# The thinnest film in which the reflected light will be a max

• Any Help
In summary, the thinnest film for maximum reflected light is λ/4. The problem statement does not specify a substrate, so a low index film on a high index substrate may be a possible solution as well. There may also be some confusion or error in the problem setter's reasoning.
Any Help

## Homework Statement

Monochromatic light, at normal incidence, strikes a thin film in air. If λ denotes the wavelength in the film, what is the thinnest film in which the reflected light will be a maximum?

• A

λ/4

• B
3λ/4

• C
λ

• D

much less than λ

• E

λ/2

## Homework Equations

n air ∠ n glass
so at the first reflection it will cuase a 180° ray out of phase while the second ray reflected from the inside it will stay inphase because n air ∠ n glass
so for constructive interference: 2L=odd number*λ/2

## The Attempt at a Solution

least odd number is one , so L=λ/4 ?? why it is incorrect

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Your answer of λ/4 is correct. The problem statement does not mention glass.

Any Help
Well all I can do is sympathize. 1/4 should have been correct. Perhaps they have in mind a low index film on a high index substrate? Or perhaps the problem setter forgot about the 180 phase shift front to back and just got it wrong.

Any Help
Any Help said:
the thinnest film in which the reflected light will be a maximum minimum ?
possibly intended

Cutter Ketch

## 1. What is the thinnest film in which the reflected light will be a max?

The thinnest film in which the reflected light will be a maximum is known as the Fabry-Perot film. It is an interference filter made of two parallel, semi-transparent mirrors with a gap in between.

## 2. How does the Fabry-Perot film work?

The Fabry-Perot film works by allowing light to enter the gap between the two mirrors. Some of the light is reflected by the first mirror, while the rest passes through and is reflected by the second mirror. The reflected light then interferes with the incoming light, creating a pattern of constructive and destructive interference, resulting in a maximum reflection at certain wavelengths.

## 3. What is the significance of the Fabry-Perot film in scientific research?

The Fabry-Perot film is significant in scientific research as it allows for precise control and measurement of the wavelength of light. It is also commonly used in optical devices such as lasers, spectrometers, and telescopes.

## 4. Can the thickness of the Fabry-Perot film be adjusted?

Yes, the thickness of the Fabry-Perot film can be adjusted by changing the distance between the two mirrors. This allows for the tuning of the reflected light to different wavelengths, making it a versatile tool in various scientific applications.

## 5. Are there any limitations to the Fabry-Perot film?

The Fabry-Perot film has a limited range of usable wavelengths due to its reliance on interference patterns. It also requires precise alignment of the mirrors and can be sensitive to environmental factors such as temperature and pressure. Additionally, the reflected light may not be a perfect maximum, as there can be some loss of light due to absorption or imperfections in the mirrors.

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