lecture 2 - 1. Waves and Particles 2. Interference of Waves...

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Unformatted text preview: 1. Waves and Particles 2. Interference of Waves 3. Wave Nature of Light 1. Double-Slit Experiment reading: Chapter 22 2. Single-Slit Diffraction reading: Chapter 22 3. Diffraction Grating reading: Chapter 22 Light as a Wave: Wave Optics Chapter 22 The Nature of Light Particle or Waves? WAVE? PARTICLES? Before the beginning of the nineteenth century, light was considered to be a stream of particles 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 But he was wrong. LIGHT IS A WAVE. The Nature of Light Particle or Waves? The Nature of Light Particle or Waves? How can we distinguish between particles and waves? For waves we have interference, for particles not! Christian Huygens argued that light might be some sort of a wave motion Thomas Young (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 The Nature of Light Wave Theory? During the nineteenth century, other developments led to the general acceptance of the wave theory of light Light as a Wave x y c- speed of light Plane wave x y changes only along one direction maximum minimum - wavelength Period of oscillation (time to travel distance of wavelength) T c = Frequency of light 1 c f T = = Light as a Wave Light is characterized by its speed and wavelength (or frequency ) c f Different frequency (wavelength) different color of light What is the speed of light? Measurements of the Speed of Light Fizeaus Method (1849) d is the distance between the wheel and the mirror t is the time for one round trip Then c = 2 d / t Fizeau found a value of c = 3.1 x 10 8 m/s c = 3.00 x 10 8 m/s- Speed in Vacuum! Speed of Light What is the speed of light in a medium? The speed of light in a medium is smaller than the speed in vacuum. To understand this you can think about it in a following way: The medium consists of atoms (or molecules), which can absorb light and then emit it, so the propagation of light through the medium can be considered as a process of absorption and subsequent emission (AFTER SOME TIME ) very schematic picture light (free propagation) atoms t Speed of Light- The speed of light in the medium The properties of the medium is characterized by one dimensionless constant n, (it is called index of refraction, we will see later why) which is equal to 1 for vacuum (and very close to 1 for air), greater then 1 for all other media c v n = Light in the Media E at a given point t T P 1 T t The same period (frequency) in all media, then air n c T n n = =- The speed of light in the medium c v n = Light as a Wave ( , ) sin 2 2 sin 2 x x E x t E ft E t = + = + x Distribution of some Field inside the wave of frequency...
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This note was uploaded on 02/15/2012 for the course PHYS 2212 taught by Professor Staff during the Spring '08 term at Georgia State University, Atlanta.

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lecture 2 - 1. Waves and Particles 2. Interference of Waves...

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