One slit of a double-slit experiment is covered by glass of refractive index 1.4 and the other by glass of refractive index 1.7. The original central bright position becomes the fifth bright fringe. Both plates have equal thickness and λ=4800 Å. Find their thickness in μm.
Physics · Wave Optics
JEE Mains Advanced

Question

One slit of a double-slit experiment is covered by glass of refractive index 1.4 and the other by glass of refractive index 1.7. The original central bright position becomes the fifth bright fringe. Both plates have equal thickness and λ=4800 Å. Find their thickness in μm.

Physics · Wave Optics

G1 Physics · Accepted Answer

The differential optical path introduced is (μ₂−μ₁)t=(1.7−1.4)t=0.3t. For the fifth bright fringe, this equals 5λ. Hence t=5λ/0.3=5(4800 Å)/0.3=8×10⁻⁶ m=8 μm.