Thermometers measure temperature according to well-defined scales of measurement. (credit b: modification of work by Tess Watson credit c: modification of work by Lamel J. Such thermometers are more accurate than the alcohol thermometers placed under the tongue or in the armpit. Infrared thermometers are also frequently used to measure body temperature by gently placing them in the ear canal. The pyrometer measures infrared radiation (whose emission varies with temperature) from the vent and quickly produces a temperature readout. (c) A firefighter uses a pyrometer to check the temperature of an aircraft carrier’s ventilation system. When the temperature reaches above 96.8 ° F 96.8 ° F, the second liquid crystal square also changes color, and so forth. When the plastic thermometer is exposed to a temperature of 95 ° F 95 ° F, the first liquid crystal square changes color. Below 95 ° F 95 ° F, all six squares are black. (b) Each of the six squares on this plastic (liquid crystal) thermometer contains a film of a different heat-sensitive liquid crystal material. When the thermometer’s temperature increases, the liquid from the bulb is forced into the narrow tube, producing a large change in the length of the column for a small change in temperature. (a) In this common type of thermometer, the alcohol, containing a red dye, expands more rapidly than the glass encasing it. Figure 1.3 Because many physical properties depend on temperature, the variety of thermometers is remarkable.
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