Finding Focus Length in Broken Double Convex Lens

Click For Summary
SUMMARY

The discussion centers on determining the focal length of a broken thin double convex lens. When the lens is split into two halves and reassembled, the focal length of the combined arrangement is f/2, contrary to the initial assumption of 2f. This conclusion is reached by understanding that the power of a lens is inversely related to its focal length, indicating that a more converging lens results in a shorter focal length. The participants confirm that the correct focal length for the arrangement is indeed f/2.

PREREQUISITES
  • Understanding of lens optics, specifically thin double convex lenses
  • Knowledge of focal length and its relationship to lens power
  • Familiarity with basic optical equations
  • Ability to interpret lens diagrams and ray diagrams
NEXT STEPS
  • Study the principles of lens power and its calculation
  • Learn about the effects of combining multiple lenses in optical systems
  • Explore the concept of focal length in different types of lenses
  • Investigate practical applications of lens combinations in optical devices
USEFUL FOR

Students studying optics, physics educators, and anyone interested in understanding the behavior of lenses in optical systems.

Prashasti
Messages
63
Reaction score
2

Homework Statement


A thin double convex lens of focal length f is broken down into two halves at the axis. The two haves are then combined, as shown in the figure. What will be the focal length for the arrangements?

http://www.meritnation.com/app/webroot/img/shared/content_ck_images/images/Untitled(375).png

Homework Equations

The Attempt at a Solution


For (i), I think that the answer is infinite because any incident ray will either go undeviated or will be laterally displaced - but the combination will not be able to converge it.
upload_2015-2-10_17-57-20.png

Is it right?

And, about the second arrangement - I think it must be 2f, but in my book, f/2 has been given as the answer!
upload_2015-2-10_18-2-55.png
 
Last edited by a moderator:
Physics news on Phys.org
Your answers look good to me. I think you even realize that f/2 is the correct answer, based upon your drawing...

The combined lens will be more focusing -- i.e. shorter focal length. 2f is a focal length 2X as long. Can that possibly be right, given your picture?
 
  • Like
Likes Prashasti
Ahh! I got it!
Power is inversely related to focal length. Now, because the combination is "more" converging (more power), its focal length will be less. :headbang:
I think it's correct now.
Thanks!
:oldsmile:
 

Similar threads

Calculating Chromatic Aberration
  • · Replies 2 ·
Replies
2
Views
2K
Understanding Two Convex Lenses: Ray Diagram and Focal Lengths
  • · Replies 3 ·
Replies
3
Views
2K
Image with an Plano-Convex lens
  • · Replies 7 ·
Replies
7
Views
3K
Convex Lens Problem: Find Focal Length
  • · Replies 1 ·
Replies
1
Views
1K
Find the Power of a Bi Convex Lens
  • · Replies 5 ·
Replies
5
Views
1K
Help please -- convex lens problem and focul length
  • · Replies 2 ·
Replies
2
Views
1K
Calculate the focal distance of the duplicate
  • · Replies 3 ·
Replies
3
Views
1K
How to Obtain a Magnification of -2 from a Convex Lens?
  • · Replies 3 ·
Replies
3
Views
3K
Calculate the focal length of the spectacle lens
  • · Replies 3 ·
Replies
3
Views
3K
[LENS] Given focal length and height, find object distance
  • · Replies 1 ·
Replies
1
Views
3K