Blackbody Radiation 

    A "black body" is a theoretical perfect absorber, which absorbs radiation of all wavelengths falling on it. It reflects no light at normal temperatures and thus appears black. However, like ideal gas in kinetic theory, it is a theoretical model and we may find in reality only "Almost perfect black bodies".

    It follows from Prévost's theory of exchanges of 1792 that the best radiation absorber - the black body, is also the best radiation emitter. The radiation emitted by a black body is called, you guess?... Black body radiation. (Straight forward isn't it?) It is also known as "full radiation" or "temperature radiation".

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Ultraviolet Catastrophe 

The Problem 

    In the late nineteenth and early twentieth centuries, a great deal of experimental evidence began to accumulate for which classical mechanics could provide no explanation. It was the consideration and explanation of these data which led to the development of quantum mechanics.

One of the most significant failures of classical mechanics was its inability to explain the distribution of energy emitted by a black body. Any hot object emits electromagnetic radiation, and the maximum in the emitted wavelength shifts to shorter wavelengths as the temperature of the emitter is raised.

A black body is the name given to a theoretical ideal emitter, an object capable of absorbing and emitting all wavelengths of radiation equally. A black body emitter may be successfully approximated by a small opening into a heated cavityThe emission curves of a black body have the following form:

The Classical model

1. The frequency of radiation emitted from a blackbody depends on the temperature of the blackbody. 

2. lower temperature of the blackbody the lower the energy of the blackbody radiation.  Higher the temperature of the black higher the energy of the radiation.

3. The frequency of the light is directly proportional to the energy.

What really happens

The frequency does increase as the temperature increases, until it peaks then drops off.  

    When an  object (an matter) gives up energy in the form of light, as in it's heated up, then the light released is called a photon.  

    the amount of light, the energy given off, is measured in the number of photons, not in the frequency.  Even though the frequency will increase as the temperature increase, it will peak and then fall

Planck's Solution 

   In 1900, the German physicist Max Planck proposed a bold and innovative resolution to the ultraviolet catastrophe. He reasoned that the problem was that the formula predicted low-wavelength (and, therefore, high-frequency) radiancy much too high. Planck proposed that if there were a way to limit the high-frequency oscillations in the atoms, the corresponding radiancy of high-frequency (again, low-wavelength) waves would also be reduced, which would match the experimental results.

   Planck suggested that an atom can absorb or reemit energy only in discrete bundles (quanta). If the energy of these quanta are proportional to the radiation frequency, then at large frequencies the energy would similarly become large. Since no standing wave could have an energy greater than kT, this put an effective cap on the high-frequency radiancy, thus solving the ultraviolet catastrophe.

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