∆λ∆∆=−λλffcf2where f = c/λis used. The negative sign means that an increase in frequency corresponds to a decrease in wavelength. We may interpret ∆fas the range of frequencies that can be resolved and take it to be positive. Then, 2cfNm∆=and ∆fcNm=λ. (b) The difference in travel time for waves traveling along the two extreme rays is ∆t = ∆L/c, where ∆Lis the difference in path length. The waves originate at slits that are separated by (N– 1)d, where dis the slit separation and Nis the number of slits, so the path difference is ∆L= (N– 1)dsin θand the time difference is ∆tNdc=−1bgsin.If Nis large, this may be approximated by ∆t = (Nd/c) sin . The lens does not affect the
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