fights gravity and pushes some liquid up the straw. Most common thermometers work with exactly these principles.

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    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    kcarrado@anl.gov
    November 2007

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    Reference:

    http://www.energyquest.ca.gov/projects/thermometer.html   and
    http://experimentopia.org/experiment/build_your_own_thermometer