Confused on Constructive/Destructive Interference

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SUMMARY

The discussion centers on calculating the thinnest film that produces constructive interference for light reflecting off a film with a refractive index of n=1.6 and a wavelength of 575 nm. The user is confused about which interference equation to apply, specifically between the equations for constructive and destructive interference. The correct approach involves using the equation for constructive interference with one phase change, represented as 2T = m * t/n, where T is the film thickness, t is the wavelength, and m is the order of interference. The user must determine the smallest integer value for m to minimize film thickness.

PREREQUISITES
  • Understanding of interference patterns in optics
  • Familiarity with refractive indices and their implications
  • Knowledge of the equations for constructive and destructive interference
  • Basic principles of light reflection and phase changes
NEXT STEPS
  • Study the principles of constructive and destructive interference in detail
  • Learn how to calculate film thickness using the equation 2T = m * t/n
  • Research the concepts of hard and soft reflection in optics
  • Explore practical applications of thin film interference in coatings and optics
USEFUL FOR

Students in physics or engineering, particularly those studying optics, as well as educators and anyone involved in practical applications of interference phenomena.

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Confused on Constructive/Destructive Interference!

Homework Statement


A film with n=1.6 is deposited on glass. What is the thinnest film that will produce constructive interference in the reflection of light with a wavelength of 575 nm?


Homework Equations





The Attempt at a Solution


I have 2 equations that I can choose from...

Constructive Interference for 0 to 2 refl. phase changes
Destructive Interference for 1 refl. phase changes
2T = m * t/n
t = wavelength

Destructive Interference for 0 to 2 refl. phase changes
Constructive Interference for 1 refl. phase changes
2T = (m + 1/2) * t/n
t = wavelength

How do I know which one to use?

I chose the 2nd one because I assumed there was only 1 phase change.

How do figure out what m =?
 
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You can't just assume there's only one phase change. You have to see if the reflected beams of light undergo a hard or soft reflection.

As for the value of m, you want it to be as small as possible so that the thickness is as small as possible.
 
whats hard and soft? those terms are not in my book.
 

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