An Interactive Ray Diagram for Convex Lenses
Posted on: October 16, 2012. Comments ( 1 )

Author: Ujjwal Rane, BE (Mechanical), M.Tech. (IIT Madras), MS (Arizona State University), parent of Gundecha Education Academy, Kandivali (East), Mumbai.

Ray Diagrams seem like a nightmare! To start with, there are two types of lenses and three types of mirrors. And the location, size, nature and orientation of the image varies with the location of the object. The cases quickly skyrocket to about 15 – 20 different diagrams! Remembering them does not sound like fun. What more, it could be risky too, because the diagrams vary just a little from one another and the cases can easily get mixed. Fortunately, there are better ways to cope with this diversity and you can even have some fun doing it!

First, we can remember just a few rules – at the least you need JUST TWO! Why? Because light travels in a straight line and two straight lines can meet in a unique point. So just drawing the path of two rays, can nail down the image! What more light is reversible! So it backtracks its own path when reversed.

Secondly, if we can interact with a ray diagram hands on, it percolates down to an intuitive level and take root there for good!

Let’s do both of these for a convex lens:

    A. The rules (use any two. But if you use all three, you can really impress the teacher J)
    i. Ray parallel to the axis, passes through the focus
    ii. Ray through the optical center passes un-deflected
    iii. Ray through the focus becomes parallel
    Now, did you notice rules (i) and (iii) are actually reverse of each other? And that is just natural because light always retraces its path when reversed!
    B. Finally let’s interact or at least see how the image varies with the change in objects position. We will not be able to drag and shift the object. But I have done that for you in this video clip:

    Watch how the image change in nature (real/virtual), size (magnified/diminished), orientation (upright/inverted) and location (between which two points, same or opposite sides of the lens etc.)

Watch it in full screen, pause it with a spacebar and just drag the slider back if you need to go over any part again. Hope you will enjoy it and not know when the three rules take root in your mind!


I am Ujjwal Rane, BE (Mechanical), M.Tech. (IIT Madras), MS (Arizona State University), Proud parent of: Anubhav and Aakanksha Rane from Gundecha Education Academy, Kandivali (East), Mumbai.


Comments (1)

 

  1.  
    Vasudev says:

    Very nicely explained. Thanks. Please share more of such videos.


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