Question

A thin film of oil of thickness t is floating on water. The oil has index of refraction no = 1.4. There is air above the oil. When viewed from the air in the direction normal to the surface, there is constructive interference of reflected red light with l = 675 nm. Find the minimum thickness t of the oil film that will give constructive interference of reflected light with l = 675 nm.

Answer 1

t = 120.5 nm

Step-by-step explanation:

given,

refractive index of the oil = 1.4

wavelength of the red light = 675 nm

minimum thickness of film = ?

formula used for the constructive interference

`2 n t = (m+(1)/(2))\lambda`

where n is the refractive index of oil

t is thickness of film

for minimum thickness

m = 0

`2 * 1.4 * t = (0+(1)/(2))* 675`

`t = (0.5* 675)/(2* 1.4)`

t = 120.5 nm

hence, the thickness of the oil is t = 120.5 nm