Question

A glass plate (n = 1.60) is covered with a thin, uniform layer of oil (n = 1.29). A light beam of variable wavelength from air is incident normally on the oil surface. Observation of the reflected beam shows constructive interference at 511 nm. Determine the minimum non-zero thickness of the oil film.

Answer 1

The thickness of the oil film is 198 nm.

Step-by-step explanation:

Given that,

Refractive index of glass plate = 1.60

Refractive index of oil = 1.29

Wavelength = 511 nm

We need to calculate the thickness of the oil film

Using formula of path difference

`2nt=k\lambda`

`t=(k*\lambda)/(2n)`

Where, n = refractive index

t = thickness

`\lambda` = wavelength

Put the value into the formula

`t=(1*511*10^(-9))/(2*1.29)`

`t=198*10^(-9)\ m`

`t= 198\ nm`

Hence, The thickness of the oil film is 198 nm.