Two Light Waves Through Plastic

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Homework Help Overview

The problem involves two light waves traveling through different layers of plastic after initially being in phase in air. The key parameters include the wavelength of the light and the thickness and refractive indices of the plastic layers. The questions focus on determining the phase difference after the waves emerge and the type of interference that occurs when they are combined.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculation of phase shifts based on the properties of the materials and the geometry of the problem. There is an attempt to relate the phase difference to the number of cycles and to explore the implications for interference.

Discussion Status

Some participants are actively trying to calculate the phase difference and are sharing their findings, while others express confusion and seek further assistance. There is a mix of approaches being discussed, with no clear consensus on the correct method or outcome yet.

Contextual Notes

Participants are working under the constraints of the problem's parameters, including specific values for wavelength, thickness, and refractive indices. There is an indication of uncertainty regarding the calculations and the implications for interference type.

Dante Tufano
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So I'm on my last try for this question, and I could really use some help, I'm completely clueless..

Two waves of light in air, of wavelength λ = 460.0 nm, are initially in phase. They then travel through plastic layers as shown in Figure 35-36, with L1 = 4.00 µm, L2 = 3.50 µm, n1 = 1.20, and n2 = 1.60.

hrw7_35-36.gif


(a) What is their phase difference in cycles after they both have emerged from the layers and arrived at the same horizontal position?
_______________cycles
(b) If the waves at that later position are brought together to a single point, what type of interference occurs?

-closer to destructive interference
-cannot tell from the information given
-closer to constructive interference


2. I know that the change in phase is equal to (L/wavelength)(n-1)



3. I plugged in the given values, and got a phase shift of 4.565 radians for n2 and a shift of 1.739 radians for n1. These added to a shift of 6.304 radians. Since only the decimal matters, it's a shift of .304 radians. However, this is way off, since when I divide by 460nm to get the answer in terms of cycles, I get 661.63, which is wayyyy too large. Even then, I'm clueless on how to answer part b too. Can I please get some help?
 
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Anybody? I really need help with this one..
 
Anybody?
The slightest help would be amazing
 
Suppose, when the light enters the plastic sheet, the phase is zero.
The wavelength in the medium of n1 is 391.8 nm.
Number of waves in L1 is 4x10^-6m/391.8 nm. = 10.212
That means 10 full cycles plus 0.212 cycle. Hence phase difference is 0.212 cycle.
Now proceed.
 
Last edited:
Dante! Its a small world! This is Doug btw. I can't figure this one out for the life of me...
 

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