# Deducing the film thickness of this ques below:

• iCENA
In summary, when a thin soap film is viewed in sodium light using the normal reflection method, it will appear dark due to interference between light waves reflected from the front and back surfaces of the film. This occurs when there is a path difference of λ/2, or a phase difference of ∏, and no light is reflected. This effect is caused by the fact that light reflected from the air/film surface undergoes a phase change of ∏, while light reflected from the film/air surface does not. A very thin film, less than 1 wavelength, will also appear dark because there is no reflected light. The next thickness of film that will produce darkness is when the film is λ/2 thick, because the light travels

#### iCENA

a thin soap film is seen in sodium light by normal reflection method it appears totally dark deduce the possible values of film thickness given (myu)-refra.indx of liquid-1.333 and lambda wave.lgth-5893 angstrom

This effect is caused by INTERFERENCE between light waves reflected from the front face of the soap film and light waves reflected from the back face, after passing into the film.
The waves will 'cancel out' if there is a path difference of λ/2 (a phase difference of ∏)
and the film will look dark because there is no light reflected.
There is a strange fact about waves. Light reflected from the air/film surface undergoes a phase change of ∏, this is like being given a λ/2 kick out of step.
Light reflected from the film/air surface does not experience a phase change.
This means that a very thin film (less than 1 wavelength) will produce no reflected light.
This is why you can be aware of the dark film when the film is about to burst.
The next thickness of film that will produce darkness is when the film is λ/2 thick (this is the λ in the film material) because the light travels 1 wavelength through the film (there and back)
and the resulting total path difference is λ/2 because of the λ/2 at the front surface.

## 1. How is the film thickness of a film determined?

The film thickness of a film can be determined through various methods such as spectroscopic ellipsometry, interferometry, and profilometry. These methods involve measuring the change in light intensity or wavelength as it passes through the film, which can then be used to calculate the film thickness.

## 2. What factors can affect the accuracy of film thickness measurement?

Factors that can affect the accuracy of film thickness measurement include the type of measurement technique used, the refractive index of the film material, surface roughness, and the presence of multiple layers or interfaces within the film.

## 3. Is there a standard unit for measuring film thickness?

Yes, the standard unit for measuring film thickness is nanometers (nm). Other commonly used units include micrometers (μm) and angstroms (Å).

## 4. Can the film thickness be measured for any type of film?

Yes, the film thickness can be measured for any type of film, including thin films, thick films, and coatings. However, the measurement techniques and accuracy may vary depending on the properties of the film.

## 5. How does the film thickness affect the properties of a film?

The film thickness can significantly affect the properties of a film, such as its optical, electrical, and mechanical properties. Thinner films may have different properties than thicker films due to changes in surface-to-volume ratio and the presence of quantum effects.