TITLE OF LESSON PLAN:
The Color Spectrum: How Does It Work?

LENGTH OF LESSON:
Two class periods

GRADE LEVEL:
9-12

SUBJECT AREA:
Physical Science

CREDIT:
Karen Kennedy, former high school science teacher and educational consultant.

OBJECTIVES:
Students will understand:

1. the difference in wavelength size in the electromagnetic spectrum

2. that visible light makes up a very small portion of the electromagnetic spectrum

3. that light travels in a straight line and refracts when it passes from one substance to another, which is the principle behind why a prism separates white light into individual colors

4. that colors seen by the eye are a result of light being reflected, not absorbed

MATERIALS:
For this lesson, each group will need the following:

Meter stick or metric ruler (marked in millimeters)

Scissors

Scotch tape

Several pieces of paper in the following colors: red, orange, yellow, green, blue, violet, white, and black (paper will be cut into 1-inch-wide strips)

Black marker

Prism

Flashlight (optional)

A copy of The Color Spectrum: How Does It Work? Data Sheet for each student

PROCEDURE:

1. In this activity, students will create a model of the infrared, visible, and ultraviolet portions of the electromagnetic spectrum. The model they create will be made to scale based on wavelength. In order to complete this lab, students should understand the metric system and be able to convert between different metric units. They should also understand the concepts of wavelength and frequency.

2. Hand out data sheets to each student and divide the class into small groups of two or four. Make sure each group has the materials necessary for the activity.

3. Explain to students that the wavelengths for the visible, infrared, and ultraviolet portions of the spectrum are represented in meters on their data sheets. Students will need to complete a metric conversion calculation to find the length of the waves in nanometers. Explain to students that one nanometer is 10-9 of a meter. To put this length in perspective, tell them that the diameter of a penny is 19 billion nanometers. The scale that will be used to build their model of the spectrum is 1 nanometer equals 1 millimeter. So if a wavelength is Xnanometers, the model for that wavelength should measure Xmillimeters. Students will need to show the work they've done on their calculations in the space provided on the data sheet.

4. Work together as a class on the metric conversion calculation for red light. It is good to begin with red light rather than infrared, which is listed first on the data sheet, because the length of the scale model for infrared light is significantly longer than the scale models of any of the visible light colors. It is nice to let students discover this for themselves.

5. Have students fill in the scale length in the millimeters column on their data sheet for red light. Remind students that this column should always be the same as the final answer for wavelength in nanometers.

6. Now explain to students that the colored strips of paper will be used to represent the different colors in the visible spectrum. Red paper will be used for the wavelength of red light, orange paper for orange light, and so on. White paper will represent infrared, and black paper will represent ultraviolet.

7. Have each group cut a strip of red paper that is the same length as the number they have written in the column for scale length in millimeters. (If standard 8.5 × 11-inch paper was used to make the strips, one strip by itself will not be long enough to make the model. Point out to the groups that they may need to tape more than one strip together to get a long enough length of paper.)

8. Once groups have a piece of red paper that is 750 millimeters (75 centimeters) long, have them mark the actualwavelength of red light, 7.5 × 10-7 meters, on the strip. At this point, walk around the room and check on each group's progress.

9. Each group should now complete a metric conversion calculation and cut strips for each of the electromagnetic waves represented on the data sheet. When the groups have finished, they should have eight strips of paper of different lengths and colors in their model.

10. Have groups align their strips horizontally, directly underneath each other, with the longest strip (which should be infrared) on top and the shortest strip (which should be ultraviolet) on the bottom. Tape all of the strips together to make one large sheet. Hang all groups' models of the spectrum around the classroom.

11. Once groups have completed their model spectrum, give each a prism. Tell students to shine white light through the prism in order to see the visible spectrum they have just modeled. This demonstration works best if a flashlight is shone on the prism in a darkened room. If this situation is not possible, sunlight in a regularly lit room will also work, but the colors will be less vivid.

