1 00:00:02,370 --> 00:00:04,880 Hello everyone. I'm Charles Clark. 2 00:00:04,880 --> 00:00:08,774 And I'm going to conduct some lectures on practical use of quantum mechanics to 3 00:00:08,774 --> 00:00:14,060 solve some real physics problems. The very interesting type. 4 00:00:14,060 --> 00:00:17,232 These are some of the most important problems in the early days of quantum 5 00:00:17,232 --> 00:00:21,880 physics, which led to the understanding of the structure of atoms. 6 00:00:21,880 --> 00:00:26,610 In enough detail to make possible number of applications that are very important. 7 00:00:26,610 --> 00:00:30,898 For example the development of the laser and it's a subject that was not imp-, 8 00:00:30,898 --> 00:00:34,994 important not only in the early days but it's a very vibrant field of research 9 00:00:34,994 --> 00:00:39,996 today. Since 1997, about 11 Nobel prizes in 10 00:00:39,996 --> 00:00:46,852 physics have been awarded. For innovative use of the interaction of 11 00:00:46,852 --> 00:00:52,442 light with atoms to do things like con, create ultra controlled ultra cold 12 00:00:52,442 --> 00:00:57,828 matter. develop new optical frequency standards, 13 00:00:57,828 --> 00:01:00,820 and the like. So it's a very vibrant field of research. 14 00:01:00,820 --> 00:01:05,120 And I hope these lectures will give you some sense of the excitement. 15 00:01:05,120 --> 00:01:08,970 And ma, and an impression of how you could actually approach it yourself. 16 00:01:12,150 --> 00:01:16,502 Now this is a fairly field with a lot of material in it, and I've only time to 17 00:01:16,502 --> 00:01:21,294 give you a brief introduction. So, let, let me just draw to your 18 00:01:21,294 --> 00:01:24,642 attention the fact that we have a page accessible along the main page of the 19 00:01:24,642 --> 00:01:30,267 website, Additional Materials. And we've put in a selection of original 20 00:01:30,267 --> 00:01:33,925 scientific literature with commentary there on various aspects that are 21 00:01:33,925 --> 00:01:37,222 important. So the things that are going to be talked 22 00:01:37,222 --> 00:01:40,342 about in detail in the first set of lectures by me are the Bore model of the 23 00:01:40,342 --> 00:01:43,772 atom. Not necessarily in this order the 24 00:01:43,772 --> 00:01:46,764 discovery of deuterium, fascinating story of which there's both a detailed and a 25 00:01:46,764 --> 00:01:50,480 sort of a simplified account. Recommend you look at. 26 00:01:50,480 --> 00:01:55,290 the, the green laser pointer and the photoelectric effect. 27 00:01:55,290 --> 00:01:59,700 Well, come to think of it, and the Young's Double Slit experiment. 28 00:01:59,700 --> 00:02:04,220 So, there's a very, couple introductory paragraphs in each one of these. 29 00:02:04,220 --> 00:02:06,728 if you find something that interests you in the lecture, I suggest you take a 30 00:02:06,728 --> 00:02:10,565 look. In fact the homework will require that 31 00:02:10,565 --> 00:02:15,237 you actually, read part of Einstein's original paper, on the photoelectric 32 00:02:15,237 --> 00:02:18,850 effect. It's, it's an awesome paper. 33 00:02:18,850 --> 00:02:21,937 And you have a choice of reading it in the, German original, which we provide 34 00:02:21,937 --> 00:02:25,171 you, or in the English translation that is available we give you a link to the 35 00:02:25,171 --> 00:02:31,970 English translation. At Wikimedia. 36 00:02:31,970 --> 00:02:34,230 Okay, let's begin talking about the world. 37 00:02:35,450 --> 00:02:38,790 Here's a happy scene. I'm sure you've all felt like this at 38 00:02:38,790 --> 00:02:43,011 some time, you're walking along and a very clear day, all of a sudden you see a 39 00:02:43,011 --> 00:02:51,893 beautiful rainbow. Now the world is full of colors. 40 00:02:51,893 --> 00:03:03,700 And the one's first impression is that the sun is a sort of a pure white light. 