Question
When the temperature of an object is increased slowly, why does it appear red at first?
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Answer
According to Wien's law related to radiations
$\lambda_{ m } T =$ Constant
According to this if temperature T is less then the wavelength of emitted radiation $\lambda_m$ would be more. In the visible light the wavelength of red light is maximum. So when the object is heated slowly then the wavelength of emitted radiation at low temperature will be maximum so on heating an object the radiation waves with big wavelengths (of red colour in visible light) are emitted first, and the object appears red at first.
$\lambda_{ m } T =$ Constant
According to this if temperature T is less then the wavelength of emitted radiation $\lambda_m$ would be more. In the visible light the wavelength of red light is maximum. So when the object is heated slowly then the wavelength of emitted radiation at low temperature will be maximum so on heating an object the radiation waves with big wavelengths (of red colour in visible light) are emitted first, and the object appears red at first.
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