Correct Answer - Option 4 : does not vary with wavelength and temperature of the incident ray
Explanation:
When thermal radiation falls onto an object,
- The radiation will be absorbed by the surface of the object, causing its temperature to change
- The radiation will be reflected from the surface of the body, causing no temperature change
- The radiation will pass completely through the object, causing no temperature change
Absorptivity (α) is a measure of how much of the radiation is absorbed by the body
Reflectivity (ρ) is a measure of how much is radiation is reflected
Transmissivity (τ) is a measure of how much radiation passes through the object.
Each of these parameters is a number that ranges from 0 to 1.
Absorptivity may be a function of wavelength and/or direction, and is related to the emissivity of the region by Kirchhoff's law. The absorptivity is identically equal to unity for black bodies and is independent of temperature and wavelength for gray bodies.