41 00:03:03,700 --> 00:03:06,850 It's a very natural color. It seems to display things. 42 00:03:08,140 --> 00:03:11,122 In some optimal way for us. They often like to inspect an object by 43 00:03:11,122 --> 00:03:14,910 taking it out in the open sunlight and seeing what it looks like. 44 00:03:14,910 --> 00:03:20,580 So the original impression of humanity is that the sun was the source of all light. 45 00:03:20,580 --> 00:03:23,742 Indeed, you know, maybe fires would produce something, but for a long time 46 00:03:23,742 --> 00:03:28,950 there were no artificial lights. And occasionally it would show, these 47 00:03:28,950 --> 00:03:33,706 effects where you would see in the otherwise clear sky a spectrum that 48 00:03:33,706 --> 00:03:40,433 seemed to contain all the possible colors of human experience. 49 00:03:40,433 --> 00:03:46,243 Now here's another example using a fairly natural material, a piece of glass, where 50 00:03:46,243 --> 00:03:52,053 we see a case where a white light comes in and then a number of other colors, red 51 00:03:52,053 --> 00:03:58,054 blue, are emitted. Basically, the white light is spread, 52 00:03:58,054 --> 00:04:01,570 somehow changed into a spread out system of colors. 53 00:04:01,570 --> 00:04:04,790 Now, this is a phenomenon that was known in antiquity. 54 00:04:04,790 --> 00:04:10,010 And people then seemed to think that there was something about the. 55 00:04:10,010 --> 00:04:14,618 The shape of the prism or the qualities of the glass that impressed different 56 00:04:14,618 --> 00:04:20,840 colors on sunlight, which was otherwise a clear white light. 57 00:04:20,840 --> 00:04:23,570 But Newton showed that this was not the case, and that in fact that sunlight was 58 00:04:23,570 --> 00:04:26,919 a mixture of colors. And it's by one of these experiments that 59 00:04:26,919 --> 00:04:29,910 when you hear about it you think it's so obvious. 60 00:04:29,910 --> 00:04:34,770 What he did was, he took sunlight, and put it through a prism. 61 00:04:34,770 --> 00:04:38,900 But then he, he took some of the separated light, a light of a pure color, 62 00:04:38,900 --> 00:04:43,310 and put it into a second prism, and he saw there that no further separation of 63 00:04:43,310 --> 00:04:49,716 the colors occurred. So the natural way of interpreting that 64 00:04:49,716 --> 00:04:53,808 result, is that white light is a, is for some reason a mixture of all these colors 65 00:04:53,808 --> 00:04:58,726 put together. And what the prism does, is separate them 66 00:04:58,726 --> 00:05:01,080 out. we call this the dispersion of the 67 00:05:01,080 --> 00:05:05,370 colors. by the by the prism. 68 00:05:06,830 --> 00:05:10,490 Now, from today's stand point we know that color is an index of the light's 69 00:05:10,490 --> 00:05:12,321 wavelength. Lambda. 70 00:05:12,321 --> 00:05:13,608 Conventional designation for the wavelength of light. 71 00:05:13,608 --> 00:05:15,144 And, there's a famous equation, which you're going to get some more practice 72 00:05:15,144 --> 00:05:23,551 with. The relationship between frequency, Nu, 73 00:05:23,551 --> 00:05:32,036 and wavelength Lambda. So, Nu is equal to c over Lambda, where C 74 00:05:32,036 --> 00:05:36,301 is the speed of light. Oh, so C has the units of meters per 75 00:05:36,301 --> 00:05:41,770 second, or length divided by time, Lambda has the units of length. 76 00:05:41,770 --> 00:05:45,466 And what is a wavelength, a wavelength is a wave motion. 77 00:05:46,660 --> 00:05:52,575 The wave length is the distance over which the wave motion begins to repeat 78 00:05:52,575 --> 00:06:00,071 itself and C is the speed of light. So what we as you're going to see there 79 00:06:00,071 --> 00:06:06,745 is a conventional way of designating the characteristics of light in the optical 80 00:06:06,745 --> 00:06:14,950 region of the spectrum and I'll explain to you why that is. 81 00:06:14,950 --> 00:06:18,835 Now, here's a little inverse example of what you saw in the prism. 