Discussion
The monochromatic emissivity of a white body at all wavelengths and temperatures is equal to-
Answer: A
The emissivity of a white body is zero.
In radiation terms a white body is an ideal surface that reflects all the radiation falling on it, so its absorptivity is zero. By Kirchhoff's law emissivity equals absorptivity, so its emissivity is zero at every wavelength and temperature.
An emissivity of 1 describes a black body, and a constant value between 0 and 1, such as 0.6, describes a grey body. The range 0.1 to 0.4 describes no ideal body.
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