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Re: [Phys-l] Feynman's messenger lectures now available



Yes, the books cover ray tracing. But often, students focus so much on what happens to the three or four rays that they have rules for that they think that those are the only rays there are! I like to have them draw those rays in one color, but then as an exercise, add in a bunch of other rays that you can draw after you know where the image is. This is a necessary trick if you are going to use ray tracing to locate the image formed by a "virtual object" in two lens systems.

Also, the cover-half-the-lens question is a good one to ask while you still have your optics stuff lying around the classroom. It makes me smile when a student shows the initiative to actually try it out for themselves.

________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Bernard Cleyet [bernardcleyet@redshift.com]
Sent: Tuesday, May 25, 2010 2:47 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Feynman's messenger lectures now available

I thought most (haven't met one that didn't) texts discuss ray tracing. Is it too much of a leap from the previous to have a good idea what happens? (The texts, I believe, also discuss the non-lin. eye's response.)


bc discovered his not so nonlinear


p.s. I covered the top half of a projection lens (Kodak diapositive projector) and the field did not darken uniformly, but one would expect uniformity only in the position where one places a stop. The final lens was set back in the barrel, also. I tried another lens w/ the last lens at the mouth of the barrel; rather good uniformity. Finally covering half the lens (two stops; 1/4 transmission) produced much darkening! One quarter was much less, but noticeable.


On 2010, May 19, , at 15:14, Anthony Lapinski wrote:

For example, I
asked a student in my physics colleague's class, "If you cover the top
half of a lens, how will the image change?" He struggled with this and
said that his teacher never discussed this in class. To me, it's a
fundamental idea of optics.*

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