1. Light of wavelength 680 nm falls on two slits and produces an interference pattern in which the fourth-order fringe is 38 mm from the central fringe on a screen 2.0 m away. What is the separation of the two slits?
(A) 1.4×10−4m
(B) 2.1×10−4m
(C) 2.8×10−4m
(D) 4.2×10−4m
(E) 5.6×10−4m
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