Today, I want to talk about how Max Planck's quanta idea came about and how it solved the Ultraviolet Catastrophe. But in order to explain this, I first need to go into black body radiation.
Black bodies, simply, are the ideal physical objects for absorbing electromagnetic radiation. So, just imagine a box painted in matte black (the best colour for absorbing radiation). Also, in contrast, there are white bodies which reflect EM radiation perfectly. So, as EM radiation hits the black body from the surroundings, the black body absorbs it. However, this cannot go on forever without the 2nd law of thermodynamics (energy cannot be transferred from one body to a hotter body) being violated. So, after the black body becomes the same temperature as its surroundings, thermal equilibrium, it radiates out the EM radiation. How this happens is that the energy from the EM radiation would approach the atom and the energy is transferred to the electron, which then jumps up an energy level. However, because this is unstable, the electron wants to return to a low energy state and in doing so, releases energy. This released energy, of course, has to be the same as the energy absorbed to conserve the energy. And this released EM radiation should have a wavelength. Also, because all EM radiation travels at the speed of light and the speed of a wave is the frequency times the wavelength, as the frequency increases, the wavelength reduces (the speed is constant). What we expect, according to the Rayleigh-Jeans Law is that as the wavelength of the radiation emitted from the black body decreases, the intensity increases. So, according to this, everything should appear violet and the UV rays emitted would have high intensity, which would be disastrous, considering its effects on us (induces cancer). However, in reality,this is not the case. Instead, the intensity peaks at a point and then drops after so that the intensity of UV light is not so strong. This difference in theory and reality could not be explained by any of the classical physicists of the era and was called the Ultraviolet Catastrophe.
So in comes Max Planck, a german physicist with a revolutionary idea that gave birth to quantum physics. And this idea was energy quantization. He proposed that energy (such as light) came in fixed packets and the energy per packet was determined by the equation "E=fh", which means that frequency of the wave multiplied by Planck's constant would give the energy. These packets of energy were called quanta (singular form is quantum). And for UV light, since its wavelength is low (which means its frequency is high) the energy per quantum is high. In a Maxwell Boltzmann Curve, we see that there are an abundance of particles at the modal energy level but there seem to be less of particles with higher energy. In a similar way, the photons with higher energy, such as those with UV light wavelength, have a lower possibility of existing and there are much fewer of them there. So this explains the drop in intensity after the peak in the wavelength intensity graph.
Black bodies, simply, are the ideal physical objects for absorbing electromagnetic radiation. So, just imagine a box painted in matte black (the best colour for absorbing radiation). Also, in contrast, there are white bodies which reflect EM radiation perfectly. So, as EM radiation hits the black body from the surroundings, the black body absorbs it. However, this cannot go on forever without the 2nd law of thermodynamics (energy cannot be transferred from one body to a hotter body) being violated. So, after the black body becomes the same temperature as its surroundings, thermal equilibrium, it radiates out the EM radiation. How this happens is that the energy from the EM radiation would approach the atom and the energy is transferred to the electron, which then jumps up an energy level. However, because this is unstable, the electron wants to return to a low energy state and in doing so, releases energy. This released energy, of course, has to be the same as the energy absorbed to conserve the energy. And this released EM radiation should have a wavelength. Also, because all EM radiation travels at the speed of light and the speed of a wave is the frequency times the wavelength, as the frequency increases, the wavelength reduces (the speed is constant). What we expect, according to the Rayleigh-Jeans Law is that as the wavelength of the radiation emitted from the black body decreases, the intensity increases. So, according to this, everything should appear violet and the UV rays emitted would have high intensity, which would be disastrous, considering its effects on us (induces cancer). However, in reality,this is not the case. Instead, the intensity peaks at a point and then drops after so that the intensity of UV light is not so strong. This difference in theory and reality could not be explained by any of the classical physicists of the era and was called the Ultraviolet Catastrophe.
So in comes Max Planck, a german physicist with a revolutionary idea that gave birth to quantum physics. And this idea was energy quantization. He proposed that energy (such as light) came in fixed packets and the energy per packet was determined by the equation "E=fh", which means that frequency of the wave multiplied by Planck's constant would give the energy. These packets of energy were called quanta (singular form is quantum). And for UV light, since its wavelength is low (which means its frequency is high) the energy per quantum is high. In a Maxwell Boltzmann Curve, we see that there are an abundance of particles at the modal energy level but there seem to be less of particles with higher energy. In a similar way, the photons with higher energy, such as those with UV light wavelength, have a lower possibility of existing and there are much fewer of them there. So this explains the drop in intensity after the peak in the wavelength intensity graph.
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