A glass plate (n = 1.64) is covered with a thin, uniform layer of oil (n = 1.28). A light beam of variable wavelength from air is incident normally on the oil surface. Observation of the reflected beam shows constructive interference at 605 nm. Determine the minimum non-zero thickness of the oil film.

Question

Amber Wall

Physics

31 January, 05:19

A glass plate (n = 1.64) is covered with a thin, uniform layer of oil (n = 1.28). A light beam of variable wavelength from air is incident normally on the oil surface. Observation of the reflected beam shows constructive interference at 605 nm. Determine the minimum non-zero thickness of the oil film.

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Lucas Hess · Answer 1

This is case of interference in thin films

for constructive interference in thin film the condition is

2μ t = (2n+1) λ/2; μ is refractive index of oil, t is thickness of oil, λ is wave length of light.

2 x 1.28 x t = λ/2, if n = 0

2 x 1.28 x t = 605 / 2

t = 118.16 nm.

the minimum non-zero thickness of the oil film required = 118.16 nm.