Re: [Phys-l] A demo for biologists?

[ludwik kowalski <kowalskil@mail.montclair.edu>]

THINKING ABOUT THIS AGAIN:

Divergence of the beam 1 and of the beam 2 are essentially the same;  
when they arrive to the screen (at the output of the interferometer).  
For that reason, even a thick glass plate might not produce cyclic  
darkening. Rings of that nature would appear if one beam were parallel  
and another beam were not parallel.

Ludwik

On May 16, 2009, at 1:47 PM, ludwik kowalski wrote:

> On May 16, 2009, at 1:23 PM, Brian Whatcott wrote:
>
> > ludwik kowalski wrote:
> > > I was not thinking about "interference fringes;" I expect the
> > > glass area covered by a thin foil to be either much darker or much
> > > brighter that the area that is not covered. The contrast will depend
> > > on the film thickness. That would be an excellent demo for students.
> > >
> > > - - - - - - - - - - - - - -
> > > Ludwik Kowalski
> >
> > Perhaps you were overlooking that the fringe effect is caused by
> > cyclic
> > darkening of the field by phase differences in path length - the
> > sort of
> > effect that could be increased if part of the field is phase changed
> > in
> > one leg with a plastic film?
>
> Dear Brian,
>
> Yes, indeed; I was assuming that the beam consists of parallel rays.
> Cyclic darkening should be expected in a diverging or converging beam,
> even in a glass plate without a film. Will this prevent one from
> converting an invisible phase image into a visible amplitude image?
> This remains to be seen. A glass plate covered by a this film might
> not be the best possible approach. Suppose a glass plate is replaced
> by a thin film stretched over a hole, in a rigid frame. Suppose one
> half of the hole is also covered with the second thin film. In this
> case cyclic darkening will probably be absent. Do you agree?
>
> - - - - - - - - - - - - - -
> Ludwik Kowalski, a retired physics teacher and an amateur journalist.
> Updated links  to publications and reviews are at:
>
> http://csam.montclair.edu/~kowalski/cf/   http://csam.montclair.edu/~kowalski/my_opeds.html
>    http://csam.montclair.edu/~kowalski/revcom.html
>
> Also an ESSAY ON ECONOMICS at: http://csam.montclair.edu/~kowalski/economy/essay9.html
>
>
>
>
>
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- - - - - - - - - - - - - -
Ludwik Kowalski, a retired physics teacher and an amateur journalist.  
Updated links  to publications and reviews are at:

http://csam.montclair.edu/~kowalski/cf/   http://csam.montclair.edu/~kowalski/my_opeds.html 
   http://csam.montclair.edu/~kowalski/revcom.html

Also an ESSAY ON ECONOMICS at: http://csam.montclair.edu/~kowalski/economy/essay9.html