1 00:00:00,090 --> 00:00:02,490 The following content is provided under a Creative 2 00:00:02,490 --> 00:00:04,030 Commons license. 3 00:00:04,030 --> 00:00:06,330 Your support will help MIT OpenCourseWare 4 00:00:06,330 --> 00:00:10,720 continue to offer high quality educational resources for free. 5 00:00:10,720 --> 00:00:13,320 To make a donation or view additional materials 6 00:00:13,320 --> 00:00:17,280 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,280 --> 00:00:20,460 at ocw.mit.edu. 8 00:00:20,460 --> 00:00:23,550 MARK HARTMAN: This exit sign. 9 00:00:23,550 --> 00:00:25,890 So those are our important observations. 10 00:00:25,890 --> 00:00:26,932 Let me introduce to you-- 11 00:00:26,932 --> 00:00:29,431 I'm going to tell you how we're going to change the particle 12 00:00:29,431 --> 00:00:30,160 model of light. 13 00:00:30,160 --> 00:00:31,830 We're going to add this in. 14 00:00:31,830 --> 00:00:35,745 Remember, before we had-- 15 00:00:35,745 --> 00:00:37,650 this is what I want. 16 00:00:37,650 --> 00:00:41,130 Before, we said that light is a bunch of particles 17 00:00:41,130 --> 00:00:44,580 that are traveling outward from a source at all directions 18 00:00:44,580 --> 00:00:48,970 in straight lines moving at the same speed. 19 00:00:48,970 --> 00:00:51,030 So what I want you to do now, is we're 20 00:00:51,030 --> 00:00:58,740 going to say addition of color to particle model. 21 00:01:02,866 --> 00:01:04,760 Remember, we also said that those particles 22 00:01:04,760 --> 00:01:06,930 we're going to call photons. 23 00:01:06,930 --> 00:01:18,090 Now, we're going to say each photon can be 24 00:01:18,090 --> 00:01:24,520 a different amount of energy. 25 00:01:30,680 --> 00:01:34,520 Before, we said those photons that were traveling outward 26 00:01:34,520 --> 00:01:36,516 were particles of energy. 27 00:01:36,516 --> 00:01:38,390 We're going to refine our model a little bit. 28 00:01:38,390 --> 00:01:39,860 We're going to say each photon can be 29 00:01:39,860 --> 00:01:41,068 a different amount of energy. 30 00:01:41,068 --> 00:01:44,120 Not all photons have to be bundles 31 00:01:44,120 --> 00:01:45,350 of the same amount of energy. 32 00:01:50,180 --> 00:01:54,350 Remember, a photon is our particle of energy. 33 00:01:54,350 --> 00:02:06,910 And we're just going to say that humans experience photons 34 00:02:06,910 --> 00:02:18,670 with different energies as different colors. 35 00:02:27,840 --> 00:02:31,080 Humans experience photons with different energies 36 00:02:31,080 --> 00:02:33,270 as different colors. 37 00:02:33,270 --> 00:02:37,310 So color is a word that we've made up 38 00:02:37,310 --> 00:02:40,380 to talk about how our brain interprets 39 00:02:40,380 --> 00:02:41,745 photons of different energies. 40 00:02:44,890 --> 00:02:48,400 So if I again draw my model, here's 41 00:02:48,400 --> 00:02:50,005 my light bulb or light source. 42 00:02:53,410 --> 00:02:55,390 Before we just said that there were photons, 43 00:02:55,390 --> 00:02:58,460 these particles of energy coming out in all directions. 44 00:02:58,460 --> 00:03:00,850 Now we're going to say each photon is 45 00:03:00,850 --> 00:03:03,020 a different amount of energy. 46 00:03:03,020 --> 00:03:07,840 So we're going to say there are some photons that 47 00:03:07,840 --> 00:03:12,550 have an amount of energy that when those photons are received 48 00:03:12,550 --> 00:03:17,780 by our eyes, we interpret them as the color blue. 49 00:03:17,780 --> 00:03:18,280 All right. 50 00:03:18,280 --> 00:03:29,010 So there are some blue photons, there are some green photons, 51 00:03:29,010 --> 00:03:33,880 and there are some red photons. 52 00:03:33,880 --> 00:03:40,220 Now, right now I'm just kind of telling you that red, green, 53 00:03:40,220 --> 00:03:46,720 and blue, but there's every possible imaginable color. 54 00:03:46,720 --> 00:03:50,250 Each one of these photons is a bundle of energy 55 00:03:50,250 --> 00:03:52,340 that's a different amount. 