Re: Light source

["Donald E. Simanek" <dsimanek@eagle.lhup.edu>]

On Wed, 26 Feb 1997, George Spagna wrote:

At 09:58 PM 2/25/97 -0500, Tish Richey wrote:
> I would like to present the "light" section in Physics.  Unfortunately, I
> do not think I have the proper equipment.  I was thinking of purchasing
> eight pen light lasers.  But, recently I found a box of lights (plug in,
> 40-60 watts).  Can is use these with some type of box for ray tracings?

Two problems:

The light from the lamp must be collimated so that that portion of it
which passes through *each* slit is in a reasonably collimated (parallel)
beam. You may, of course, want the beams from each of the slits to be
divergent or convergent for particular purposes. This requires a lens, or
lenses, preferably cylindrical. You may have some cylindrical ones in your
stockroom for the "sighting with pins" experiment in ray tracing.

Light intensity is a problem. Usually mercury arc lamps are used, and even
then a darkened room is necessary. The high intensity lamps from modern
slide projectors can be adapted.

If you go the latter route, consider using a curved reflector for
collimation.  These lamps often have an internal reflector within the
bulb. Aim the lamp backward toward the curved reflector which in turn
sends light to the slits. A suitable curved reflector can be made with
metallized foil on a sheet plastic backing, bending the thing till it has
the right focal length to do the job. Food products are often
packaged in such shiny foil, the reflecting surface being on the
inside. I have some nice stuff from potato chip bags, and the
wrappers from Entenmann's Cereal Bars. Still, you waste a lot of the light
output. This in itself is a nice hands-on optics project for one of your
better students. It's something like the rubber band racers in that it is
a project to apply one's knowledge of physics in order to engineer
something to get the best results from a minimum of resources,
prefereably resources you recycle or have lying around unused. To do it
with lasers is no challenge at all..

Or consider making a light box to efficiently use three or five lamps,
one for each slit, with a lens for each, ensuring that nearly all the
light from each lamp squirts through its slit. You'd have to converge,
then diverge the light.

	-- Donald

......................................................................
Dr. Donald E. Simanek                            Office: 717-893-2079
Prof. of Physics                    Internet: dsimanek@eagle.lhup.edu
Lock Haven University, Lock Haven, PA. 17745          CIS: 73147,2166 
Home page: http://www.lhup.edu/~dsimanek            FAX: 717-893-2047
......................................................................