Understanding the Role of Convex Lenses in Fraunhofer Diffraction

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Homework Help Overview

The discussion revolves around the behavior of light as it passes through convex lenses in the context of Fraunhofer diffraction. The original poster expresses confusion regarding the expected convergence of light rays after passing through a convex lens, particularly in relation to the setup involving a monochromatic light source and a narrow slit.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster questions whether the second convex lens is diverging the rays instead of converging them, despite the expectation that it should converge them. Other participants provide differing observations about the behavior of the rays, with some affirming that the rays are indeed converging.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the lens behavior. Some guidance is offered regarding the nature of the rays, but there is no explicit consensus on the original poster's confusion about the teacher's demonstration.

Contextual Notes

Participants are grappling with the definitions and behaviors of convex lenses in the context of diffraction, and there seems to be a lack of clarity regarding the visual representation provided in the image referenced by the original poster.

Prashasti
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Homework Statement


A monochromatic source of light 'S' is placed at the principal focus of a convex lens 'L1'. A parallel beam of light or a plane wave front is incident on the narrow slit represented by AB (its width - 'a')

Homework Equations


So, what my teacher did was,
She showed diffraction of the light rays as they pass through the slit.
And then she made the rays to meet at a point 'P'.
Look at the image. Doesn't the convex lens L2 seem to be actually 'diverging' the rays? Shouldn't it 'converge' them?
I'm literally confused about it, because all the books seem to support my teacher.
singleslitexpt.png
 
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Prashasti said:
Doesn't the convex lens L2 seem to be actually 'diverging' the rays? Shouldn't it 'converge' them?
Looks like it's converging to me. In this image, the left lens is converging and the right lens is diverging.

foclen.gif

Image compliments of http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/foclen.html
 
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Yes the parallel rays are converging. They were parallel and are now drawing together.
 
Does it mean why my teacher did was wrong?
 
Jilang said:
Yes the parallel rays are converging. They were parallel and are now drawing together.
I 'm talking about the second lens...
 

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