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What's the Frequency, Roy G. Biv?

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The electromagnetic spectrum

Objective

Students will discover and verify the relationship between Wavelength and Frequency of the Electromagnetic Spectrum.

Grade Level

6th through 9th grades

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Prerequisites

    Math

    Students should have had some Pre-Algebra, especially in the areas of manipulation of formulas and pattern recognition.

    Science

    Students should have had an introduction to the electromagnetic spectrum and the concepts of wavelength and frequency.

Warm - Up

Direct students to write for ten minutes in their journals summarizing the graphic on the electromagnetic spectrum shown above. Tell them to think about the relationships in and among the various wavelengths and the position of each type of radiation in the electromagnetic spectrum.

Materials

Teacher For each triad of students
roll of adding machine tape set of red, green and violet (purple) pencils
overhead to emphasize important points in introduction and warm-up manila folder
  meter stick or metric ruler
  pair of scissors
  4 books
  watch with second hand
  one strip of masking tape
  extra pencil
  data table

Introduction

The visible light from the Sun is actually composed of the colors red, orange, yellow, green, blue, indigo, and violet, which can become distinguishable when sunlight passes through a prism. A good way to remember the order of the colors is to note that the first letters of the colors spell out the name ROY G. BIV. We can think of light traveling in waves with properties of wavelength and frequency. Wavelength is the distance between identical locations on adjacent waves (see figure below).

Diagram of wavelength

Frequency is the number of complete waves, or wavelengths, that pass a given point each second. All light travels at the same speed, but each color has a different wavelength and frequency. It is their different wavelengths that cause the different colors of light to separate and become visible when passing through a prism.

Diagram of frequency

Look at the illustration of the visible spectrum above. Can you guess which color has the longest wavelength? It's red! The wavelengths of the other colors decrease in order, with violet light having the shortest.

In this hands on lab, you will construct a simplified model of different light waves in order to determine a constant relationship between wavelength and frequency.

Guided Practice or Developmental Procedure

(The teacher should pass the following out to each group in order for them to not only hear the procedure, but to see it as well. pdf version available)

NOTE: Reading pdf files requires the Adobe Acrobat Reader, which is available for free download from http://www.adobe.com/products/acrobat/readstep.html.

  1. Triad decides who is
    1. Recorder/ Reader
    2. Materials Manager/ Checker
    3. Time Keeper/ On Task Coordinator

  2. Materials Manager retrieves all materials listed from teacher.

  3. Recorder should draw a vertical line about 20 cm from the beginning of the adding machine tape and label it "Start" (see below). With the metric ruler, make a point 100 cm from the starting point. Draw a vertical line and label it "End". Cut the tape off of the roll leaving about 20 cm space between "End" and where you cut.

    Diagram of tape for Roy G. Biv lab

  4. Materials Manager should use the colored pencils to draw three evenly spaced horizontal lines along the tape from Start to End. Make the top line red, the middle line green and the bottom line violet to represent three different colors in the spectrum of light.

    (NOTE: The Time Keeper/ On Task Coordinator should continually keep everyone focused in order to complete this lab. He or she may also share in the completion of the tasks.)

  5. Recorder should divide the red line every 14 cm with dark marks in red pencil. The green line should be divided every 10 cm and the violet every 8 cm. The marks that you make on the three color lines will represent the different wavelengths of the different colors of light.

    (NOTE: The true wavelengths are actually measured in terms of angstroms. An angstrom is 10-8 cm or 0.00000001 cm. Red has a wavelength of 7800-6220 angstroms, green has a wavelength of 5770-4920 angstroms and violet has a wavelength of 4550-3900 angstroms. However, in this lab, the simple relationship among the visible light waves will be what is important.)

  6. Materials Manager should use masking tape to fasten the marked adding machine tape to a pencil.

  7. Recorder should cut a manila folder along its crease. Then cut a rectangle out of the center of one of the long sides. This rectangle should be about 10 cm high and 5 cm wide as shown below.

    Diagram of the manila cutout

  8. Materials Manager should set the manila folder cut out on the table supporting it with the four books (see below). Feed the end of the adding machine tape through the narrow space between the manila folder and the two back books until "Start" appears in the middle of the opening in the manila folder.

    Roy G. Biv lab setup

  9. Recorder should now be prepared with the Data Table and sit in front of the tape and manila folder model.

  10. Time Keeper should call "start" and begin timing as he or she slowly pulls the tape along. Try to pull the tape at about the same speed for every trial!

  11. Recorder should tally in the appropriate box on the data table every time he or she sees a wavelength mark. When "End" appears, tell the Time Keeper to stop timing.

  12. Each Triad should make a "trial run" and then repeat the procedure an additional 3 times.

  13. On the data table, Materials Manager determines and records the average number of wavelengths observed for each color and the average time (in seconds) from start to finish.

  14. Recorder should determine and record the frequency for each of your colored light waves. Note: frequency is defined as the number of wavelengths passing a given point per second.

Independent Practice

(The teacher should pass out the following worksheet to each student in order to assess individual understanding. pdf file available.)

What's the frequency Roy G. Biv?

Student worksheet

Name________________________________Date__________________Per./Mod______

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  1. Compare the wavelengths and frequencies of the three waves. Write about any patterns you notice in their relationship.

    __________________________________________________
    __________________________________________________
    __________________________________________________

  2. Which color has the shortest wavelength? ____________
    Which color has the longest wavelength? _____________

  3. Which color has the highest frequency? ____________
    Which color has the lowest frequency? _____________

  4. What is the relationship of the red wavelength to the green? __________________________________________
    Red to the violet?_________________________________

  5. What is the relationship of the red frequency to the green? __________________________________________
    Red to the violet?_________________________________

  6. From your answers to the questions above, name the relationship between wavelength and frequency in waves that travel at the same velocity like the waves measured in this lab.

    _________________________________________________
    _________________________________________________

  7. Remember that velocity = distance / time. What was the velocity of the waves in this lab? ____________________
    *NOTE: the actual velocity of light c = 2.99 x 108 meters per second, but for our purposes in this lab, it will appear only as fast as the Time Keeper is pulling the adding machine tape.
  8. Multiply the wavelength of the red wave by its frequency. Do this for the blue and green waves also and write the answers below.

    red ________________
    green ______________
    violet ______________

  9. What do you notice about the results? _________________________________________________
    _________________________________________________

  10. Write an new equation for the velocity of waves in terms of wavelength and frequency instead of distance and time.

    _________________________________________________

Assessment

Formative assessment and observation should be evident throughout the lesson. The worksheet, final questions during closure or a future quiz may serve as summative assessment.

Closure

Direct students to write for ten minutes in their journals summarizing the lab and all procedures in this lesson. Encourage students to then share their findings and what they might have written in their journals.

References

The general idea for this lesson plan was adapted from a lesson written by Dr. Charles W. McLaughlin which was found in Science Experiments on File.

The graphics and other information found within this lesson can also be found in Imagine the Universe! which is located on the World Wide Web. The URL for this site is http://imagine.gsfc.nasa.gov.

If words seem to be missing from the articles, please read this.

Imagine the Universe! is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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This page last updated: Wednesday, 06-Sep-2006 14:45:26 EDT