What is the minimum thickness for destructive interference in thin film?

In summary, the problem is to calculate the minimum thickness of a film where the intensity of the reflected red ray is near zero. The given information includes the wavelength in the film as 4.81x10-7 m and the index of refraction as 1.38. The equation given is 2L=mλ for destructive interference, but the attempt at a solution using this equation yielded a wrong answer. Further clarification and explanation is needed to understand the problem and find the correct solution.
  • #1
TwoEyedHuman
4
0
1. Calculate the minimum thickness of the film for which the intensity of the reflected red ray is near zero.
(This is AP Physics B 2010 (c)ii.)
I found the wavelength in the film to be 4.81x10-7 m
nf=1.382. 2L=mλ (destructive interference)

The Attempt at a Solution


My first attempt yielded a result of L=2.41x10-7 m
That was using the equation given. I checked the result in the scoring guideline, and it was wrong. I read the explanation, but I was confused by it and didn't want to write down an answer I didn't understand.
 
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  • #2
Can you state the complete problem.
 
  • #6
TwoEyedHuman said:
2. 2L=mλ (destructive interference)
What phase difference is required for destructive interference? What value of 'm' must you use in this equation?
 
  • #7
Doc Al said:
What phase difference is required for destructive interference? What value of 'm' must you use in this equation?

That is where I get confused.
 
  • #8
TwoEyedHuman said:
That is where I get confused.
Well, for two rays to destructively interfere--cancel out--what must be their phase difference?
 

1. What is thin film interference?

Thin film interference is a phenomenon that occurs when light waves reflect off of two surfaces of a thin film, resulting in constructive and destructive interference. This creates a pattern of light and dark bands, known as interference fringes, which can be observed in various materials such as soap bubbles, oil slicks, and anti-reflective coatings on glasses.

2. How does thin film interference work?

Thin film interference is based on the principle of superposition, where two or more waves combine to form a resultant wave. In this case, the incident light wave reflects off of both the upper and lower surfaces of the thin film. When the reflected waves meet, they interfere with each other either constructively (peaks aligning with peaks) or destructively (peaks aligning with troughs), resulting in the interference pattern.

3. What factors affect thin film interference?

The two main factors that affect thin film interference are the thickness of the film and the wavelength of the incident light. The thickness of the film determines the path length difference between the two reflected waves, while the wavelength of the light determines the spacing of the interference fringes.

4. What are some real-world applications of thin film interference?

Thin film interference has many practical applications in industries such as optics, electronics, and coatings. It is used in the production of anti-reflective coatings on glasses, interference filters for cameras and telescopes, and in the manufacturing of LCD screens and solar cells.

5. How is thin film interference different from other types of interference?

Thin film interference is unique in that it is caused by the reflection of light waves off of two surfaces of a thin film, rather than the interaction of multiple light sources. This results in a distinct pattern of interference fringes that can be observed and studied, making it a useful tool in scientific research and technological advancements.

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