A difficult but very important concept for thermodynamics is a black body. Thermodynamics is the basis of any night vision because through a night vision device we recognize the temperature spectrum of a body or object. Of course, if you use the device, you often become interested in the physical process itself. How and what happens in the universe that we can so easily see the invisible through the device?

We have gathered for you the most common questions and answers regarding black body radiation. So that you can make sense of this fancy term without having to go back to your high school physics textbook again.

Before dealing with such a concept as black body radiation, we first need to understand a little bit of theory and terminology.

What is a black body?

An object which absorbs all the electromagnetic radiation falling on it (at all frequencies) is called a black body. According to the law of conservation of energy, this object must also emit energy in the form of electromagnetic radiation – otherwise, the absorption of the incident radiation will lead to an infinite increase in temperature. The source of radiated electromagnetic waves, for example, can be thermal vibrations of atoms and ions in the material of which this black body is "made".

What are some real examples of black bodies?

The first example of a "black body" we see in the sky almost every day is our Sun. The spectrum of the Sun at sea level is riddled with absorption by different atmospheric gases (water vapor, oxygen, carbon dioxide), but the spectral composition of solar radiation outside the atmosphere is described with good accuracy by a black body model with a temperature of 5800 K. Thus, by measuring the spectrum of the Sun, one can, without leaving Earth, measure the temperature of its surface.

Also, such physical and astronomical objects as a black body, which are expressed by the physical state when they absorb all the radiation falling on them, but reflect light or like light other radiation at the wavelength of the relative energy maximum, can be considered:

·         Active planetary nuclei.

·         Stars.

·         Black or white holes.

·         Atoms.

And, all these objects are united by strong gravitation and magnetism, which contributes to a directed flow of radiation to these objects, so that the extrinsic radiation will sink into eternity in these objects.

What is the color of a black body?

The color temperature is the temp to which you need to heat a black body in order for it to emit radiation of the same color tone as the one in question. And in simple words, we need to know that it changes from a "warm", almost red, to a "cool" blue color, passing a white "daylight" color along the way.

How does black body radiation occur?

Radiation of a black body is done in the following way. On the surface of a black body, radiation or light falls at a point through which it penetrates deep into the body. When radiation or light reaches the inner cavity, part of it is absorbed, the other part, reflected, cannot dissipate into space, it reaches the inner cavity again, and again is partially absorbed, and again reflected, and so on.

On the model of a black body, a beam of radiation at a point falls inside a hollow ball. At the point on the inner plane, part of the radiation is absorbed, the part is reflected, falling to the reflected point, where the same happens, and the remaining part is reflected at the next point. But a black body is not hollow, although it is transparent to a certain extent to radiation, therefore, the radiation passing through the black body itself loses its energy, part by part, just as it is reflected from the inner shell of the black body. Thus the process continues until all the rays are absorbed.

Does the black body emit light itself?

Absolutely not! A black body does not emit light itself. But based on thermodynamics it follows that a black body can reflect a part of any light or radiation located at the same differential wave energy maximum as the outer shell of the black body. The energy and spectrum of the reflected radiation do not depend on the composition of the black body. This property of the black body has determined the values as a benchmark in the history of studies about the color and spectrum of stars.

 

We hope that our article has helped you to understand a little more about the complex terminology of black body radiation. And when you know the basics, it's always much easier to use devices that work with those very basics.