Black body radiation, Maxwell equipartition of energy It is written in my textbook that "Maxwell's law of equipartition of energy indicates that the energy radiated by a black body should be equally distributed among all the radiations emitted by it." I want to know how?
 A: From Equipartion Theorem
Is there a follow on sentence in your book that indictates that Maxwell's equipartion law was found to be incompatible with BB radiation? And that this was due to the fact that Maxwell was dealing with classical mechanics, whereas the BB spectrum required quantum mechanics, in particular the idea of discrete rather than continuous energy.

In classical statistical mechanics, the equipartition theorem is a general formula that relates the temperature of a system with its average energies. The equipartition theorem is also known as the law of equipartition,equipartition of energy, or simply equipartition. The original idea of equipartition was that, in thermal equilibrium, energy is shared equally among all of its various forms; for example, the average kinetic energy per degree of freedom in the translational motion of a molecule should equal that of its rotational motions.
Although the equipartition theorem makes very accurate predictions in certain conditions, it becomes inaccurate when quantum effects are significant, such as at low temperatures. When the thermal energy kBT is smaller than the quantum energy spacing in a particular degree of freedom, the average energy and heat capacity of this degree of freedom are less than the values predicted by equipartition. Such a degree of freedom is said to be "frozen out" when the thermal energy is much smaller than this spacing. For example, the heat capacity of a solid decreases at low temperatures as various types of motion become frozen out, rather than remaining constant as predicted by equipartition. Such decreases in heat capacity were among the first signs to physicists of the 19th century that classical physics was incorrect and that a new, more subtle, scientific model was required.

Along with other evidence, equipartition's failure to model black-body radiation —also known as the ultraviolet catastrophe—led Max Planck to suggest that energy in the oscillators in an object, which emit light, were quantized, a revolutionary hypothesis that spurred the development of quantum mechanics and quantum field theory.
However, this answer Black Body Radiation might have an answer that makes more sense to you.
A: "Equipartition of energy" means that a system in equilibrium will have all its forms (degrees of freedom) of energy the same. For example, the rotational and translational energy of its particles will be equal. A blackbody, by definition, is not only internally in equilibrium, but also by definition all its parts have complete radiative coupling with any outside sensor. (Radiative coupling refers to how quickly energy can be transferred). Since here all forms of energy are equal and any energy can be transferred instantaneously if need be, then the radiation, too, will be equal.