12. Students are to record the colors they see, from top to bottom, in the space provided on their data sheet. Discuss how wavelength contributes to the amount of refraction, or the deflection of light waves as they pass from one substance to another. Red light has the longest wavelength in the visible spectrum and therefore reflects the least. It is found at the top of the visible spectrum. Violet light has the shortest wavelength in the visible spectrum and therefore reflects the most. It is seen at the bottom of the spectrum. Discuss how the colors we see are actually light that is reflected by objects. For example, a red apple absorbs all colors of light exceptred. It is the red light that is notabsorbed that bounces back to our eye and gives the apple its red color.

13. When students have completed the prism portion of the activity, have them work out the problem at the bottom of their data sheet. Students may work as a group, but each student should have a solution written on his or her data sheet.

14. When students have finished, collect the data sheets from each group. Data sheets will serve as part of the evaluation for this activity.

ADAPTATIONS:

Adaptation for younger students:
Younger students will still be able to build a model of the visible spectrum. They should, however, be provided with both the actual wavelength andthe length that their scale model should be. This way they do not have to do the metric conversion calculations but still are required to use measuring skills. Once they have finished building their model, they too can look at how a prism separates white light into the visible spectrum.

DISCUSSION QUESTIONS:

1. A black piece of cloth and a white piece of cloth are left on a sunny windowsill. After an hour has passed, which will be warmer to the touch? Support your choice by using your knowledge of electromagnetic radiation.

2. Waves transport energy. Discuss any evidence you can think of that would prove, on this basis, that light is a wave.

3. Why can't humans see very well in the dark? Discuss some anatomical adaptations nocturnal animals have that allow them to survive successfully at night.

4. Radio waves and ultraviolet rays are both part of the electromagnetic spectrum. Why are we concerned about the amount of exposure to UV rays we may receive but not that of radio waves?

5. When we hear the word radiation,we think of danger. Discuss whether this is a reasonable reaction. Is visible light a type of radiation? If so, can it be harmful? What types of radiation should we be concerned about?

6. What health risks do you think may be associated with the use of cellular phones?

EVALUATION:

Students will be evaluated on four pieces of this activity for a total of 50 points:
-  Check each group's model to be sure that the measurements are reasonable and that the electromagnetic waves are in the correct order. Assign two points for each correct wave in the student model, for a total of 16 points. 
-  Check each student's data sheet to see that they have completed all of the calculations. Assign two points for correct calculations, including the one sample calculation completed together as a class, for a total of 16 points. 
-  Be sure that students have recorded the colors of the spectrum from the prism correctly. Assign one point for each of the colors they have recorded and add two points if they are in the correct order. This section is worth 8 points. 
-  And finally, check that students have answered the problem at the bottom of the data sheet. Student response to this problem is important because it should show a mastery of the metric conversion calculations and an understanding of size. This section is worth 10 points.

EXTENSION:

Money Magically Appears!
In groups of two, have students place a coin at the bottom of an empty cup and place the cup on a counter or desktop. One student should stand so that he or she can see the coin in the bottom of the cup and then walk backwards until he or she can no longer see the coin (this should only be one or two steps), remaining standing in that spot. The other student in the group should then pour water into the cup that holds the coin. The coin should then “magically” reappear into view for the student who has walked a couple of steps backwards. This extension shows that light refracts when it passes from one substance to another. As the student steps away from the cup, he or she can no longer see the coin because the angle has changed. When water is added to the cup, the speed of light is changed in the new medium, and the new path that the light takes hits the coin in the bottom of the cup.

The Colors We See
Divide students into small groups of two to four and give each group a shoebox, scissors, tape, and a piece of colored cellophane. Each group should have a different color of cellophane. Have students cut a rectangle out of the middle of the shoebox top and tape a piece of cellophane over the rectangular hole. Next they should cut a hole in one side of the shoebox big enough to shine a flashlight through. Each group should then take two different objects and place them in the shoebox, replace the lid with the colored cellophane panel, and shine a flashlight through the hole in the side. What differences do they observe in how the objects in the box appear when viewed through the colored cellophane panel? Trade objects and boxes until each group has had a chance to make several different observations.
  
