KIDS HEALTH: HOW DOES A THERMOMETER WORK?

There are many types of thermometers used around the home. The goal of each is to detect temperatures and measure temperature changes. For example:

· The thermometer outside tells you how hot or cold it is.

· The meat thermometer in the kitchen tells you meat temperature.

· The thermometer in the thermostat tells the heat or air conditioning when to turn on and off.

· The thermometer in the oven keeps the oven at a set hot temperature when it is turned on.

· The thermometer in the refrigerator and freezer maintains a set cold temperature.

· The thermometer in the medicine cabinet measures body temperature to let you know if you have a fever.

The common glass thermometer that you may have in your medicine cabinet is called a bulb thermometer; it is the same type of thermometer that is used outside to measure the climate.

Thermometers work on the principle that the volume of a liquid increases as it is heated and decreases as it is cooled. The bulb thermometer contains a fluid, usually mercury, which expands when it is heated.

When you place the thermometer in your mouth to take your temperature, the mercury in the bulb slowly warms up from room temperature to match your body's temperature. As the mercury becomes heated, it expands, rising up the tube in the thermometer.

After about three minutes, an accurate reading can be taken. Small changes in temperature are noticeable as the liquid rises and falls. If your body temperature is elevated, the mercury will rise up the tube past the 98.6 degree Fahrenheit marking to indicate that you have a fever. If your body temperature is normal, the mercury will rise to right around the 98.6 degree Fahrenheit marking, which is considered to be average body temperature.

 

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