56 00:03:52,340 --> 00:03:57,910 For instance, red photons carry smaller amounts of energy; 57 00:03:57,910 --> 00:04:01,180 green photons carry larger amounts of energy; 58 00:04:01,180 --> 00:04:05,240 and blue photons carry even larger amounts of energy. 59 00:04:05,240 --> 00:04:09,250 So this is our addition of color to the particle model. 60 00:04:09,250 --> 00:04:10,900 So let's think about how we can use 61 00:04:10,900 --> 00:04:15,760 this to interpret or to build a model, not just of color 62 00:04:15,760 --> 00:04:21,189 in general, but let's build a model of how the filters work. 63 00:04:21,189 --> 00:04:23,230 So what I want you to do with your group for just 64 00:04:23,230 --> 00:04:28,450 a couple of minutes, I want you to think about 65 00:04:28,450 --> 00:04:38,290 how could I make a drawing that if I put a red filter here, 66 00:04:38,290 --> 00:04:40,480 red filter-- 67 00:04:40,480 --> 00:04:42,490 based on our observations here I want you 68 00:04:42,490 --> 00:04:46,990 guys to make a model of if we had 69 00:04:46,990 --> 00:04:50,800 a detector over on this side, which we're going to say 70 00:04:50,800 --> 00:04:56,500 is just our eye, what's going to happen 71 00:04:56,500 --> 00:05:05,766 if we look at this object, which is a light bulb, which puts out 72 00:05:05,766 --> 00:05:07,015 all of these different colors? 73 00:05:10,020 --> 00:05:16,826 What would we see over on this side based on the fact 74 00:05:16,826 --> 00:05:19,200 that there are photons of all different colors coming out 75 00:05:19,200 --> 00:05:19,510 of there? 76 00:05:19,510 --> 00:05:21,760 So just for a couple of minutes think with your group, 77 00:05:21,760 --> 00:05:23,970 how could you represent what's actually 78 00:05:23,970 --> 00:05:25,424 going to get over here? 79 00:05:25,424 --> 00:05:27,090 Bring a couple of ideas floating around. 80 00:05:27,090 --> 00:05:30,420 Does anybody want to come and volunteer 81 00:05:30,420 --> 00:05:32,380 to tell us what they think. 82 00:05:32,380 --> 00:05:33,350 Asith. 83 00:05:33,350 --> 00:05:33,850 Go ahead. 84 00:05:39,229 --> 00:05:40,696 ASITH: [INAUDIBLE]. 85 00:06:02,060 --> 00:06:04,170 MARK HARTMAN: OK. 86 00:06:04,170 --> 00:06:05,100 So that was great. 87 00:06:05,100 --> 00:06:08,460 Would somebody like to come and draw a picture of that? 88 00:06:08,460 --> 00:06:10,380 How could we represent this on our diagram? 89 00:06:15,280 --> 00:06:16,530 Somebody else from your group? 90 00:06:16,530 --> 00:06:18,114 Nicky, Island? 91 00:06:18,114 --> 00:06:19,410 STUDENT: I can try. 92 00:06:19,410 --> 00:06:20,280 MARK HARTMAN: Yeah. 93 00:06:20,280 --> 00:06:22,500 Try for it. 94 00:06:22,500 --> 00:06:26,140 So let's represents in our diagram here, 95 00:06:26,140 --> 00:06:29,311 which I know you guys don't have color to put in your notebooks, 96 00:06:29,311 --> 00:06:30,810 but maybe you have different shapes. 97 00:06:30,810 --> 00:06:32,190 You could represent the red, green, and the blue 98 00:06:32,190 --> 00:06:33,023 by different shapes. 99 00:07:00,761 --> 00:07:01,260 OK. 100 00:07:01,260 --> 00:07:04,920 So explain to us what you drew and why you drew it that way. 101 00:07:04,920 --> 00:07:10,088 STUDENT: The red light goes through the filter. 102 00:07:10,088 --> 00:07:11,300 So it goes through. 103 00:07:11,300 --> 00:07:12,100 You can see it. 104 00:07:12,100 --> 00:07:15,380 But the blue and the green light doesn't 105 00:07:15,380 --> 00:07:19,690 go through the filter as much, so we can't really see it. 106 00:07:19,690 --> 00:07:22,420 And it stops there. 107 00:07:22,420 --> 00:07:23,140 MARK HARTMAN: OK. 108 00:07:23,140 --> 00:07:23,950 That's great. 109 00:07:23,950 --> 00:07:26,150 This is a great representation, this 110 00:07:26,150 --> 00:07:28,560 is a great model of what filters do. 111 00:07:28,560 --> 00:07:31,600 If you have a red filter it lets the photons of red light 112 00:07:31,600 --> 00:07:35,960 through, just like when we looked at the exit sign 113 00:07:35,960 --> 00:07:37,960 we look at the exit sign through the red filter, 114 00:07:37,960 --> 00:07:39,325 it lets that red light through. 