Mystery Solved by R & D:
R = Research and Reflection & D= Development and Diffraction

Objectives:

• Students will build a simple spectrometer to analyze the diffracting patterns of different types of light sources. They will use diffracting lenses or other alternate tools to observe how the light waves are bent at the microscopic slits and spread into patterns of color, darkness and light.
  

• Using reflective properties, students will sample different materials under the same light intensity and source, to identify the reflective patterns of different materials.
  

• Given a mystery material, students will use the data previously collected to identify it. Given a mystery light source, students will match its spectrographic pattern to identify it from a previously analyzed sample. Students will begin to identify the electromagnetic spectrum as a tool used by scientists to identify patterns of color emitted from light sources or reflective surfaces.
  

• Students will use remote sensing images to study different sources of reflected light on Earth and the characteristics needed to identify them. Students are introduced to the concepts of infrared and ultraviolet wavelengths, as those frequencies extending beyond the visible spectrum. Also, they will be introduced to the tools needed to analyze these frequencies, as an extension of our eyes.
  

Time Duration: Two 50-minutes sessions

Grade Level: 6-8

Concepts Explored:
scientific processes, energy, patterns of change, systems and Interactions, communication, comparison, inference, classification, sequencing, organization, evaluation and synthesis

Vocabulary:
spectrometer, diffraction, diffracting lens, wavelength, reflection

Grouping: groups of 4

Materials Per Group:

• 4 paper towel rolls
  
• flashlight
  
• 4" x 1" squares of diffracting lens film
  
• piece of aluminum foil
  
• Images of remote sensing; day and night, countryside vs. city/urban setting
  
• 8 strips of colored and textured papers, fabrics, plastics and mylar.
  
• scissors
  
• recording paper/page
  
• 1 shoe box
  

Advanced Preparation:

• Gather shoe boxes, paper towel and TP rolls, or other enclosed containers, so they may be punctured and cut.

• Have available a variety of construction paper color strips, textured fabrics in solid colors and remnants of wall paper patterns. (Approx. 2"x3" samples)

• Cut ahead of time a class set of diffraction grating film into 1" squares.

• Gather leaves and pennies.

• Buy plastic report covers of different colors or use cutouts of plastic tubs, lids, lacquered wood and plastic bags.

Teacher Resources:
National Science and Technology Week Publication, National Science Foundation, Washington DC., 20550.

Supply Sources:
Wall paper stores may donate sample books of old patterns they no longer carry. Interior decoration stores may donate paint samples and wood pieces.

Technology:
3,2,1, Contact Video on Light
CD ROM Geo Media - USGS
"The Blue Planet" CD ROM, Now What Software, San Francisco

Teaching Tips:

• While building the mystery boxes for analysis of materials, facilitate and guide students to identify what is a variable and what are their controls. i.e. the size and shape of each item being studied needs to be the same. The intensity of light, the angle of the beam and the distance from the object also need to remain constant. The only variable is the type of material being seen. Other objects can be used to reach the same effect of diffraction:
  
  • Place two pencils taped together very close to the light source and observe the light traveling through the narrow space between them.
    
  • A piece of cloth, a feather, a human hair or any other object with thin spacing between parts can be used to create pathways of light to bend, thus diffracting.

Background:
A spectroscope is a tool used to separate light into its different colors (wavelength frequencies). In order to separate the light, either prisms or diffraction grating film are used. The diffraction grating is a piece of glass or plastic, which has even parallel lines on its surface. In between the lines are open spaces or slits, through which different wavelengths of light pass. As the light travels through the slits, it bends. The angle at which the light bends is proportional to the length of the light. For example, the red light has a longer wavelength than blue; therefore, it bends more than the blue light. The narrower the slit, the more the light spreads out. Spectrometers are used to find out the color emissions of stars and other celestial bodies, giving clues as to their composition.

Procedure:
Day 1:
Becoming familiar with the light spectrum and use of a spectroscope.

