Physics for Scientists and Engineers 8ed - ch35 - PowerPoint Slides

Physics for Scientists and Engineers 8ed - ch35 - PowerPoint Slides

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Unformatted text preview: Chapter 35 The Nature of Light and the Laws of Geometric Optics The Nature of Light Before the beginning of the nineteenth century, light was considered to be a stream of particles The particles were either emitted by the object being viewed or emanated from the eyes of the viewer Newton was the chief architect of the particle theory of light He believed the particles left the object and stimulated the sense of sight upon entering the eyes Nature of Light Alternative View Christian Huygens argued that light might be some sort of a wave motion Thomas Young (in 1801) provided the first clear demonstration of the wave nature of light He showed that light rays interfere with each other Such behavior could not be explained by particles More Confirmation of Wave Nature During the nineteenth century, other developments led to the general acceptance of the wave theory of light Maxwell asserted that light was a form of high-frequency electromagnetic wave Hertz confirmed Maxwells predictions Particle Nature Some experiments could not be explained by the wave nature of light The photoelectric effect was a major phenomenon not explained by waves When light strikes a metal surface, electrons are sometimes ejected from the surface The kinetic energy of the ejected electron is independent of the frequency of the light Particle Nature, cont. Einstein (in 1905) proposed an explanation of the photoelectric effect that used the idea of quantization The quantization model assumes that the energy of a light wave is present in particles called photons E = h h is Plancks Constant and = 6.63 x 10-34 J . s Dual Nature of Light In view of these developments, light must be regarded as having a dual nature Light exhibits the characteristics of a wave in some situations and the characteristics of a particle in other situations Measurements of the Speed of Light Since light travels at a very high speed, early attempts to measure its speed were unsuccessful Remember c = 3.00 x 10 8 m/s Galileo tried by using two observers separated by about 10 km The reaction time of the observers was more than the transit time of the light Measurement of the Speed of Light Roemers Method Ole Roemer (1675) used astronomical observations to estimate the speed of light He used the period of revolution of Io, a moon of Jupiter, as Jupiter revolved around the sun Roemers Method, cont. The periods of revolution were longer when the Earth was receding from Jupiter Shorter when the Earth was approaching Using Roemers data, Huygens estimated the lower limit of the speed of light to be 2.3 x 10 8 m/s This was important because it demonstrated that light has a finite speed as well as giving an estimate of that speed Measurements of the Speed of Light Fizeaus Method This was the first successful method for measuring the speed of light by means of a...
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This note was uploaded on 05/22/2010 for the course PHYS 2326 taught by Professor Staff during the Summer '08 term at HCCS.

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Physics for Scientists and Engineers 8ed - ch35 - PowerPoint Slides

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