Why Do Light Beams Need to Be Parallel in Young's Double Slit Experiment?

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Homework Help Overview

The discussion revolves around the necessity of using parallel beams of light in Young's Double Slit Experiment (YDSE) and the implications of this requirement on the interference pattern observed. Participants explore the relationship between coherence, phase difference, and the alignment of light beams in the context of the experiment.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants question the definition of "parallel" beams and their significance in the experiment. Some inquire about the alignment of the light source and the slits, while others discuss the implications of using non-parallel beams and the necessity of maintaining a phase relationship for interference to occur.

Discussion Status

The discussion is active, with multiple interpretations being explored regarding the setup of the experiment. Some participants suggest that plane waves simplify the mathematical description, while others propose alternative configurations that could still yield interference, indicating a productive exchange of ideas without a clear consensus.

Contextual Notes

Participants express confusion over the requirement for parallel beams and the potential consequences of deviating from this setup. There is an emphasis on the coherence of light and the phase relationship necessary for interference, which remains a point of contention in the discussion.

Crystal037
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Homework Statement
Why parallel beam of light is used for ydse?
Relevant Equations
I(resultant) = I1+I2+rt(I1*I2cosx)
Where x is the phase difference
I know that ydse is based on interference of light when it passes through an obstacle having almost same aperture as the wavelength of light. Also they should be coherent to have a constant phase difference at every point. But I don't get why the light beams should be parallel?
 
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Crystal037 said:
Homework Statement:: Why parallel beam of light is used for ydse?
Homework Equations:: I(resultant) = I1+I2+rt(I1*I2cosx)
Where x is the phase difference

I know that ydse is based on interference of light when it passes through an obstacle having almost same aperture as the wavelength of light. Also they should be coherent to have a constant phase difference at every point. But I don't get why the light beams should be parallel?

Do you mean why are the slits are aligned perpendicular to the wavefront? If not, then what do you suggest?
 
No I mean why we take parallel beam of light i.e. Why do take the light source at the focus of convex lens and then that light is passed through the slit. What if we don't use the parallel light beams.
 
Crystal037 said:
No I mean why we take parallel beam of light i.e. Why do take the light source at the focus of convex lens and then that light is passed through the slit. What if we don't use the parallel light beams.

What's a "parallel" beam of light? Parallel to what?

The beam has to be focused at the slits. If not, it misses the slits and you don't have an experiment.
 
Parallel to each other I am talking about parallel beams of light that pass through both the slit
 
Crystal037 said:
Parallel to each other I am talking about parallel beams of light that pass through both the slit
If you have two beams of light that are not parallel to each other, then where are they coming from and what are they aimed at?

If you are proposing an alternative set-up why don't you describe it?
 
Basically you want plane waves for a simple setup (what you call parallel beam) in order to have the simplest mathematical description.
1579710286667.png

but the interference will also occur for a screen at an angle, a spherical wavefront coming from the left, etc.
Best thing to do (if you have a chance ) is to do the experiment and play with the setup !
 
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Crystal037 said:
Parallel to each other I am talking about parallel beams of light that pass through both the slit
If you have non-parallel beams, you will need for the light to have a phase relationship. Two flashlights, each pointed at one of two slits will not have a phase relationship.

An arrangement with half-silvered mirrors and two different convergent paths could do the trick. (Aka holography).
 

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