115 00:07:39,325 --> 00:07:45,480 But if you put a green filter up you can't see the red light. 116 00:07:45,480 --> 00:07:46,400 Why not, Jalen? 117 00:07:46,400 --> 00:07:51,340 JALEN: Because it blends in with the background. 118 00:07:51,340 --> 00:07:53,550 MARK HARTMAN: Well, it blends in with the background. 119 00:07:53,550 --> 00:07:54,620 But why? 120 00:07:54,620 --> 00:07:57,223 Why in terms of our particle model? 121 00:07:57,223 --> 00:08:01,500 JALEN: You can't see the red, that you 122 00:08:01,500 --> 00:08:04,760 can see like how it says exit. 123 00:08:04,760 --> 00:08:06,530 You can barely see it. 124 00:08:06,530 --> 00:08:10,550 MARK HARTMAN: You can't see the word exit 125 00:08:10,550 --> 00:08:13,775 because does the red light get through a blue filter? 126 00:08:13,775 --> 00:08:14,710 JALEN: No. 127 00:08:14,710 --> 00:08:15,820 MARK HARTMAN: No. 128 00:08:15,820 --> 00:08:19,410 So the blue filter only lets through blue light. 129 00:08:19,410 --> 00:08:21,590 So if you look at the red exit sign 130 00:08:21,590 --> 00:08:25,310 with blue and green filters, it's going to block the red 131 00:08:25,310 --> 00:08:27,740 and only let blue and green through. 132 00:08:27,740 --> 00:08:30,680 But since there's no blue light or no green light coming 133 00:08:30,680 --> 00:08:34,176 from the exit sign, you don't see anything. 134 00:08:34,176 --> 00:08:35,210 OK. 135 00:08:35,210 --> 00:08:37,880 So we've now built this model. 136 00:08:37,880 --> 00:08:46,640 Let's actually say this is a model of how filters work. 137 00:08:49,730 --> 00:09:01,560 So let's say they block all photons 138 00:09:01,560 --> 00:09:08,710 except the color of the filter. 139 00:09:13,520 --> 00:09:17,870 So are light and color two different things? 140 00:09:17,870 --> 00:09:19,400 No. 141 00:09:19,400 --> 00:09:22,310 Color is a property of light. 142 00:09:25,790 --> 00:09:32,060 Color is describing the energy of those different photons. 143 00:09:32,060 --> 00:09:35,240 It's not that color is a separate thing from light, 144 00:09:35,240 --> 00:09:38,910 but color is a property of light. 145 00:09:38,910 --> 00:09:43,640 So what we're going to do now is we're going to use this model. 146 00:09:43,640 --> 00:09:45,950 We took some observations, we developed 147 00:09:45,950 --> 00:09:48,500 a model of how this works. 148 00:09:48,500 --> 00:09:50,150 Let's test the model out. 149 00:09:50,150 --> 00:09:52,640 Let's make some predictions with this model, 150 00:09:52,640 --> 00:09:54,896 or at least your understanding. 151 00:09:54,896 --> 00:09:57,020 And if we make some predictions in a new situation, 152 00:09:57,020 --> 00:09:59,630 if it still works out, hey, that's great. 153 00:09:59,630 --> 00:10:01,460 Then our model works because we only 154 00:10:01,460 --> 00:10:04,520 did a couple of observations. 155 00:10:04,520 --> 00:10:06,980 Maybe this isn't the real way it works maybe it's 156 00:10:06,980 --> 00:10:09,890 not quite exactly like this. 157 00:10:09,890 --> 00:10:11,480 So we need to make some predictions 158 00:10:11,480 --> 00:10:13,450 based on this model. 159 00:10:13,450 --> 00:10:20,120 So Peter or Shaqib, could you turn on our projector here 160 00:10:20,120 --> 00:10:22,290 without any filters? 161 00:10:22,290 --> 00:10:25,250 So a lot of you probably have seen this before. 162 00:10:25,250 --> 00:10:28,460 What we have on the front of this-- 163 00:10:28,460 --> 00:10:30,290 go ahead and turn it on just so we can see. 164 00:10:30,290 --> 00:10:31,790 On the front of this projector we're 165 00:10:31,790 --> 00:10:35,070 just projecting a line of straight, plain old white 166 00:10:35,070 --> 00:10:35,570 light. 167 00:10:35,570 --> 00:10:37,510 We have a light bulb down there. 