- #1
riseofphoenix
- 294
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:(:(
Given 2 indexes of refraction, how do I figure out thickness of oil
- Thread starter riseofphoenix
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- Figure Oil Refraction Thickness
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Homework Help Overview
The discussion revolves around determining the thickness of an oil film given its index of refraction and that of water, along with the wavelength of light. The original poster expresses confusion about the relevance of the wavelength and the concept of phase reversal in the context of interference patterns.
Discussion Character
- Exploratory, Conceptual clarification, Assumption checking
Approaches and Questions Raised
- The original poster attempts to apply the formula for thickness based on the indices of refraction and wavelength but questions the necessity of the wavelength provided. They also seek clarification on the term "first order" in relation to interference and express confusion about phase reversal and constructive interference.
Discussion Status
Participants are engaging with the original poster's calculations and questions. Some provide insights into the concepts of phase reversal and constructive interference, while others encourage the poster to clarify their calculations further. There is an ongoing exploration of the underlying principles without a clear consensus on the original poster's understanding.
Contextual Notes
The original poster appears to be working under constraints of homework guidelines, which may limit the depth of explanation they can receive. They are grappling with foundational concepts in optics related to interference and refraction.
:(:(
- #2
tiny-tim
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hi riseofphoenix! 
show us your full calculations, and then we'll see what went wrong, and we'll know how to help!
show us your full calculations, and then we'll see what went wrong, and we'll know how to help!
- #3
riseofphoenix
- 294
- 2
tiny-tim said:hi riseofphoenix!
show us your full calculations, and then we'll see what went wrong, and we'll know how to help!
Given:
noil = 1.16
nwater = 1.33
λviolet = 400 nm - Question 1: why did they give me this if i didn't have to use it?
m = 1 (first order) - Question 2: what do they mean by the term "first order"? I never understand :(
t = ?
Equation to use:
2noilt = mλ
t = mλ/2noil
t = (1)(400 nm) / 2(1.16)
t = 400/2.32
t = 172.4 nm
I did it based off of this:
I don't understand their explanation though :(:(:(
Particularly this part: "Since nair < nair < nwater, light reflected from both top and bottom surfaces of the oil film experiences phase reversal."
Question 3: What's phase reversal??
Question 4: And why is this considered "constructive interference"? :(
Last edited:
- #4
riseofphoenix
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:'( *sadface*
- #5
tiny-tim
Science Advisor
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hi riseofphoenix!
you have used it!
it's like a diffraction grating … there are different angles at which there's constructive interference, and this is the first one
(basically, the difference in phase needs to be a multiple of 360° for constructive interference)
phase reversal is where the reflected ray is 180° out of phase with the incident ray
whether it happens depends on whether the refractive indexes are increasing or decreasing (you need to look this up, and study it!)
if there is phase reversal, you have to add 180° to the phase difference before you decide whether it's a multiple of 360°
riseofphoenix said:
you have used it!
it's like a diffraction grating … there are different angles at which there's constructive interference, and this is the first one
(basically, the difference in phase needs to be a multiple of 360° for constructive interference)
phase reversal is where the reflected ray is 180° out of phase with the incident ray
whether it happens depends on whether the refractive indexes are increasing or decreasing (you need to look this up, and study it!)
if there is phase reversal, you have to add 180° to the phase difference before you decide whether it's a multiple of 360°
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