82 00:06:18,835 --> 00:06:25,066 A very elegant and interesting demonstration made by Alexander Albrecht 83 00:06:25,066 --> 00:06:31,666 of the University of New Mexico. This is a prize winning photograph from 84 00:06:31,666 --> 00:06:36,730 the membership magazine of the Optical Society of America, December 2012. 85 00:06:36,730 --> 00:06:42,058 So, what is done here is, there are these three three pipes of water, there's water 86 00:06:42,058 --> 00:06:46,738 streaming into a bowl and then a laser is put into the into the pipe and the laser 87 00:06:46,738 --> 00:06:54,349 beam is entrained in the water. This is a demonstration you may have seen 88 00:06:54,349 --> 00:06:59,508 before, but what's done here is a red, green and a violet laser are used to, put 89 00:06:59,508 --> 00:07:06,748 the light of separate colors in the bowl. Then the light scatters around, and so 90 00:07:06,748 --> 00:07:11,228 what you see coming out from your eye is, it's a, it's a scattered combination 91 00:07:11,228 --> 00:07:17,828 containing, you know, more or less the same quantity of red, green and violet. 92 00:07:17,828 --> 00:07:21,400 So that gives a white appearance, very nice. 93 00:07:21,400 --> 00:07:26,358 Now the these three lasers are of a common type and we're going to, they're 94 00:07:26,358 --> 00:07:32,664 all actually available as laser pointers. And, and, they light in this region of 95 00:07:32,664 --> 00:07:36,024 wavelengths is available as a very inexpensive laser pointer, costing 96 00:07:36,024 --> 00:07:42,102 between five and ten American dollars. And so we are going to use, throughout 97 00:07:42,102 --> 00:07:46,782 these lectures, these three lasers as sort of standard reference lasers, for 98 00:07:46,782 --> 00:07:53,942 the for the discussion of the course. So the red laser, at a wavelength of 650 99 00:07:53,942 --> 00:07:59,704 nanometers, a green laser, at a wavelength of 532 nanometers, this is the 100 00:07:59,704 --> 00:08:07,142 famous diode pump solid state. The wavelength produced by diode pump 101 00:08:07,142 --> 00:08:10,080 solid state architecture that's used in the green laser pointer. 102 00:08:10,080 --> 00:08:13,618 And then finally, the wavelength of four or five nanometers, which is the 103 00:08:13,618 --> 00:08:21,842 wavelength. Sorry, wavelength of the blue, using the 104 00:08:21,842 --> 00:08:26,587 blu-ray laser, so if you have a blu-ray system or a Playstation at home, you are 105 00:08:26,587 --> 00:08:33,819 the already the proud owner of one of these four or five nanometer lasers. 106 00:08:33,819 --> 00:08:39,846 Okay, and so now as an introduction to. The application of some of these basic 107 00:08:39,846 --> 00:08:43,450 concepts of optics. I mean, I'll give you a little inline 108 00:08:43,450 --> 00:08:48,142 quiz, that has to do, with the properties of one of my favorites, which is the the 109 00:08:48,142 --> 00:08:54,324 green laser pointer. Okay, I hope that some of you found that, 110 00:08:54,324 --> 00:08:58,589 example, relatively easy. I hope all of you found it at least 111 00:08:58,589 --> 00:09:03,067 interesting. The idea that you can use a passive 112 00:09:03,067 --> 00:09:09,663 crystal to change the color of light is something that's only become possible 113 00:09:09,663 --> 00:09:17,280 well since the development of the laser in the 1960's. 114 00:09:17,280 --> 00:09:21,970 And to learn a little bit more about that I recommend this paper on the green laser 115 00:09:21,970 --> 00:09:26,526 pointer it's written, I hope in a fairly accessible way it's not highly technical 116 00:09:26,526 --> 00:09:30,814 and does provide a simplified description of the operation device if you're 117 00:09:30,814 --> 00:09:36,573 interested. Now one thing that you're going to have 118 00:09:36,573 --> 00:09:40,721 to do if you want to be a successful physicist or a successful scientist any 119 00:09:40,721 --> 00:09:45,155 time, is to lose your sense of complacency. 