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# malusLaw - I nverse Square Law and Pola rization of L ight...

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Inverse Square Law and Polarization of Light Lab Reading Assignment: Chapter 33.3-33.7. Introduction Electromagnetic waves consist of oscillating electric and magnetic fields with the following characteristics: o E and B are perpendicular to each other; o E and B are in phase; o E × B gives the direction of propagation of the wave; o | E | = c | B | , where c is the speed of light. o The rate of energy transport per unit area is given by the Poynting vector: . o The time-averaged value of the Poynting vector is known as the intensity I and is given by: , where E m is the amplitude of the electric field. The Inverse Square Law: electromagnetic radiation from a point source spreads out isotropically in all directions. The intensity of the radiation at any given distance, r , from a source of power output P s is given by: Polarization of electromagnetic waves: o The plane defined by the axis of propagation of an electromagnetic wave and the direction of the electric field is called the “plane of polarization” (see Fig. 1);

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o A “plane polarized” wave or, equivalently, a “linearly polarized” wave is one whose plane of polarization does not change with time. o The light emitted from most common sources is “unpolarized.” In this case, the plane of polarization changes randomly with time, Polarizers and analyzers : when unpolarized light is transmitted through certain materials (e.g. “polaroid sheets” -- invented by E. H. Land in 1938), the transmitted light has half the intensity of the incident light and is linearly polarized parallel to a special axis. If a second identical sheet, or “analyzer,” is
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malusLaw - I nverse Square Law and Pola rization of L ight...

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