 Hi, I'm Zor. Welcome to Neuzer Education. Today we will talk about spectroscopy. Well, this is based on whatever we have learned before, the theoretical material about how the atom is structured with electrons in different shells. And this is basically a practical usage of this particular property of matter, if you wish. This lecture is part of the course called Physics for Teens, which is implemented on Unizor.com website. Website is free, there are no advertisement, no strings attached, so you can use it as a primary source of your information. If you found this particular lecture on YouTube or somewhere else, it's just stand by itself in that environment. On Unizor.com it's part of the course, which means there is a menu, a hierarchical menu, which basically leads you in logical sequence from one lecture to another. And then there is a prerequisite course on the same website, it's called Math for Teens. And definitely mathematical knowledge is absolutely mandatory to learn physics. So if you want you can take that course as well. Okay, so what's interesting about spectroscopy? It allows to do certain things which are, well, without it you cannot even imagine how you can do it. For example, measure the temperature of star. Star is far away, all we have is some kind of light, and basically it just seems to be like fantastic kind of things. But we can, and we also can establish something like composition of what kind of elements are in that star. And it can be used for many other purposes. So let me start from the beginning and remind you something which we actually addressed in previous lectures. And that's all about electrons which are circling around a nucleus. For every element we were talking about certain shells. Well, you can talk about orbits, but it's better to talk about shells. It kind of represents the three-dimensional structure of the atom. Electrons are circulating around a nucleus which contains protons, the same number of protons as the total number of electrons in atom. So the radiuses of these shells are not contiguous numbers from zero to whatever. There are certain fixed levels on which these shells are in every atom, and it's specific for every element. So we talked about atom of hydrogen, and we even had a formula that energy levels, and there are certain number of energy levels based on certain number of shells. Every shell has certain energy level. It's equal to 13.6 times 1 over n square of electron volts. Electron volt is energy unit. It's basically energy of one electron which is moving between two different potentials. The difference between the potentials is one volt. We talked about this before in the lecture. Now n is the shell number, and 13.6 is just the coefficient specific for atom of hydrogen. It can be derived theoretically, but we're not going into it right now. What matters is that every shell, and as you see, shells are increasing in its energy, and the higher the shell, the greater its energy is in algebraic sense, because the energy of electron, potential energy of electron, is negative, because to create the atom, we have to take the nucleus and take the electron from infinity and put it in the proper position on the orbit around the nucleus, right? And it's not we who are spending energy. It's basically the field itself, because protons and nucleus are positive, electron is negative, so it actually does it by itself, which means energy, potential energy is negative. It's the other way around to put it back to infinity, we have to spend energy. So that's why it's negative. But I'm just talking about absolute value of this energy. So whenever you increase the radius of the orbit, whenever the shell goes further from the nucleus and is increasing, which means if this is negative in absolute value, it's increasing, but in consider it's negative, it's increasing in its energy level. It gets absolutely smaller and smaller, so being negative, it's increasing. So whenever you consider any particular shell, there can be electrons on this shell. Now, in a normal state, the atom of hydrogen had only one electron and it's on shell number one. And this is so-called ground-level shell, and this is a stable condition of hydrogen. Now, if you supply energy to this atom, these electrons are supposed to consume, absorb this energy. Now, what do they do with this energy? Well, they move to a higher level, let's say n equals 2, and they move to this. How can it be done? Well, you can heat it up, you can put a bright light on it. Whatever the source of electromagnetic oscillation you can provide, it can be basically either, it's a radiation, whatever the frequency of this radiation is. It can be a low frequency, like heat, or it can be high frequency, like gamma rays or whatever else. It doesn't really matter. Whenever certain amount of energy goes into this particular atom, electron is supposed to somehow absorb it, so it moves to a higher level of energy. So, we give it some more energy, and this energy is used by electron to move to another orbit further from the nucleus, increasing its potential energy. Now, what happens next? Well, if enough electrons are moving to higher orbit, it's not as stable condition, so they start moving back spontaneously and releasing that potential energy. So, their potential energy from minus something goes to another radio, which is basically smaller, negatively smaller, and release this particular amount of energy. And here is important stuff. And again, we did talk about this before, I'm just repeating. Whenever it jumps here, it's releasing amount of energy equals to difference between, let's