In Lloyd's single mirror experiment A light wave emitted directly from sources s interferes with a wave reflected from a mirror M. The interference pattern is formed on the screen which is kept perpendicular to the mirror and at a distance. $D=1 m$ from the source as shown . If the sources is at a distance of 1 mm from the plane of the mirror what is the fringe width when monochromatic light of 600 nm is incident from the sources

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$(a)\;6 \times 10^{-7} \;m \\ (b)\;3 \times 10^{-7} \;m \\ (c)\;4 \times 10^{-6}\;m \\ (d)\;3 \times 10^{-6} $