120 00:09:45,155 --> 00:09:51,100 When you wake up everyday, you see the white light of the sun. 121 00:09:51,100 --> 00:09:55,380 You see the rainbow from time to time, you see the same colors over and over. 122 00:09:55,380 --> 00:10:01,280 You might think, what else is there? Well, the answer is revealed. 123 00:10:01,280 --> 00:10:03,860 By being able to look where no one has looked before. 124 00:10:03,860 --> 00:10:07,435 And that's really the, why we do quantum physics today, is to try to understand 125 00:10:07,435 --> 00:10:11,926 things at a deeper level. And here is an example of how that type 126 00:10:11,926 --> 00:10:15,398 of deep understanding, made on an observation by a man who, you know, alone 127 00:10:15,398 --> 00:10:19,660 in the world at the time, had the capability. 128 00:10:19,660 --> 00:10:24,610 Of making those detailed observations made a tremendous change in science and 129 00:10:24,610 --> 00:10:29,110 history, and that man was Joseph von Fraunhofer, one of the most skilled 130 00:10:29,110 --> 00:10:36,351 optical physicists of his day. He was a specialist in making various 131 00:10:36,351 --> 00:10:41,688 types of optical glass that had very high dispersion, so he could make prisms. 132 00:10:41,688 --> 00:10:46,028 That would separate out light to greater the different colors of light to a 133 00:10:46,028 --> 00:10:50,508 greater degree than any one else, and here is a paper from his publication and 134 00:10:50,508 --> 00:10:54,568 in fact that you can acquire that publication through our additional 135 00:10:54,568 --> 00:10:59,328 materials uh,document of course its written in German actually rather an old 136 00:10:59,328 --> 00:11:06,827 fashioned type of German. Maybe some students in the German 137 00:11:06,827 --> 00:11:13,022 discussion group can comment upon that. But this is a drawing produced by 138 00:11:13,022 --> 00:11:18,440 Fraunhofer of what he saw when he looked at the light of the sun using a highly 139 00:11:18,440 --> 00:11:26,210 dispersive prism. He saw dark lines in the spectrum. 140 00:11:26,210 --> 00:11:30,490 So, imbedded in this rainbow, there were patches of darkness. 141 00:11:30,490 --> 00:11:34,736 Hundreds of them. Now, well, might you ask, how did he know 142 00:11:34,736 --> 00:11:39,056 that those were patches in the light of the sun itself, rather than maybe 143 00:11:39,056 --> 00:11:44,676 something in the earth's air, that would be blocking? 144 00:11:44,676 --> 00:11:48,230 would, would be doing something in the sunlight. 145 00:11:48,230 --> 00:11:55,190 Well it's a good question, and Fraunhofer answered it, at least in part. 146 00:11:55,190 --> 00:11:58,622 By also looking at the light from other stars, in particular the star Sirius, is 147 00:11:58,622 --> 00:12:03,841 one that he reports. And he saw other dark lines there, but 148 00:12:03,841 --> 00:12:09,760 not necessarily exactly the same dark lines that were in the sun. 149 00:12:09,760 --> 00:12:13,418 So, in other words, at least a number of these dark lines are definitely 150 00:12:13,418 --> 00:12:19,272 associated with the light of the sun. Now, you know there's been many ideas of 151 00:12:19,272 --> 00:12:25,280 color and of the nature of the sun and everything throughout history. 152 00:12:25,280 --> 00:12:28,702 But I don't know of a case where someone's just sat down and said, well, I 153 00:12:28,702 --> 00:12:32,182 bet there's a whole bunch of dark lines in the light of the sun that we just 154 00:12:32,182 --> 00:12:36,990 haven't seen yet. And maybe someday, someone's going to 155 00:12:36,990 --> 00:12:40,400 invent some optical device that will allow them to be revealed. 