If time is short, students can do this activity without making the box. They can simply observe different objects through different colors of cellophane and take note of any differences in appearance.

SUGGESTED READINGS:

Beyond Your Senses: The New World of Sensors
Hal Hellman. Lodestar Books, 1997.
Smart sensors are devices that are being developed to more perfectlymimic our own natural senses of vision, touch, hearing, taste, andsmell, and in fact to detect sensory information that is beyond ourordinary capabilities. This book describes technological breakthroughsthat are enabling us to experience and utilize a world unseen and unheard.

Close Encounters: Exploring the Universe with the Hubble Space Telescope
Elaine Scott. Hyperion, 1998.
The Hubble Space Telescope has helped revolutionize astronomers'understanding of our universe. After a brief history of telescopes, thisbook uses incredible photographs taken by the Hubble to help explainsome of the new discoveries that have been made about our solar system,our galaxy, and our universe.

WEB LINKS:

Activity: X-ray Imaging
This animated simulation of x-ray imaging shows you how this imaging technique can let you see inside an object like a car engine or a human body. The Shockwave plug-in is required to view this website.
http://www.explorescience.com/activities/Activity_page.cfm?ActivityID=42

CAT Scans
See how CAT scans let us peer into the human body without shedding one drop of blood. Jump over to Visible Human Project, where they are actually slicing up a (very dead) person and photographing each thin slice.
http://www.colorado.edu/physics/2000/tomography/index.html

X-Rays
Explore the physics underlying X-rays, light, and other kinds of electromagnetic radiation used in probing the human body. Interactive animations help simplify the physics of events beyond our senses.
http://www.colorado.edu/physics/2000/xray/index.html

How Radar Works
Radar is part of the electromagnetic spectrum, a fundamental element of the universe we live in.
http://www.elmendorf.af.mil/Units/90FS/radar.htm

Welcome to Amateur Holography
Is it real or is it a hologram? The boundaries between reality and virtual reality are blurring and have us pondering the wisdom of that old adage that "seeing is believing." Plans for making holograms with hand held laser pointers are available at this website.
http://members.aol.com/gakall/holopg.html

VOCABULARY:

electromagnetic spectrum
The range of frequencies of electromagnetic radiation. In theory, the spectrum's range is infinite.
Context:
The electromagnetic spectrum includes radio waves, infrared radiation, visible light, ultraviolet radiation, x-rays, and gamma radiation.

radio wave
An electromagnetic wave within the range of radio frequencies.
Context:
Radio waves are used to transmit radio and television signals.

spectrum
The range of frequencies of a particular type of radiation.
Context:
When a white light is shined through a prism, it spreads out to make a range of different colors with different wavelengths called a spectrum.

visible light
The area of the electromagnetic spectrum that is visible to the human eye.
Context:
Visible light is the portion of the electromagnetic spectrum with wavelengths between 400 to 700 nanometers.

wavelength
The distance between successive peaks or troughs in a periodic signal that is propagated through space.
Context:
Wavelength is the distance between the crest of one wave and the crest of the next wave.

ACADEMIC STANDARDS:

Grade Level:
9-12
Subject Area:
Physical science

Standard:
Understands motion and the principles that explain it.

Benchmarks:
Knows that waves (e.g., sound, seismic, water, and light) have energy and can transfer energy when they interact with matter.

Grade Level:
9-12
Subject Area:
Physical science

Standard:
Understands motion and the principles that explain it.

Benchmarks:
Knows the range of the electromagnetic spectrum (e.g., radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, x-rays, gamma rays). Electromagnetic waves result when a charged object is accelerated or decelerated and the energy of electromagnetic waves is carried in packets whose magnitude is inversely proportional to the wavelength.

DiscoverySchool.com
http://www.discoveryschool.com

Copyright 2001 Discovery.com.
Teachers may reproduce copies of these materials for classroom use only.