Practice portal › Wave Optics › Interference and Young's Double Slit Experiment

Two light waves having the same wavelength λ in vacuum are in phase initially. Then the first wave travels a path L₁ through a medium of refractive index n₁ while the second wave travels a path of length L₂ through a medium of refractive index n₂. After this the phase difference between the two waves is

Asked in JEE Main 3rd Sept 2nd Shift 2020 · Slabs, media and modified set-ups

• (1) (2π)/λ((L₂)/(n₁)-(L₁)/(n₂))
• (2) (2π)/λ((L₁)/(n₁)-(L₂)/(n₂))
• (3) (2π)/λ(n₁L₁-n₂L₂)
• (4) (2π)/λ(n₂L₁-n₁L₂)

Step-by-step solution

Why the other options are wrong

• (1) Divides by the refractive index and also pairs the wrong length with each index.
• (2) Divides the path by n instead of multiplying: the wavelength shrinks in a medium, so optical path is nL.
• (4) Pairs each length with the other medium's index.

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