Red Fringe Count in Young's Double Slit Experiment

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Homework Help Overview

The discussion revolves around a problem related to Young's double slit experiment, specifically focusing on the interference pattern produced by red light with a wavelength of 700nm, following an initial setup using blue light of 450nm. The original poster is attempting to determine how many red fringes will be visible on a screen placed 1.5m from the slits.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are questioning the validity of the calculations presented by the original poster, particularly the use of sin(90) in the context of maximum fringe order. There is also discussion about the implications of the screen size and its relation to the number of visible fringes.

Discussion Status

The discussion is ongoing, with participants exploring various interpretations of the problem and questioning the completeness of the original question. Some guidance has been offered regarding the potential need to clarify the dimensions of the screen to accurately determine the number of visible fringes.

Contextual Notes

There are indications that the original question may be incomplete or contain errors, particularly regarding the screen dimensions and the relevance of the blue light setup. Participants are encouraged to verify the details provided in the problem statement.

somecelxis
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Homework Statement



In a Young's double slit experiment , blue monochromatic light of wavelength 450nm is used to illuminate the slits which are 0.60mm apart. A screen is placed 1.5m form the slit is used to catch the interfrence pattern .
If red light is used (700nm) , how many red light will be seen? the ans is 7

Homework Equations





The Attempt at a Solution


dsinθ = m λ
0.6x10^-3 ( sin 90 ) = m (700x10^-9)
m = 857
no fringe can be seen = 857+ 857+1 ..
What's wrong with my working?
 
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where does sin(90) come from?
 
Sin90 beacuse I wamt to calculate themaximum order of fringes. Is my concept wrong?
 
no fringe can be seen = 857+ 857+1 ..
What's wrong with my working?
I would agree with you. Perhaps the question is meant to say something like "a 1 metre square screen is placed 1.5m from the slits".

Can you work backwards, and work out what screen dimension would show just 7 bands either side of the central maximum?
 
Do you meam the fringe is only formed on 1mm square of screen?
 
somecelxis said:
Do you meam the fringe is only formed on 1mm square of screen?
If you were wanting to see just the first order fringe, yes, that might be about right. But didn't you say the answer is n=7?

Could you check the question, and make sure you haven't got some detail wrong.
 
Last edited:
How is the part about blue light relevant? It seems that the question is incomplete or mixed-up somehow.
 
NascentOxygen said:
I would agree with you. Perhaps the question is meant to say something like "a 1 metre square screen is placed 1.5m from the slits".

Can you work backwards, and work out what screen dimension would show just 7 bands either side of the central maximum?

that's the whole question i have typed above...
 

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