Interference By a thin film

If we are to observe interference in a thin film, why must the film not be very thick (with thickness only on the order of a few wavelength)?

Interference of light, Thin film interference and Introduction to YDSE

Thin Film Interference & Wedge Film Interference

What is the minimum thickness of thin film required for constructive interference in the reflected light through it ? (Given, the refractive index of the film =1.5, wavelength of the lilght incident on the film =600 nm.

What is the minimum thickness of a thin film (mu=1.2) that results in constructive interference in the reflected light? If the film is illuminated with light whose wavelength in free space is lambda=500nm ?

Calculate the minimum thickness of a soap bubble film (mu=1.33) that results in constructive interference in the reflected light if the film is illuminated with light whose wavelength in free space is lambda=600nm .

Consider a case of thin film interference as shown.Thickness of film is equal to wavelength of light in mu_(2)

If wavelength 4500 Å and 6000 Å are found to be missing in the reflected spectrum in thin air film interference, the thickness of the film for normal incidence is nearly

Statement I: Thin films such as soap bubble or a thin layer of oit on watar show beautiful colors when illuminated by white light. Statement II: It happens due to the interference of light reflected form the upper surface of thin film.