20_Chapter 25 HomeworkCH25 Optical Instruments

20_Chapter 25 HomeworkCH25 Optical Instruments - 356...

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356 CHAPTER 25 25.43 A fringe shift occurs when the mirror moves distance 4 λ . Thus, the distance moved (length of the bacterium) as 310 shifts occur is 9 5 650 10 m 310 5.04 10 m 50.4 m 44 shifts LN µ  × ∆= = = × =   25.44 A fringe shift occurs when the mirror moves distance 4 . Thus, the distance the mirror moves as 250 fringe shifts are counted is 9 5 632.8 10 m 250 3.96 10 m 39.6 m shifts × = = × = 25.45 When the optical path length that light must travel as it goes down one arm of a Michelson’s interferometer changes by one wavelength, four fringe shifts will occur (one shift for every quarter-wavelength change in path length). The number of wavelengths (in a vacuum) that fit in a distance equal to a thickness t is vac Nt = . The number of wavelengths that fit in this thickness while traveling through the transparent material is ( ) nn t nn t == = () . Thus, the change number of wavelengths that fit in the path down this arm of the interferometer is 1 t n nv a c NN N
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