Lecture22_Kim

# Lecture22_Kim - Lecture 22-1 The Speed of Light Speed of...

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Lecture 22-1 The Speed of Light Classic experiments to measure the speed of light: Galileo ( lantern and shutter ) Römer ( eclipses of Io behind Jupiter, 1675 ) Fizeau ( toothed wheel, 1849 ) Foucault ( plane rotating mirror, ~1850 ) Michelson ( octagonal rotating mirror, 1980 ) Michelson and Morley ( interferometer, 1887 ) 299,792,458 / c m s Speed of light is not infinite! Speed of light is not dependent on the motion of source/observer ( no fixed “ ether ”)

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Lecture 22-2 Huygens’s Principle Each point on a primary wavefront serves as the source of spherical secondary wavelets that advance with a speed and frequency equal to those of the primary wave. The primary wavefront at some later time is the envelope of these wavelets. t 1 t 2 t 3 t 1 t 2 t 3 points of given phase wavelet
Lecture 22-3 Reflection from Huygens’s Principle '' ABB BAP   11 '   Law of Reflection A reflected ray lies in the plane of incidence The angle of reflection is equal to the angle of incidence 1 1 1    AB PB ct 

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Lecture 22-4 Fermat’s Principle The path taken by light traveling from one point to another is such that the time of travel is a minimum . path: geometric ray is assumed for light. minimum time shortest path length reflection refraction
Lecture 22-5 Refraction = Transmission incident ray reflected ray refracted ray Medium 1 Medium 2 When light encounters an interface between different media, it can generally both reflect and refract . (This speed can even depend on wavelength.) Light can travel through matter medium as well as free space (vacuum). Inside matter, the speed of light v in the medium is generally less than c .

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## This note was uploaded on 12/07/2011 for the course PHYS 241 taught by Professor Wei during the Fall '08 term at Purdue.

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Lecture22_Kim - Lecture 22-1 The Speed of Light Speed of...

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