What is Stefan Boltzmann law?
Stefan and Boltzmann enunciate a formula about the degree of the radiate temperature of a black body.
Formula: The total amount of radiate temperature in a second from a single area of an ideal black body is proportional to the absolute temperature of the fourth power of the object.
If the radiate temperature in one unit of an ideal black body is E and the absolute temperature is T, according to the formula E∝ T4 or E=KT4
Here, K is a constant, whose value is assumed = 5.7×10-8 W/ T4m2
If the object is not an ideal black body then the equation will be, E=eKT4
Here, e= the value of relative emissivity is with 0-1.
In reality, the pyrometer is not only accepting the temperature from a radiation source, but the source has also radiated some temperature, in that case, the radiation of pyrometer is E=K(T24 – T14)
T2= the temperature of the radiation source.
T1=the temperature of the pyrometer.
How to Temperature measure by Radiation
Temperature is generated with a different wavelength. Any hot object radiates energy (or heat) around it. As the temperature increased, the intensification of radiation increases and the wavelength of average radiation decreased. Again, if the temperature is decreased, the intensification of radiation is increased. Temperature radiation has mainly consisted of some electricity magnetic wave.
From 0.3 to 0.8 microwave length effects on the retina of human eyes and consists of light. Thermal wavelength, which is more or less from it, we cannot see it but it produces heat. The intensification of black body radiation is shown in the following diagram.
In the figure, the radiation intensification of black body is 500° C. In this temperature, some radiation wave become very small and cannot create visible light, but gradually the object becomes red. If we increase the temperature more, the wavelength of light is increased and when the object becomes white, warm then we can notice the radiation of Infrared ray. During this time, there is a slight radiation of UV ray too.