Understanding the Role of Convex Lenses in Fraunhofer Diffraction

AI Thread Summary
The discussion centers on the behavior of light rays passing through convex lenses in the context of Fraunhofer diffraction. A monochromatic light source is placed at the principal focus of a convex lens, creating a parallel beam that encounters a narrow slit. Participants express confusion regarding the role of a second convex lens, with some perceiving it as diverging the rays instead of converging them. Clarifications indicate that the rays are indeed converging after passing through the lens, aligning with standard optical principles. The conversation highlights the importance of understanding lens behavior in diffraction experiments.
Prashasti
Messages
63
Reaction score
2

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
 
Physics news on Phys.org
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
 
  • Like
Likes Prashasti
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...
 

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

Fraunhofer Diffraction Pattern Ratio of Power Densities
Replies
34
Views
3K
How Does the Fraunhofer Condition Affect Diffraction Patterns?
Replies
11
Views
2K
[Optics] Find maximum order number, Fraunhofer diffraction
Replies
7
Views
2K
Understanding Two Convex Lenses: Ray Diagram and Focal Lengths
Replies
3
Views
2K
Treating Oblique Incidence as a Fraunhofer Diffraction Problem
Replies
1
Views
1K
Double slits and convex lens interference
Replies
8
Views
2K
A Fourier optics model of a 4f system
Replies
1
Views
3K
I Using Diffraction (i.e., Fresnel Zone Plate) to defocus/diverge light
Replies
2
Views
2K
5 Questions dealing with Optics, image included
Replies
1
Views
3K
Emergent light produced by two lenses
Replies
15
Views
2K

Hot Threads

Recent Insights

Back
Top