356CHAPTER 25 25.43A fringe shift occurs when the mirror moves distance 4λ. Thus, the distance moved (length of the bacterium) as 310 shifts occur is 9565010m3105.0410m50.4 m44shiftsLNµ−−×∆===×=25.44A fringe shift occurs when the mirror moves distance 4. Thus, the distance the mirror moves as 250 fringe shifts are counted is 95632.810m2503.9610m39.6 mshifts−−×==×=25.45When 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 tis vacNt=. The number of wavelengths that fit in this thickness while traveling through the transparent material is ( )nnt nnt===(). Thus, the change number of wavelengths that fit in the path down this arm of the interferometer is 1tnnvacNN N
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