13.4 Double slit interference

From one source and two gaps 1 st bright fringe 1 st bright fringe central fringe

From one source and two gaps 1 st bright fringe 1 st bright fringe central fringe - the closer the slits become the wider the fringe separation. - waves of short wavelength give narrow fringe separation because blue light diffracts less.

Path difference Phase difference

Path difference Phase difference

W First bright fringe Central fringe screen Double Slit interference - theory

W First bright fringe Central fringe screen Double Slit interference - theory Ə D = wavelength = 600nm D = slit to screen distance = 2m S = slit separation = 0.5 mm W = fringe width = 1mm

For constructive interference at the screen: ( ie a bright fringe ) Wave fronts from S1 and S2 must arrive at the screen in phase with a path difference of a whole number of wavelengths

For constructive interference at the screen: ( ie a bright fringe ) Wave fronts from S1 and S2 must arrive at the screen in phase with a path difference of a whole number of wavelengths For destructive interference at the screen: ( ie a dark fringe ) Wave fronts from S1 and S2 must arrive out of phase with a path difference of half a wavelength

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