168 00:10:37,510 --> 00:10:41,630 The light photons are traveling up, being focused 169 00:10:41,630 --> 00:10:42,950 through this lens up here. 170 00:10:42,950 --> 00:10:44,840 And then it's actually making an image 171 00:10:44,840 --> 00:10:49,460 of what's on the top of this overhead projector. 172 00:10:49,460 --> 00:10:52,180 Here we have a diffraction grating. 173 00:10:52,180 --> 00:10:56,960 A diffraction grating is kind of like a prism, in that it takes 174 00:10:56,960 --> 00:11:02,450 that light and it takes white light, which 175 00:11:02,450 --> 00:11:07,760 is all of those different colors of photons traveling together 176 00:11:07,760 --> 00:11:12,380 and it spreads them out, so that on this side over here 177 00:11:12,380 --> 00:11:15,560 only the red photons go this direction, 178 00:11:15,560 --> 00:11:18,200 only the green photons go in the middle, 179 00:11:18,200 --> 00:11:20,690 and only the blue photons and purple photons 180 00:11:20,690 --> 00:11:23,162 go off to the left. 181 00:11:23,162 --> 00:11:25,370 So what we're doing is we're taking a stream of light 182 00:11:25,370 --> 00:11:26,930 and we're breaking it up depending 183 00:11:26,930 --> 00:11:31,070 on what the energy the photons is, with the energy 184 00:11:31,070 --> 00:11:33,830 of the photons are. 185 00:11:33,830 --> 00:11:39,040 So what I want you to do with your group, 186 00:11:39,040 --> 00:11:42,700 I have a red filter here just like the one that you have, 187 00:11:42,700 --> 00:11:46,900 if I put this red filter in front of this diffraction 188 00:11:46,900 --> 00:11:51,970 grating, I want you to predict what we're going to see on, 189 00:11:51,970 --> 00:11:55,460 let's just say on this side, of the board. 190 00:11:55,460 --> 00:11:57,160 It actually splits it up in two ways. 191 00:11:57,160 --> 00:12:02,230 So we've got the same rainbow on both sides, the same spectrum. 192 00:12:02,230 --> 00:12:03,400 So what I want you to do-- 193 00:12:06,070 --> 00:12:08,020 can you guys grab the colored pencils? 194 00:12:08,020 --> 00:12:11,560 So we have covered pencils, and I 195 00:12:11,560 --> 00:12:14,800 want you to actually draw in your notebook, 196 00:12:14,800 --> 00:12:16,720 I want you to predict what you're 197 00:12:16,720 --> 00:12:19,330 going to see if we take the red filter 198 00:12:19,330 --> 00:12:20,500 and we put it right there. 199 00:12:20,500 --> 00:12:27,760 What's going to happen over on this side of the board? 200 00:12:27,760 --> 00:12:31,500 So I want you to predict based on this idea that-- 201 00:12:31,500 --> 00:12:41,040 now, if we put this on, move it over a little bit, 202 00:12:41,040 --> 00:12:41,899 that's what you see. 203 00:12:41,899 --> 00:12:43,690 So let's turn the lights down a little bit. 204 00:12:49,490 --> 00:12:51,280 Let's go ahead and turn them off. 205 00:12:51,280 --> 00:12:53,900 So this is normal. 206 00:12:53,900 --> 00:12:56,370 That's with the red filter. 207 00:12:56,370 --> 00:12:59,950 So if you want to come up and look at it up close and come 208 00:12:59,950 --> 00:13:03,520 flip this up and then flip it back down. 209 00:13:03,520 --> 00:13:04,120 OK. 210 00:13:04,120 --> 00:13:05,620 So come up and look, then I want you 211 00:13:05,620 --> 00:13:09,030 to represent what you're seeing here on your paper. 212 00:13:11,710 --> 00:13:14,920 So that's regular. 213 00:13:14,920 --> 00:13:17,780 That's with the red filter. 214 00:13:17,780 --> 00:13:20,330 So I want you to represent that again in another drawing. 215 00:13:20,330 --> 00:13:21,790 And then I want you to think about, 216 00:13:21,790 --> 00:13:26,120 how is your prediction different from that? 217 00:13:26,120 --> 00:13:29,030 And then I want you to discuss with your group 218 00:13:29,030 --> 00:13:32,155 why you think that's different. 219 00:13:32,155 --> 00:13:33,530 Discuss with your original group. 220 00:13:36,860 --> 00:13:40,370 So this is the original and then that's 221 00:13:40,370 --> 00:13:42,490 what you see with the filter.