A thermometer is the instrument used to measure temperature. There are different types of thermometers, including:
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Liquid-in-glass thermometer: This is the most common type of thermometer used today. It consists of a glass bulb containing a special liquid, usually mercury or alcohol, and a stem with a scale marked for measuring the temperature. The liquids chosen for thermometers expand and contract significantly in response to temperature changes, so they indicate temperature as a position on the stems scale.
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Resistance thermometer: This type of thermometer measures temperature by detecting changes in electrical resistance. They are especially useful for measuring temperatures on surfaces that are out of reach or too hot to touch, like steam boilers, metallurgy furnaces, and hot air balloons.
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Radiation thermometer: This type of thermometer measures temperature by detecting infrared radiation emitted by an object. All objects emit infrared radiation with an intensity approximately proportional to their temperature. Radiation thermometers consist of a series of optics that focus infrared light onto a special electronic detector.
Other types of thermometers include thermocouples, which use two metal leads of dissimilar metals placed in close proximity to each other to create voltage that corresponds to changes in temperature, and infrared thermometers, which detect changes in infrared light frequency to measure temperature.
