Question

If black wire of platinum is heated, then its colour first appear red, then yellow and finally white. It can be understood on the basis of

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

Answer 1

The correct option is A

Wien's displacement law

According to Wein's law ${\lambda }_{m}T$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.