Date: Sat, 25 Sep 2004 20:38:33 -0400

Author: "Dick Heckathorn"

Subject: RE: Dispersion/diffraction demo using a slide projector/overhead projector


Another use of the overhead, holographic grating an cardboard with a
slit on the stage is to mount color filters over 1/2 x 3/4 inch openings
cut in a 2 x 4 inch card stock. I use 4 x 6 inch index cards. Directions
for making the cards that I use can be found at:

The top opening is always left open to show the complete projection of
the projector light.

Then up to 3 openings below the original opening can be covered with
color filters.

The result: The spectrum of the color filter(s) is seen directly under
the complete spectrum.

Enjoy, Dick

Helping teachers who facilitate, motivating students who learn.
Dick Heckathorn 14665 Pawnee Trail Middleburg Hts, OH 44130
Physics Teacher CVCA 4687 Wyoga Rd Cuyahoga Falls, OH 44224
330-929-0575 VM 120

-----Original Message-----
[] On Behalf Of Curry, Robert T
Sent: Friday, September 24, 2004 4:28 PM
Subject: RE: Dispersion/diffraction demo using a slide
projector/overhead projector

There is a neat variation on this that you can do. Put the grating in
front of the projector head as mentioned. On the stage of the OHP, make
a slit on half of it and a slat on the other half. In other words, as
you stand behind the OHP facing the screen,
the near half of the stage has two pieces of opaque paper or metal with
a narrow slit between them. The far half of the stage has an equally
narrow obstruction ("slat") in line with the slit. On either side of
the slat is unobstructed light from the stage.

What you see on the screen is a normal spectrum on top and a
complementary spectrum below it. Below red you see cyan, below green
you see magenta, below blue you see yellow. A great way to lead into
demos on additive and subtractive color mixing.

Bob Curry

From Sun Sep 26 06:02:13 2004