Question

A glass plate (n = 1.64) is covered with a thin, uniform layer of oil (n = 1.27). A light beam of variable wavelength from air is incident normally on the oil surface. Observation of the reflected beam shows constructive interference at 501 nm. Determine the minimum non-zero thickness of the oil film.

Answer 1

152.7 nm

Step-by-step explanation:

Refractive index of glass plate = n = 1.64

Refractive index of oil = n' = 1.27

wavelength = λ = 501 nm = 501 e-9 m

2n t = m λ , since it undergoes constructive interference.

Thickness = t = 501 × 10⁻⁹ m / 2 (1.64)

= 152.7 nm