1 00:00:00,120 --> 00:00:02,560 Speaker 1: Brain Stuff is sponsored by Harry's dot com. Get a 2 00:00:02,560 --> 00:00:04,840 Speaker 1: great shaving experience for a fraction of the price. The 3 00:00:04,920 --> 00:00:07,520 Speaker 1: quality of the shave is so important that Harry's purchased 4 00:00:07,520 --> 00:00:10,080 Speaker 1: the factory that makes their blades. Fifteen dollars gets you 5 00:00:10,119 --> 00:00:12,799 Speaker 1: a set that includes a handle, three blades, and shave cream. 6 00:00:12,840 --> 00:00:15,280 Speaker 1: Go to Harry's dot com use the code brain stuff 7 00:00:15,320 --> 00:00:18,720 Speaker 1: to say five dollars off your first purchase. Welcome to 8 00:00:18,800 --> 00:00:21,880 Speaker 1: brain Stuff from how stuff works dot com where smart 9 00:00:21,920 --> 00:00:29,280 Speaker 1: happens him Marshall brain. It's very common to see rainbow 10 00:00:29,360 --> 00:00:31,360 Speaker 1: patterns when you look at the surface of a c 11 00:00:31,560 --> 00:00:34,360 Speaker 1: D and also when you look at soap bubbles or 12 00:00:34,400 --> 00:00:38,000 Speaker 1: a thin film of oil floating on still water. Where 13 00:00:38,000 --> 00:00:41,559 Speaker 1: do these colors come from? All three of these rainbow 14 00:00:41,600 --> 00:00:45,320 Speaker 1: effects are created when light waves interact with each other. 15 00:00:45,800 --> 00:00:49,840 Speaker 1: It's known as constructive and destructive interference of the light 16 00:00:50,120 --> 00:00:54,240 Speaker 1: hitting thin surfaces. Think about a very thin film of 17 00:00:54,280 --> 00:00:58,160 Speaker 1: oil floating on water as an example. When white light 18 00:00:58,320 --> 00:01:01,560 Speaker 1: hits the film, most of it passes through the film, 19 00:01:01,600 --> 00:01:04,759 Speaker 1: but some is reflected off the top and bottom layers 20 00:01:04,800 --> 00:01:07,280 Speaker 1: of the film. In the same way. When you stand 21 00:01:07,280 --> 00:01:09,800 Speaker 1: in front of a window in your house, you can 22 00:01:09,920 --> 00:01:12,920 Speaker 1: see a reflected image in the window. Most of the 23 00:01:13,000 --> 00:01:15,600 Speaker 1: light is passing through the window and out of the house, 24 00:01:15,880 --> 00:01:19,120 Speaker 1: but some is reflected back at you. The light that 25 00:01:19,200 --> 00:01:22,040 Speaker 1: reflects off the top layer of a film of oil 26 00:01:22,200 --> 00:01:26,440 Speaker 1: travels slightly shorter distances than the light reflecting off the 27 00:01:26,440 --> 00:01:30,600 Speaker 1: bottom layer. If the film is very thin on the 28 00:01:30,720 --> 00:01:34,240 Speaker 1: order of the wavelength of light, then interference can occur. 29 00:01:35,000 --> 00:01:39,000 Speaker 1: Violet light has a wavelength of about four thousand angstroms, 30 00:01:39,000 --> 00:01:42,320 Speaker 1: and angstrom is a hundred millions of a centimeter, while 31 00:01:42,360 --> 00:01:45,319 Speaker 1: red light has a wavelength of about seven thousand, six 32 00:01:45,440 --> 00:01:49,680 Speaker 1: hundred angstroms, so we are talking about extremely thinned films. 33 00:01:50,240 --> 00:01:53,520 Speaker 1: If the film is just the right thickness, a red 34 00:01:53,640 --> 00:01:56,680 Speaker 1: light wave a side wave will bounce off the top 35 00:01:56,720 --> 00:01:59,880 Speaker 1: and bottom layers in perfect alignment, and the tubers a 36 00:02:00,320 --> 00:02:03,200 Speaker 1: sign ways will combine to double the amount of red 37 00:02:03,280 --> 00:02:07,480 Speaker 1: light scene, or they may reflect exactly out of phase 38 00:02:07,520 --> 00:02:11,359 Speaker 1: and the red light will be eliminated. Because specific colors 39 00:02:11,400 --> 00:02:14,600 Speaker 1: can be doubled or eliminated depending on the thickness of 40 00:02:14,639 --> 00:02:17,840 Speaker 1: the film, it changes the color of light and we 41 00:02:18,000 --> 00:02:22,320 Speaker 1: see colors like colors of the rainbow coming off the film. 42 00:02:22,360 --> 00:02:26,040 Speaker 1: On a CD, the surface is mirrored, so the rainbow 43 00:02:26,160 --> 00:02:29,640 Speaker 1: colors are much more intense. In a c D, the 44 00:02:29,720 --> 00:02:32,760 Speaker 1: angle that the CD is held at controls the colors 45 00:02:32,800 --> 00:02:35,960 Speaker 1: you see. The angle, along with the bumps on the 46 00:02:36,000 --> 00:02:39,480 Speaker 1: c D surface, controls the path difference and therefore the 47 00:02:39,520 --> 00:02:45,239 Speaker 1: colors you see. Do you have any ideas or suggestions 48 00:02:45,240 --> 00:02:48,200 Speaker 1: for this podcast? If so, please send me an email 49 00:02:48,240 --> 00:02:51,440 Speaker 1: at podcast at how stuff works dot com. For more 50 00:02:51,440 --> 00:02:53,680 Speaker 1: on this and thousands of other topics, go to how 51 00:02:53,720 --> 00:02:58,720 Speaker 1: stuff works dot com. Brain Stuff is sponsored by Harry's 52 00:02:58,760 --> 00:03:01,280 Speaker 1: dot com. Get a great evening experience for a fraction 53 00:03:01,320 --> 00:03:03,160 Speaker 1: of the price. The quality of the shave is so 54 00:03:03,200 --> 00:03:06,079 Speaker 1: important that Harry's purchased the factory that makes their blades. 55 00:03:06,120 --> 00:03:08,400 Speaker 1: Fifteen dollars gets you a set that includes a handle, 56 00:03:08,520 --> 00:03:11,000 Speaker 1: three blades, and shave cream. Go to Harry's dot com. 57 00:03:11,120 --> 00:03:13,520 Speaker 1: Use the code brain stuff to save five dollars off 58 00:03:13,520 --> 00:03:14,359 Speaker 1: your first purchase.