05prob - Physics 9B-C Assignment #5 Cole c 3 108 m = =10-12...

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Physics 9B-C Assignment #5 Cole [Q35.6] The wavelength for gamma rays is λ == × × c f 31 0 8 m 0 H z 20 =10 -12 m. (see p. 1157). Interference pattern will only be noticable if the distance between the sources í 100 ¬ - 1000 ¬ which means the distance between the sources would have to be about 1 - 10 Å or about the diameter of an atom! For example, see the calculation for y 3 = 1.4 ª 10 -8 m using d = 0.2 mm (p. 1157, example 37-11). The spacing between the interference maxima is too small to see. [Q35.14] The interference process must be coherent. The way thin films achieve cohenence is to reflect part of a wave train of the first surface and another part off the nearby second surface. Because both came from the same wave train, they will have a well-defined phase relation and will interfere coherently. But how long, L, is a typical wave train? If 2 t > L then the first wave will have left before the second one can meet up with it. An atom takes about 10 s to emit a wavetrain õ L = c( 10 s) = 3 ª 10 -4 m = 0.3 mm. If the film thickess is greater than about a tenth of a millimeter, the coherence is lost and the interference pattern washes out. [P35.10] φ π = 2 dy L = 20(2π) õ d L y × () × 20 20 502 10 1 2 9 m m 10.6 10 m -3 .
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This note was uploaded on 05/19/2008 for the course PHY 009B taught by Professor Cole during the Fall '07 term at UC Davis.

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05prob - Physics 9B-C Assignment #5 Cole c 3 108 m = =10-12...

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