A black platinum wire, when heated, first appears dull red, then yellow, then blue and finally white. Explain.

Options

A. Wien's displacement law
B. Prevost theory of heat exchange
C. Newton's law of cooling
D. None of the above

Answer

A

Explanation

According to Wien’s law on heating up to ordinary temperatures, only long wavelength (red) radiation is emitted. As the temperature rises, shorter wavelengths are also emitted in huge amount. Hence the colour of radiation emitted by the hot wire shifts from red to yellow, then to blue and finally to white.