REVIEWING
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The radiation electromagnetic is practically everywhere around us, whether by means of telecommunication (radios, television, internet, satellites). And bodies at certain temperatures also emit thermal radiation.
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The speed at which these electromagnetic waves e mechanics propagate through space is given as a function of λ ef:
Where v is the speed of the wave, λ is the wavelength, and f is the frequency at which this wave oscillates.
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The classical theory had one discrepancy related to thermal radiation from some bodies. It was expected that as a body's temperature increased, its radiated wave frequency would also increase. That is, as the body gets warmer ele would leave of the light spectrum visible and we don't we could more see you. The body would become invisible! Which does not happen experimentally. This theoretical error was called the "Ultra-Violet Catastrophe".
Graph shows the relationship between emitted radiation (R) and relation to frequency (ν)
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To get around this problem, Max Plank, after 5 years studying the subject, came to the conclusion that radiation was not emitted continuously, but in discrete packets of energy, contrary to the classical theory. These little bundles of energy he calledHow muchpower. After several experimental tests, it was proved that Max Planck's theory was able to explain the thermal radiation of bodies, arriving at a fundamental constant in nature that named it in his honor. Plank's constant.
or the reduced constant:
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The Plank theory needed to create a theoretical body (hypothetical/ideal/perfect) calledBlack Body🇧🇷 OBlack Bodyit is every body, when radiation falls on it, it absorbs all radiation in all wavelengths and also emits all radiation perfectly. In other words there are no losses na absorption or radiation emission.
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Plank then corrected the theory that had been held until then na physical classic, and the law describing the length of heated bodies was a Rayleigh-Jeans law. Plank a then makes the adjustments adopting its constant and with that the experimental data agree with the equation suggested by him:
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Plank's law respects two other important relationships when it comes to radiation from heated bodies: The Stefan-Boltzmann law and the Wien displacement law: In which the Stefan-Boltzmann law tells us the maximum intensity radiated by the blackbody and Wien's displacement law tells us that for the maximum emission of a body there is a wavelength associated with a certain temperature, in which the product of both remains constant.
- Stefan-Boltzmann law -
- Wien displacement law -
where the Stefan-Boltzmann constant is given by: