Black body radiation

Black body radiation is a fundamental concept in physics that describes the thermal radiation emitted by an idealized object known as a black body, which absorbs all incoming light without reflecting any. In real life, this concept is crucial for understanding how objects like stars, including our Sun, emit energy. For instance, the warmth we feel from the Sun on a sunny day is a result of black body radiation. This phenomenon is also essential in designing technologies like incandescent light bulbs, where the filament glows when heated, emitting light similar to a black body. Moreover, black body radiation plays a vital role in astrophysics, helping scientists determine the temperature and composition of distant celestial bodies. Understanding black body radiation not only deepens our knowledge of the universe but also enhances practical applications in various technologies we use every day.

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Black Body Radiation

Black body radiation refers to the electromagnetic radiation emitted by an idealized object called a black body, which perfectly absorbs all incoming radiation and reflects none. This concept is pivotal in physics as it helps explain how objects emit energy based solely on their temperature, without regard to their material composition or surface characteristics.

Properties of Black Body Radiation

• A perfectly black body is one that completely absorbs the radiations of all wavelengths incident on it.
• A perfectly black body neither reflects nor transmits any radiation; therefore, the absorptance of a perfectly black body is unity. I.e a=1
• The colour of an opaque body is the colour (wavelength) of radiation reflected by it. As a black body reflects no wavelength so, it appears black.
• When a perfectly black body is heated to a suitable high temperature, it emits radiation of all possible wavelengths. For example, the Sun is an example of a black body. As its temperature is very high and it emits all possible radiation.
• A perfectly black body is an ideal concept and it can’t be realized in practice. But materials like Platinum black or black come close to being ideal black bodies. Such materials absorb 96% to 85% of the incident radiations.

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Summary

Black body radiation is seen to be a theoretical spectrum of electromagnetic radiation, which perhaps could be radiated from that ideal object known as a black body—an object that absorbs all radiation falling on it and doing so by reradiation, depending only upon its temperature. This radiation's spectrum is dependent upon the temperature of the black body and follows definite laws. Planck's law describes the intensities of radiation at all wavelengths, while the Stefan-Boltzmann law relates the total energy radiated per unit area to the fourth power of the black body's temperature. Wien's displacement law states that peak wavelengths go toward shorter wavelengths as the temperature rises.