Re: Young's Interference, on the cheap


hhc314@xxxxxxxxx wrote:
Sue, first of all coherent beams are not required for Young's
Experiment. When I performed this in college, we simply used a sodium
vapor lamp, which is not coherent.

<<coherent means that every ray of light is accurately
phase-synchronized
with each other. Monochromatic means that the light must be
composed rays of exactly the same frequency. Finally collimated
means that every ray would have exactly the same direction of travel.

"Coherent, Monochromatic and Collimated"
http://cactus.eas.asu.edu/partha/Columns/2002/05-06-laser.htm




Second, for Young's Experiment, you need to phase synchronous beams,
which is quite different from a coherent light source. You obtain this
by splitting the non-coherent light from a single beam to obtain two
beams.

Third, your comments make it obvious that you don't understand the
difference between interferrence and diffraction.

There is none.


Sue, I hope that you are majoring in a subject like art history or
finance, becasue if you were a student in one of my classes in physics
I would be duty obligated to flunk you.

No chance of that unless you can get a job at MIT.
http://farside.ph.utexas.edu/teaching.html
http://web.mit.edu/8.02t/www/802TEAL3D/visualizations/light/index.htm

Sue...

The double-slit experiment
http://physicsweb.org/articles/world/15/9/1/1

The Dual Nature of Light as Reflected in the Nobel Archive
http://nobelprize.org/physics/articles/ekspong/index.html


Harry C.



Sue... wrote:
hhc314@xxxxxxxxx wrote:

Front Office wrote:
I think I might have succeeded, on the cheap, in doing
Thomas Young's demonstration of the wave nature of
light. Photos are at:

http://www.flashevap.com/Young.jpg

I used a Radio Shack laser pointer and a piece of brass
shim stock with a pinhole in it and a 0.005-inch diameter
wire in front of the pinhole.

I projected the pinhole light about two meters across
my office and onto the wall, where I took photos of
what might be interference of the red light.

The version of the experiment I am copying is shown
at the site of the Cavendish Laboratory:

http://www.cavendishscience.org/phys/tyoung/tyoung.htm

[Top posting moved]

What did you use for the beam splitter? Young used two slits, and the
article that you cited employed a card. You did use something to split
the beam, right, since a pinhole will not do that.

The pinhole alone will give you a diffraction pattern, not an
interferrence pattern as in Young's Experiment. While both
interferrence and diffraction are both consequences of the wave nature
of light, they are quite different effects. Please take time to learn
the difference, else an error of this type can cost you dearly on an
advanced college placement exam.

For a simple sanity check, when you replicate the two beam experiment,
make some simple measurements and compute the observed wavelength. Then
compare your result with that published for your laser pointer.
Physicists and engineers refer to this as a sanity check, without which
you don't know what you are observing or its experimental validity.

Realize that I am trying to be helpful, not critical.

Good luck and kindest regards, Harry C.

The slot has two edges coherently illuminated.
The summation of two knife edge diffractors is
just as valid as the sum of two slot antenna.

I have to differ with your opinion that
~interference is not demonstrated because twin holes
are absent the device~

Twin edges probably makes a sharper pattern
than twin holes (2 edges vs. 4 edges)
'tho I haven't actually compared.

The dual slits of the Young's device are just to
comfort the grey matter between the ears that
wants think of particle light.

Note that the electon version lacks what we would
would normally consider 'slits' as well.
http://www.hqrd.hitachi.co.jp/em/doubleslit.cfm
The east and west edges of the biprism rod are
what does the heavy lifting.

Sue...






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Relevant Pages

  • Re: Youngs Interference, on the cheap
    ... the beam, right, since a pinhole will not do that. ... interferrence pattern as in Young's Experiment. ... Photos are at: ...
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  • Re: laser through pinhole
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  • Re: Youngs Interference, on the cheap
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    (sci.physics)
  • Re: laser through pinhole
    ... I got a pinhole of 5 microns and need at least 1 mW ... Use a convex lens to focus down the beam. ... the hole with a commercial laser pointer. ...
    (sci.optics)
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