Question

What are the four laws of radiation?

Answer 1

Hint:When attempting questions based on radiation like the one given to us above, keep in mind the various concepts and terms related to radiation, and the different laws governing the same. Keep in mind the different factors which relate with radiation and how the factors affect radiation.

Complete step-by-step solution:
The four laws which explain radiation are Kirchhoff’s law, Stefan-Boltzmann’s law, Planck’s law and Wien’s displacement law.
Now when we talk about radiation, one thing which we need to understand is that all bodies radiate energy. The form in which they radiate energy is known as photons, and when these particles reach another surface they either get absorbed, reflected back or transmitted. Absorptivity (\[a\]) is a term which is also referred to as a particular fraction of incident radiation which is absorbed. Reflectivity (\[r\]) can also be known as the fraction of incident radiation which is reflected back. And lastly, we have transmissivity (\[t\]) which is also known as the fraction of incident radiation which is transmitted.
Kirchhoff’s law basically states a relationship\[a=e\], which implies simply that good radiators are also good absorbers. But this law is only valid when the mentioned body is in thermal equilibrium with the surrounding.
The second law is Stefan-Boltzmann’s law which basically states that the amount of radiation which is emitted per unit given time, from a particular area of a black body at an absolute temperature \[T\]will be directly proportional to the fourth power of the temperature, which can give an equation;
\[\Rightarrow \]\[\dfrac{u}{A}=\sigma {{T}^{4}}\]
In Planck’s law of radiation, the law basically depicts the electromagnetic radiation that is emitted by a black body when it is in thermal equilibrium and at a definite temperature. This law is extremely useful and became a pioneer for future modern physics and quantum theory.
Wien’s law or more commonly called Wien's displacement law tells us about the relationship between the temperature of a black body and the particular wavelength at which it emits the most light.

 Note:A black body is a material which is ideally a substance which can emit and absorb all frequencies of light, and is supposed to be a great absorber and reflector of light. Energy released by a black body is known as black body radiation and it can be of various types like thermal radiation, cavity radiation etc.