say it goes from shell number M to shell number N. So, this is number N, and this is number M. So, whenever it goes from here to here, it's supposed to release exactly this amount of energy, where N are used in this formula. Now, amount of energy which is released as a photon, one photon, one electron, jumping from one orbit to another is releasing of one photon. Now, what kind of photon? Well, here it is. Now, this is the formula again addressed before. H is a Planck constant, with a specific value for this constant. F is a frequency of electromagnetic oscillations, and this is the energy of this. So, this is one photon, one unit of energy carried by the electromagnetic oscillations of frequency F. Again, this is a quantum theory. It might seem a little bit odd, at least it definitely did seem a little bit odd in the beginning. But gradually, considering all the experimental confirmation of this theory, it looks fine, up to like 10 to the minus 8 precision experimental data agreed with the theory. So, this is the theory. It's a current model of the world, and it seems to be very precise, as far as our experiments are concerned. So, whenever you have this particular energy released by electron jumping from one to another, it's supposed to release a specific amount of electromagnetic oscillations, and this is one photon, which obviously from here has this particular... I'm just resolving it for F. This is frequency. Frequency, and as far as wavelengths, it's what is C over F, right? Or the same thing as C times tau, where tau is a period. So, we basically have frequency and wavelengths... C is speed of light, obviously. We have frequency and wavelengths, whenever electron jumps from here to here. Now, there are many different orbits. I mean, in theory it goes to infinity, right? So, they can go and go and go. Well, in practical sense, obviously that's probably not the case, but as far as we know, as far as we observe, basically, what we can say is that the difference between these two, between these two for different m and n... Now, it's getting smaller if numbers m and n are bigger, right? For instance, if you have 1 over 1000 square and 1 over 999 square, the difference between them is not exactly the same as between the first and the second orbits. It's 1 over 1 over 1 over 4, right? The first is 1 over 1, which is just 1, and the second one is 1 over 2 square, which is 1, 4, so it's 3 quarters. Now, the difference, obviously, is getting less and less as we go further from the atom, from the nucleus of the atom. If energy is smaller, when it jumps from one level to another, the frequency is smaller as well, so it's not actually a visible light anymore, because the smaller you go to infrared, you go to radio waves, microwaves and radio waves, et cetera, very long waves. Now, whenever you go closer, when it jumps from here to here, the first and second, let's say, exchange between number 2 and number 1, we will have a bigger difference between the energy levels, right? So, the frequency becomes greater and it actually falls into visible light, or might even go into ultraviolet light. So, somewhere in between, there are even visible frequencies and wavelengths of the light. And now let's go back into our original comment about the stars. So, we see the light from a star. Now, it seems like white, maybe with a little bluish kind of hint. So, let's do with this light the same as, let's say, Newton did with the sunlight. He took a prism and light goes into spectrum. Remember this? So, by splitting the light from the star into its spectrum, we can see which lights are here. Let's say you have a red and blue, for example. Well, we can measure exactly the frequency or the wavelengths of every individual line which we see in the spectrum. So, it's not like a range. I mean, we feel like a red light from this wavelength to that wavelength, but there are certain devices which can exactly determine the wavelengths or the frequency of that particular light. So, we can actually identify are these numbers, these colors, numbers, I mean, frequency number or wavelength number, correspond to any element that we know, for instance, again. In case of hydrogen, we have certain different variations, from number 2 to number 1 electron jumps and release one particular photon of energy and one particular wavelength of that photon, from 3 to 1, from 4 to 1, from 5 to 1. This is what can be actually seen if this particular atom goes from excited state to standard, to normal ground state. Then, from 3 to 2, from 4 to 2, from 5 to 2, etc. From 4 to 3, from 5 to 3, etc. We did have this particular exercise in one of the previous lectures. So, there are certain finite number of visible lights which really fall in the visible category, which we can see. Let's say it's from 4 to 2 and for 5 to 2, for example. For hydrogen, that's something else, I don't remember what it is. But there are certain specific, for this particular element, for hydrogen, kinds of photon, kinds in terms of frequency and wavelengths, which can be actually observed. So, we will compare. Are these lines which we see from a spectrum of the star correspond to one of the known wavelengths or frequencies of light whenever any particular element is getting relaxed after excitement? Well, maybe it's a hydrogen, maybe it's iron. What's the difference between iron and oxygen and hydrogen and other elements in this particular sense? Well, the difference is that there are different shells for different elements. Different shells and different differences between the energy levels of the shells and therefore different