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

[Brian Whatcott <betwys1@sbcglobal.net>]

I think this is what Bernard intended to describe, but was fearful to 
appear to be talking down to you or perhaps he felt you were unworthy of 
his time and effort:

take two fresh microscope slides and set a  1 cm wide strip of saran 
wrap across one short end on one slide, then sandwich it with a second, 
in hopes of leaving a very thin wedge of air between two slides.  
Optionally tape together both short ends of the sandwich.

Illuminate the slides with an expanded laser beam, a filtered beam from 
a compact fluorescent light fitting or a plain fluorescent.
Look carefully through the slide sandwich and you will see faint stripes 
- if the preparation was particularly careful, you will see the stripes 
across the short dimension progressing towards the saran sliver.

Brian W


ludwik kowalski wrote:
> Dear Bernard,
>
> What is CFL? What is this "it" that you tried? Did you use an  
> interferometer? If not then why do you think that fringes have  
> anything to do with your saran wrap?
>
> Ludwik, who is often confused by telegraphic style, and by acronyms  
> with which he is not familiar.
>
>
> On May 17, 2009, at 12:31 AM, Bernard Cleyet wrote:
>
>   
> > Aaagh -- not a microscope,  microscope slides.   I just tried it w/
> > saran wrap.  (0.0003"** = ~ 7.6 microns)   This is ~ 13 wavelength.
> > So ~ 26*** fringes over very ~ 3"  (v.~ 7 cm);  easily counted w/ a
> > magnifying glass, or unaided if equi-spaced.  Won't be as the glass
> > isn't stiff.
> >
> > I didn't count them, as I was hand holding it and the beam was not
> > wide enuff.  I also saw them (multicolored) with a CFL.  Using a CFL
> > and a green filter would be good.  A kitchen physicist would use
> > green food coloring in a glass of water?
> >
> > ** Measured with a 0.0001" X 0.050"  Mitutoyo Dial Thickness Gauge.
> > ***Assuming no Sr. moment.
> >
> > bc