Lecture26_Kim

Lecture26_Kim - Lecture 26-1 Chapter 33 Interference and...

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Lecture 26-1 Coherence When the difference in phase between two (or more) waves remains constant (i.e., time-independent), the waves are said to be (perfectly) coherent . - laser light and light transmitted through a small aperture are coherent. - light from a light bulb and sun light over some area are in coherent. Geometric optics is a limit of the (general) optics where wave effects such as interference and diffraction are negligible. Wave optics (sometimes also called physical optics ) - wave effects play important roles. Geometric Optics vs Wave Optics Chapter 33 Interference and Diffraction
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Lecture 26-2 Wave Optics Derivation of Snell’s Law from Huygens’s Principle (1) As the wave moves into the medium, a Huygens wavelet at point e will expand to pass through point c , at a distance of 1 from point e . The time interval for that is 1 / v 1 . In the same time, a wavelet at point h will expand to pass through g , at velocity v 2 and with wave length 2 . e h c g 12 t vv    11 22 v v
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Lecture 26-3 Derivation of Snell’s Law from Huygens’s Principle (2) We can see that Solving for x we get Remembering that n = c / v we get Which is Snell’s Law! 12 sin and sin xx    1 1 1 2 2 2 sin sin v v  1 1 1 2 1 1 2 2 2 2 2 1 sin / or sin sin sin / v c n n nn v c n n h e c g [hec] [hcg]
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Lecture 26-4 Light Traveling in an Optical Medium (1) We have seen that the wavelength of light changes when traveling in an optical medium with index of refraction greater than one Taking with case 1 as a vacuum and case 2 as a medium with index of refraction n, we have found out that we can write Remembering that v = f we can write the frequency f n of light traveling in a medium as So the frequency does not change ! n v cn   / ( / ) n n vc f v v c f 12 t vv   n ff
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Lecture 26-5 Light Traveling in an Optical Medium (2) So the frequency of light traveling in an optical medium with n > 1 is the same as the frequency of that light traveling in vacuum We perceive color by frequency rather than wavelength Thus placing an object under water does not change our perception of the color of the object Easy to demonstrate: take a colored object and put it in a jar of water. Water has index of refraction n = 1.33. The object appears to have the same color under water as in air
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Lecture 26-6 Blocks of two different transparent materials are sitting in air and have identical light rays of single wavelength incident on them at the same angle. Examining the figure, what can you say about the speed of light in these two blocks? a) The speed of light is the same in both blocks. b) The speed of light is greater in the block on the left.
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Lecture26_Kim - Lecture 26-1 Chapter 33 Interference and...

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