12.21 Measurement of High Temperatures by Radiation
At high temperatures above the melting point of gold (1063°C), the difficulties of gas thermometers are too high. Hence, they are of no use in establishing the thermodynamical scale of temperature. Thermometers based on laws of radiation are wonderfully suited for the measurement of high temperatures beyond the limit of gas thermometer.
We have seen that the radiation inside an enclosure whose walls are maintained at a constant temperature is unique in character and is independent of the nature of walls of the enclosure. Further, the radiation inside such an enclosure behaves as a perfect gas. Hence, radiation inside the enclosure can be used as the thermometric substance for defining a scale ...
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