frequencies of the light which is emitted when electrons jump from one to another. So, for every element, there are certain finite number of visible light frequencies, wavelengths, which can be observed. And to tell the truth, I don't think if anything is repeated the same, exactly the same wavelengths repeated between two different elements. I don't think it happens because the precision is relatively high. And if you go with the wavelengths down to like three or four decimal points, precision of the wavelengths, you will not have elements which have exactly the same emitted wavelengths. So, by comparing the observed wavelengths of the light coming from the star with known, and obviously we have already experimentally found what kind of lights are in the spectrum of every element, well, not every but most of the elements, then we can compare and see which elements are present in that particular light of the star, which means in the star itself. Now, why, by the way, the star emits all this light? Well, because it's the source of energy. There is a nuclear reaction which is happening. It's the source of energy. What does this energy do? It moves electrons of all the elements which are inside the star to higher orbits and then the energy is continuing pumping because the energy is basically doing something like nuclear reaction. Electrons eventually will have to jump back because they cannot infinitely consume energy because if energy is consumed, which means that there is no light from the star, right? The star is dead. But if the light emits light, it means that the star is actually alive and electrons are going up whenever they're heated up and then going down, emitting the photon. So that's how the light actually is emitted. So we can distinguish what kind of elements are in that star. Now, what about temperature? Well, think about the piece of iron which you put into the fire. Well, first it starts glowing with a red color, right? Then it can be a little whiter, even bluish at some point. Why? Well, obviously red and blue and some other colors are emitted as a result of the electrons jumping from orbit to orbit from shell to shell. But the higher temperature, the more energy is supposed to be released. More energy is released, greater the frequency. Greater the frequency, the light goes from the red, which is lower frequency, into the bluish spectrum, part of the spectrum, which is higher frequency and shorter wavelengths, right? So the hotter this piece of iron, the more its spectrum moves, spectrum of emitted radiation, it moves from the red to the blue. So same thing with stars. If we have certain elements we have already established, we can actually judge by intensity. Now, if red, let's say, is more intense than blue in the spectrum, it means it's less temperature. If the blue is more intense than the red, it's greater temperature. So knowing basically the elements from which the star is composed and knowing the relative strengths of radiation emitted in every particular part of the spectrum, the more it's towards the bluish part of the spectrum, the higher the temperature of the star. And again, we have some scale and we can do that. Well, I primarily repeated most of whatever I was just saying today from the previous thing. So spectroscopy is analysis of the composition and maybe temperature of something like a star, for example, based on splitting the light into spectrum and analyzing what kind of colors are present. Well, actually, not only colors, colors we are using for visible light, but obviously our devices are sensitive not only to visible light, but also to ultraviolet light to infrared and radio waves and gamma rays, etc. So we have devices which are covering the whole spectrum of radiation. And I was just using the visible spectrum to kind of more... I think it's just more understandable. But again, using devices which analyze the spectrum, we can relatively precisely determine the composition of the star and this and the temperature. Now, it can be used for some other purposes. So there is a device called spectroscope which basically does with anything what we were just talking about the star. I mean, you can heat, for example, you can heat the piece of something which you don't know what it is and think about the radiation which it starts emitting whenever it's hot enough. So all you need is just to pump energy into it. Now, it emits certain radiation, maybe visible light, maybe infrared light or something. Using the spectroscope, you can analyze exactly what elements are present in this particular piece of this substance, whatever the substance is and considering that we know which element produces which radiation we can judge about both the composition of this element and its temperature. That's how I can measure the temperature on a far away something just based on amount of radiation and type of frequency of radiation emitted by that particular source. So if you have, let's say, a lamp, I can direct the spectroscope on the lamp and it can actually give me the temperature and the composition. So this is, let's say, a tangent used in condensing lamps and it's temperature such and such. It can be done from the distance just based on the light which it emits. Okay, so I suggest you to read the notes for this lecture because every lecture on Unisor.com has notes which are basically like a textbook. And what's next? I think I left only one particular lecture about light. I will try to explain how the hologram are working. And that would be the end of this whole part related to waves. Okay, thank you very much and good luck.