[BLANK_AUDIO]. Hi there. At the beginning of the 20th century it's probably fair to say that a major change occurred in how we understand the nature of matter and energy. Because at the at the end of the 19th century, physicists were, were feeling rather smug because all their theories could explain phenomena ranging from the motions of planets and the, say the dispersion of, of visible light by, by prisms and the, in essence, it was believed. That matter was particle in nature. And that energy, say like the visible light energy, was wavelike in nature. And, that there was a clear distinction, between these, these two, two things. At the beginning of the 20th century however, there was certain experimental results that suggested that maybe this actually exactly wasn't correct. And, the first important advance came in about 1901 and this was by the German physicist Max Planck, who we show over here. So this is Max Planck. Who's regarded usually as the father of, of, of quantum mechanics, and what, what Planck was doing, he was studying black body radiation. Or he was studying the profile of intensity versus wavelength of electromagnetic radiation emitted from a solid body, when it was heated to, to high temperatures. And if we move down here, we'll show here on the right, what kind of data this was, was, was, was, providing. Which couldn't be explained, by, classical mechanics. And this simply shows, this is a, a plot of on the, on the x-axis here you have the, the wave length of the radiation. And on our our y axis here you have the the intensity. And these occurs at different temperatures. This curve here corresponds to 3,000 degree Kelvin, a body heats to 3,000 degree Kelvin. Here a body's reheated to heated at 4,000 degrees Kelvin. And here a body heated at 5,000 degrees Kelvin. Now, at that time our classical physics would have suggested that instead of these curves going up like this and reaching a peak and then falling off at lower wavelengths. What it did, what it would have suggested, we just throw it in here and write a set for the higher one here, it would have continued on like that to to infinity. And that was because at that time it was taught that the radiation emitted from a body was of a continuous nature. So, the energy should continuously increase as the, the wavelength gets, gets smaller. Now, the great contribution of Planck to this. What Planck said was or he proposed that the only way you can explain this falling off here. At the, at the lower wave length, is that energy must not be continuous. And he proposed that the energy that was emitted from bodies like this when they were heated to high temperatures, had a certain packet of er, pack packet from the fundamental value. And you define this fundamental value in theorems of a constant, Haag, which because it was discovered by Plancks is called Plancks Constant. [BLANK_AUDIO]. And nu is the frequency of the radiation that's emitted. So, this was quite a, a, a a large jump at this time. Because prior to this, it was alls, always felt that radiation was continuous. But what Planck was saying is that radiation is composed of fundamental units times h, times nu, and that there can only be a, an integer number of these. So you have delta e is equal to nh nu, and n is going to be 1, 2, 3, 4, 5 and so on. You can't have 0.5 of h nu, or you can't have 0.65 of h nu and so forth, so they're discrete units. And also you notice here the delta e, the energy emitted is proportional to the frequency. So a very simple explanation of these curves here is that as the wavelength gets smaller, you know that the frequency is getting higher. So, actually at this level here, the packets of energy are too high. So, therefore, the as the energy is distributed around the, the body, it can't reach those values. So therefore it, it, it falls off. [BLANK_AUDIO]