1. Use paper towel tubes, aluminum foil and diffracting lenses to build a spectroscope.
   
   • cut two squares of aluminum foil, large enough to cover each end of the towel roll.
     
   • on one piece of aluminum foil, cut a square in the center, so you may tape the 1" piece of diffracting grating lens (make sure not to tape over the grating through the viewing window opening)
     
   • tape the aluminum foil to the roll, so the diffraction grating window is centered
     (See Figure 1 below.)

     

   • place the other aluminum foil piece to the other end and cut a narrow slit on the center as shown in the figure. This piece needs to be free, so it can be aligned to match the direction of the microscopic slits on the diffracting grating lens.
     

2. Look at different sources of light through the slit side, aligning it to the grating at the other end of the tube, by carefully rotating the foil. Once they are aligned, compare the patterns of spectra emitted from the different sources of light.

3. Have students draw two or three different patterns they saw. Which had a larger green band? Blue band? etc. What would happen if the slit were wider? Try it.

4. Have students observe and record the characteristics of an object which reflects light, i.e. a white board, a piece of mylar, a shiny leaf, a coin, a lacquered wood piece, etc.
   
   • Shine a light on the objects and observe their reflective characteristics.
     
   • Then observe each one of them through the spectroscope, while the light shines on them. How are they different? How are they the same? What conclusions can they draw from their observations?
     

5. Show graphic of electromagnetic spectrum (Figure 2) , and identify the location where the students have been investigating the energy emissions of light. Guide them to see the differences in energy wavelengths through the ultraviolet, and infrared sections of the EMS. Give examples of items familiar to the students which use such energy levels, i.e. microwaves, radios, TV remote controls, etc.

Assessment:
What would you see if the objects were exposed to sun light? Explain.

Day 2:
Observing Mystery materials in a dark box. Reflective properties. For this exercise, the room needs to be darkened, once the students have selected the items to place in the boxes. (Timing needs to be monitored, to ensure all objects are viewed when room is dark).

1. Open a small pin hole on one end of a shoe box and a small flap window on the top.
   
2. Without showing the mystery object to the team, one of the students places, opposite the pin hole, a sample of any of the materials listed below. Is it important that the pieces remain constant in size? Why?
   
   • colored construction paper - wall paper solid color/ textured piece
     
   • penny
     
   • aluminum foil
     
   • fabric
     
   • mylar
     
   • shiny leaf
     
   • plastic
     

3. Give the mystery object in the box to the other team members. Have them view through the pin hole and try to identify the object.
   
   • Open the top slip and have them describe what they see now.
     
   • Shine a flashlight through the top opening with a paper acting as a filter. What do they see? Does it make a difference what color paper blocks the top? Why?
     
   • Remove all obstacles and shine light in the box. Record the final finding.

4. Students should take turns observing and recording different objects.

5. What must happen in order for them to see and identify the object? Can they discern the details? What properties of the objects were visible when the light was very dim? Which colors /textures were more visible than others? Why?

6. What conclusions can be drawn from the types of materials viewed in the boxand the way light reflects from them? How does this exercise relate to remote sensing images of our planet? How are they similar? Different?

Assessment:
Given remote sensing images of day and night images, forest vs. urban and infrared vs. regular images of the same area, identify objects by their characteristics and the differences between the images.

Extensions
To best show the properties of reflection, refraction and diffraction, numerous sources are available and numerous activities can be performed such as:

• Pencil in a glass jar (an example of refraction)
  
• Using mirrors taped together with objects inside their opening (reflection)
  
• Shining a flashlight through a comb like piece of paper from different angles, and measuring with a protractor the pathways of light diffracted through the slits (diffreaction)
  

Books for reference for these types of activities are:

• "The Science Snack Book" The Exploratorium, 3601 Lyon St., San Francisco, CA 94123-9835

• "Sight, Light and Color", An Illustrated Encyclopedia, Science Universe Series, Arco Publishing Inc. 215 Park Ave South, New York, NY. 10003

---

Return to Top Down Project Menu