If black wire of platinum is heated, then its colour first appears red, then yellow and finally white. It can be explained on the basis of
A
Wien's displacement law
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B
Prevost theory of heat exchange
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C
Newton's law of cooling
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D
Ohms law
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Solution
The correct option is A Wien's displacement law According to Wein's law λmT=constant, on heating up to ordinary temperatures, only long wavelength (red) radiation is emitted. As the temperature rises, shorter wavelengths are also emitted in more and more quantity. Hence the colour of radiation emitted by the hot wire shifts from red to yellow, then to blue and finally to white.