GATE 2016 ME (ME3) – Question 62
Two optically flat plates of glass are kept at a small angle θ as shown in the figure. Monochromatic light is incident vertically. If the wavelength of light used to get a fringe spacing of 1 mm is 450 nm, the wavelength of light (in nm) to get a fringe spacing of 1.5 mm is _________
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Correct answer: 674 to 676
Explanation
For a fixed small wedge angle in air, fringe spacing β=λ/(2θ). Consequentlyλ₂/λ₁=β₂/β₁=1.5/1. Multiplying450nm by1.5 gives **675nm**. The wedge geometry is unchanged between the two measurements.