I find this concept a little confusing, mainly because of how simply my teacher explained it. Can someone please explain the concept (or what we need to know of it for the hsc). Thanks.
This is for planks theory right? Explain why black body emissions need to be quantised or whatever?
Basically you need to know this:
Analogy:
A black body can be thought and modeled as a very hot oven with a little hole in the side. Energy going into the oven bounces around and is absorbed, and energy coming out of the oven is that which is characteristic of the temperature of the inside, so it's at equilibrium with it. Thus, this model is basically a black body (perfect emitter/absorber).
Now, when this was modelled and records taken, the classical theory predicted that as wavelength decreased, the insensity of the emissions would increase, similar to a branch of a hyperbola. However, as the wavelength became really small, the emissions would be huge, and have much more energy than the system, so energy is not conserved, so this cannot work for the high wavelength ones. Basically classical theory predicted if the energy were to be shared between the particles in continuous units, there would be a lot at low wavelengths and hardly any at high wavelengths. However, it does explain why at large wavelengths, the intensity approaches zero. This is because there is relatively few methods a particle can oscilate to create a wave in the "cavity" of our oven. Thus, since the wave cannot be formed in such a space, the wavelength restricts the waves that can be radiated.
However, by assuming that energy must be quantised, Plank solved the issue of infinite energy. As the electrons have some energy, the higher the wavelength, the higher the energy of the emission needed (E=hf). Plank proposed that discrete packets were needed, such that only all or none of the energy was given off, so to produce a photon of energy E=HF, the electron must have this energy. As freq. increases, and wavelength decreases, few electrons will have enough energy to emit a photon of E=hf, and half energy emissions etc cannot be done.
So, at low frequency, the long wavelength limits the number of possible photons. At high frequency, the high energy makes emission unlikely. So the distribution goes to zero at both f = 0 and f = infinity, and has a maximum in between.
