A transparent plate of thickness 6 μm and refractive index 1.5 is gradually introduced in front of one slit of a Young's double-slit experiment using light of wavelength 600 nm. How many bright fringes cross the original central point during the complete insertion?
Physics · Wave Optics · young's dubble slit experiments
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Question

A transparent plate of thickness 6 μm and refractive index 1.5 is gradually introduced in front of one slit of a Young's double-slit experiment using light of wavelength 600 nm. How many bright fringes cross the original central point during the complete insertion?

Physics · Wave Optics · young's dubble slit experiments

G1 Physics · Accepted Answer

Extra optical path: Δ = (μ−1)t = 0.5×6 μm = 3 μm. One complete fringe shift corresponds to one wavelength. Since λ = 600 nm = 0.6 μm, number of fringe crossings = 3 ÷ 0.6 = 5. Hence the answer is 5.