One of the experimental results that most caught the attention of scientists in the late nineteenth century was the study of the light emitted by bodies when they are very hot, such as "hot iron" or even a coal in embers. Blacksmiths at the time already knew that when iron turned red, its temperature was around 1,000 K, making it easier to work.
In order to study the light emitted by hot bodies, a model was proposed in which the idea was to perform calculations only on the radiation produced by the thermal agitation of the body. Such a body should absorb all the radiation that reached it, not being able to reflect it. Thus, the body would have to be completely black, hence the name of the model: blackbody radiation.
When looking to the past, taking into account what we know today, we can affirm that the study of black body radiation marks the emergence of Quantum Mechanics.
First, we have to really understand what blackbody radiation is. When we heat a body, it starts to emit electromagnetic radiation. Thus, we can say that the spectrum of this radiation depends on body temperature. For example, the furnace of a steel industry or the sun produces radiation through thermal agitation. If we look at the red-hot coals, we will actually see blackbody radiation from a body at very high temperature.
filament lamp
An example of blackbody radiation that we have in everyday life is the filament lamp. When an electric current passes through the filament of the lamp, it heats up by the Joule effect and behaves practically like a black body. When the temperature gets close to 2000 K, some of the energy is emitted as visible light, which is used for illumination. However, a good part of the thermal energy is emitted in the infrared spectrum and is not used in lighting.
In order to increase the lighting efficiency of an electric lamp, it is necessary to increase the temperature of the filament. In order for it to produce light similar to sunlight, the filament must operate at a temperature similar to the surface of the Sun, which is approximately 5,700 K. The tungsten used to make lamp filaments has a melting temperature of 3137 K.
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By Domitiano Marques
Graduated in Physics
Brazil School Team
Modern physics - Physics - Brazil School
Would you like to reference this text in a school or academic work? Look:
SILVA, Domitiano Correa Marques da. "Black body radiation"; Brazil School. Available in: https://brasilescola.uol.com.br/fisica/radiacao-corpo-negro.htm. Accessed on June 27, 2021.
