Diffraction Grating Teacher Lesson Plan:

Complimentary Teacher Lesson Plan

Diffraction Grating – The Study of Color & Light

Objective:            To gain an understanding of where colors originate (in light); how the colors of the rainbow combine to create the various colors (including white light); how color filters affect various colors.

Materials:             1) overhead projector and three (to adequately cover) half-sheets of black construction paper (4-1/4" by 11")

and a clear plastic photo display holder with foot to hang

over the top edge of the projection lens of the overhead projector

3) diffraction grating glasses (Rainbow Symphony)

4) colored gels or filter materials (available from science

supply houses such as)

5) clear light bulb (40 watt (cooler) preferably, but not

absolutely necessary); green, blue and red 25 party

light bulbs; inexpensive bug light; a small 3.5 watt

(or nearly so) fluorescent night light, easily obtained

at super drug stores or hardware stores

from the screen as is normal for projecting images; the spectra (rainbows)

are on either side of the projection window...

Project the white light on the screen and discuss the

makeup of the light...   Use the diffraction

grating (4" by 4") mounted (in plastic photo frame with

foot to hang on projection lens, if you have it) to hold it

flat over the lens, and note the wash of light into a

suggestion of colors (on the sides of the projection window

primarily); ask where this suggestion of color is

coming from...   Then while the students are watching,

place the three half-sheets of black construction paper

over the projection table so as to allow only light from a

strip about 1 cm wide to pass through; note the exquisite

definition of the colors of the rainbow on either

side of the narrow slot of dimmer white light...

A discussion of Newton’s discovery of passing a sample of

light through such a mechanism could be appropriate for higher

grade levels...   Again discuss where the light is coming from...

A discussion of diffraction versus refraction might be appropriate

Discussion: the various colors of the spectra are the slot of light

reproduced in the different energies (colors) and overlapping as

they blend from one to the next; each energy (color) bends

through the diffraction grating at different angles

(Note: the amount of bending from the central slot of light

is reverse order (red to violet) with a prism; an interesting

difference between diffraction and refraction)

1b) Use colored gels laid across the narrow slot to see the

effect of the various color filters on the light coming

through the slot (called a slit in a professional spectrograph)

and discuss what is happening to change the projected colors...

2) Use the diffraction grating glasses, one to a student,

to do the following; stress that the glasses represent a

light analysis tool and that scientists use basically the

same kind of tool, only much more sophisticated...

1) look at light from ceiling fixtures (they will anyway)

and light coming in through the windows; note that the light has the

same washed out appearance as the diffraction grating over the

projection lens of an overhead projector...

2) in a room darkened substantially, view the light of

a clear light bulb, with and without the light analyzers;

make a log of this on a log sheet

3) look at the light of a small fluorescent night light in

the same way as in 2; note that the shape of the

Discussion: (cont.)

night light is nearly an elongated slot

4) look at the light of the colored light bulbs as in 2

5) look at the light of the inexpensive bug light as in

2; note that the spectra is easily seen to be different;

(note that what scientists do is to see these differences

in great detail and to understand what causes the differences, such as

composition and temperature of source and filter

Resources:

Rainbow Symphony Inc.

6860 Canby Ave.  #120

Reseda, CA  91335

Tel: (818) 708-8400

Fax: (818) 708-8470

Toll Free: (800) 821-5122

ACTIVITY WORKBOOK

Color Analyzers

GEMS/Lawrence Hall of Science

University of California

Berkeley, CA  94720

(510) 642-7771

About 300 years ago, Sir Issac Newton saw a beam of sunlight through a glass prism. He discovered that light is made up of a spectrum of seven distinct visible colors. This spectrum of colors always appears in the same order. You can see this color spectrum (Red, Orange, Yellow, Green, Blue, Indigo, Violet and all the colors in between) when you look through your Rainbow Symphony Diffraction Grating Glasses. There are two color ranges that are not visible to our eyes in this spectrum: below red is infra-red and above violet is ultra-violet. In a rainbow after a rainstorm this same color spectrum appears in the same order. Rainbows are created when sunlight passes through rain drops that act as millions of tiny prisms.

The color of a solid object depends on the colors of light that it reflects. A red object looks red because it reflects red light and absorbs all other colors. A blue object looks blue because it reflects blue light and absorbs all other colors. A white object reflects all colors of light equally and appears white. A black object absorbs all colors and reflects no visible light and appears black. Just like when you color with too many colors in one area with crayons or markers, all colors are absorbed, none are reflected and it appears black!

NEVER look directly at the sun because it could damage your eyes.