Barrier of Diffraction: Different Wavelengths, Same Color?

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Discussion Overview

The discussion centers around an experiment involving a Barrier of Diffraction using Sodium Steam as a light source. Participants explore the relationship between color and wavelength as observed in the fringes of confluence produced during the experiment. The scope includes experimental observations, theoretical interpretations, and challenges faced due to unclear instructions and resource limitations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes the experiment setup and expresses confusion about obtaining different wavelengths for the same color in consecutive fringes of confluence.
  • Another participant requests clarification on the experimental procedure, emphasizing the need for precise details.
  • There is a question about whether the light source is Sodium Vapour or Sodium Flame, indicating a potential distinction in the experimental setup.
  • Some participants suggest that the source should only emit one wavelength, questioning the validity of measuring different wavelengths from the same color.
  • One participant provides equations used in the experiment and shares specific measurements, seeking an explanation for the observed differences in wavelength.
  • Another participant notes that the wavelengths calculated are outside the visible range, implying a possible error in measurement or calculation.
  • There is a discussion about the nature of diffraction and interference as potential explanations for the observed phenomena.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the experimental results, particularly regarding the relationship between color and wavelength. There is no consensus on the reasons for the observed discrepancies in wavelength measurements, and some participants challenge the validity of the findings.

Contextual Notes

Participants mention limitations in the clarity of instructions and the availability of resources, which may affect the accuracy of the experiment and the understanding of the underlying physics.

  • #31
kuruman said:
I believe your value for a is incorrect.
570 grooves/mm = 570 grooves/mm × 1000 mm/m = 5.7×105 grooves/m. Therefore a = 1/(5.7×105) m/groove = 1.75×10-6 m/groove.
Multiply by 1010 Angstrom/m to get a ≈ 18000 Angstroms/groove. This will increase your wavelengths by a factor of 10.

a is from the previous exercise I mentioned, which we did at the Lab, and checked it. Basically we did the same thing as here, but with Sodium Vapor, known wavelength (λ = 5893 Angstrom), for just one fringe (m=+-1) and using the formula for φ (tanφ = ...) and either (5) or (6) found a. The Professor checked it and said it was correct, so I have to use it here.

I don't think it's out of the question that all these values are incorrect, but since he told us to treat the exercise a certain way, I'll leave the results as is and ask him later. Just an FYI, he's a Post-Grad/Junior Professor so he might be glossing over some stuff to get it done quickly.
kuruman said:
Also, can you show a sample calculation of how you got the values that you got? They disagree with mine.

On edit: I agree with the first two calculations even though it appears you have the wrong value for a. I disagree with the other two after "And again". You might wish to consider doing these on a spreadsheet with the same formula for all. Then either all of them will be correct or all wrong but easy to trouble shoot.

I just took the equation you came up with, and plugged in the angles, in the real values, not the absolute ones. For the 1st Order I put m = 1, and for the 2nd m = 2.

1st Order:
sin(70.9 - (-60,1)) + sin(-41,9 + (-60,1)) = 2*1*λ/(18300*10-10 Angstrom) <=> λ = -2044 Angstrom

2nd Order:
sin(85,2 - (-54,7)) + sin(-26,9 + (-54,7)) = 2*2*λ/(18300*10-10 Angstrom) <=> λ = -1579 Angstrom

Huh. Those are obviously different from before. I honestly don't know why. Maybe I added them in their absolute values before? Are these anywhere close to reality?
 
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  • #32
Why are you using negative values for φ? I didn't. Like I wrote earlier, having the picture, on which the derivation of equations 5 & 6 was based, would help tremendously with the correct substitution of variables.
 

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