[Phys-l] A demo for biologists?

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

On May 14, 2009, at 5:33 PM, John Clement wrote:

> > Rumor around here is that hypothesis testing as "the scientific  
> > method"
> > originated with the biologists, partly as a way to move them away  
> > from
> > being
> > nothing more than taxonomists.  In order for biology to gain the
> > scientific
> > stature of chemistry and physics they needed to do more experiments,
> > create
> > more theories, and do more experiments to substantiate the theories.
>
> This certainly jibes with what I have observed in the literature.
> Biologists do seem to embrace it more.

One thing that biology students would probably appreciate is a good  
demo of "phase imaging." Here is an idea that I have never tried.

Suppose a laser beam is expended (with two lenses) to a diameter of  
about 1 cm^2. Then it is split into two beams, like in an  
interferometer, and recombined into one beam projected into a screen.  
Suppose a small piece of glass (a microscopic slide) or plastic is  
partially covered with a transparent foil of thin plastic (mylar).  
Placing this transparent object into one of the beams would probably  
create a contrast (for example, mylar-coated area being darker or  
brighter that the other area. Stretching the film (reduction of  
thickness) would probably change the contrast.

Have someone tried such demonstration? Biologists often use phase  
microscopy without understanding it. Such demo, if it works, would  
probably by appreciated by many.  This idea, by the way, came to me in  
a dream, last night.


- - - - - - - - - - - - - -
Ludwik Kowalski, a retired physics teacher and an amateur journalist.  
Updated links  to publications and reviews are at:

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