156 00:12:41,580 --> 00:12:44,103 So now let's take another, we'll take a look. 157 00:12:44,103 --> 00:12:50,430 At, a more modern observation, the same thing. 158 00:12:50,430 --> 00:12:54,910 Behold the crown of the great king of the solar system, the sun. 159 00:12:54,910 --> 00:12:58,430 Here's a wonderful image, that's a spectrum of the sun seen at high 160 00:12:58,430 --> 00:13:02,974 resolution produced at the, the, National Optical Astronomical Observatory in 161 00:13:02,974 --> 00:13:09,160 Tucson, Arizona. And let me just describe to you how this 162 00:13:09,160 --> 00:13:14,170 was taken. Let's say that you're looking at the 163 00:13:14,170 --> 00:13:18,794 rainbow in the skies. So here's the red bow that's above and 164 00:13:18,794 --> 00:13:24,716 then down at the bottom, there's a violet one, and then, from violet, we go to 165 00:13:24,716 --> 00:13:32,950 blue, I guess it is. Then to green. 166 00:13:32,950 --> 00:13:39,010 And to yellow. And, and orange, and so on back up to the 167 00:13:39,010 --> 00:13:41,729 red. So here's a, here's a crude drawing of 168 00:13:41,729 --> 00:13:45,730 the rainbow. So you, if you, if you had a picture of 169 00:13:45,730 --> 00:13:51,988 that. And then you, cut out, a little thin 170 00:13:51,988 --> 00:14:00,280 strip like that, now you take, this thin strip. 171 00:14:04,780 --> 00:14:10,066 Orient it here. So for example this could be the red, the 172 00:14:10,066 --> 00:14:18,250 sort of, the red patch. And then down here this would be the 173 00:14:18,250 --> 00:14:25,122 violet. Then what you do is that you, you cut out 174 00:14:25,122 --> 00:14:32,426 50 of these strips, like this and then what you do is you stretch. 175 00:14:32,426 --> 00:14:38,536 Stretch each one of these out to expand the region so this enables you, in other 176 00:14:38,536 --> 00:14:47,895 words if you were to take these 50 strips there 50 strips stacked vertically here. 177 00:14:47,895 --> 00:14:53,975 And if you lay them end to end you would see the rainbow but with the resolution 178 00:14:53,975 --> 00:14:59,849 that allows you to see all this fine detail. 179 00:14:59,849 --> 00:15:06,404 Now for your guidance I have positioned some of our reference lasers near where 180 00:15:06,404 --> 00:15:13,850 they would be in this spectrum. Here's 650 nanometers, 532. 181 00:15:13,850 --> 00:15:19,604 The blu-ray laser. And now what this indicates is that, the 182 00:15:19,604 --> 00:15:25,680 wavelength is I'll, I'll draw it on this side. 183 00:15:28,790 --> 00:15:32,816 The wavelength is increasing within a strip as you go from the right to the 184 00:15:32,816 --> 00:15:38,830 left because this is short wavelength, and you're going backwards, you see. 185 00:15:38,830 --> 00:15:40,790 So you're, you're increasing the wavelength. 186 00:15:41,919 --> 00:15:49,910 And then it's also increasing as you go from one strip to the next. 187 00:15:51,240 --> 00:15:54,295 Is that clear? Well you're going to now get an 188 00:15:54,295 --> 00:15:58,760 opportunity to see whether you grasp the concept. 189 00:15:58,760 --> 00:16:03,316 Okay again I hope that some of you got the, material on the online quiz and, and 190 00:16:03,316 --> 00:16:09,384 everyone found at least. Interesting enough to, to think about the 191 00:16:09,384 --> 00:16:13,864 problem that's not it's not complicated. A heavy map but its a good experience in 192 00:16:13,864 --> 00:16:17,400 actually you know looking at the results of experimental data and understanding 193 00:16:17,400 --> 00:16:20,936 very clearly what that representation means because these things aren't always 194 00:16:20,936 --> 00:16:25,686 obvious. Okay, that's it for today, and I will, 195 00:16:25,686 --> 00:16:29,964 well, that's it for this lecture. We'll resume and talk more about 196 00:16:29,964 --> 00:16:32,520 interference, and attraction.