light - Physics 54 Light Your food stamps will be stopped...

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Unformatted text preview: Physics 54 Light Your food stamps will be stopped effective March 1992 because we have received notice that you passed away. You may reapply if there is a change in your circumstances. Letter from S.C. Dept. of Social Services Overview Because of its special importance to us, we will give detailed treatment to the part of the spectrum of electromagnetic radiation with wavelengths in or close to the visible region. The human eye is sensitive to wavelengths from about 400 nm to about 700 nm. Radiation with somewhat shorter wavelengths constitutes the ultraviolet while that with somewhat longer wavelengths is the infrared. Most ordinary objects have dimensions large compared to these wavelengths. As a result, diffraction effects (to be discussed later in detail) are often negligible and we can treat the propagation of light energy as though it moves in straight lines, called rays. This treatment is called the ray approximation . The description of light propagation in rays is geometric optics . There are many phenomena which demonstrate conclusively that light does not always travel exactly in straight lines, but exhibits intensity distribution patterns typical of wave interference . The description of these phenomena is wave optics . Being an electromagnetic wave, light possesses E-Felds and B-Felds, perpendicular to the direction of energy propagation. Light phenomena which vary with the speciFc direction of (say) the E-Feld are called polarization effects. We will start with a discussion of the general properties of light, including the types of sources that emit it. Next we will discuss polarization phenomena. We will then use the ray approximation and discuss formation of optical images. inally we will discuss the wave nature and analyze the corresponding interference phenomena. Sources of light Earlier we briey discussed radiation by classical sources of e-m waves, such as oscillating electric dipoles. These operate on the basis of the classical principle that accelerated charges radiate energy as e-m waves. If the motion of the charge is periodic the frequency of the emitted waves will be the same as that of the charges oscillation. PHY 54 1 Light But the frequencies of visible light (around 10 14 Hz) are too high to be produced by macroscopic size oscillating dipoles. Visible light arises from processes involving microscopic objects such as atoms and molecules. The details remained mysterious until the 20th century. It required discovery and understanding of both the quantum nature of e-m radiation and the quantized nature of atomic and molecular energies. We now know that e-m radiation comes in small packets (originally called quanta but now called photons ), in each of which there is energy and momentum given by E = hf , p = h / = E / c ....
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This note was uploaded on 10/19/2011 for the course PHYSICS 54L taught by Professor Thomas during the Summer '09 term at Duke.

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light - Physics 54 Light Your food stamps will be stopped...

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