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

[Brian Whatcott <betwys1@sbcglobal.net>]

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?

Brian W