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What's the Frequency, Roy G. Biv? |
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Objective
Students will discover and verify the relationship between Wavelength and
Frequency of the Electromagnetic Spectrum.
Grade Level
6th through 9th grades |
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 |
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meter stick or metric ruler |
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pair of scissors |
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4 books |
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watch with second hand |
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one strip of masking tape |
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extra pencil |
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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).
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.
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.
- Triad decides who is
- Recorder/ Reader
- Materials Manager/ Checker
- Time Keeper/ On Task Coordinator
- Materials Manager retrieves all materials listed from teacher.
- 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.
- 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.)
- 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.)
- Materials Manager should use masking tape to fasten the marked adding
machine tape to a pencil.
- 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.
- 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.
- Recorder should now be prepared with the Data Table and sit in front of
the tape and manila folder model.
- 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!
- 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.
- Each Triad should make a "trial run" and then repeat the
procedure an additional 3 times.
- 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.
- 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______
- Compare the wavelengths and frequencies of the three
waves. Write about any patterns you notice in their
relationship.
__________________________________________________
__________________________________________________
__________________________________________________
- Which color has the shortest wavelength? ____________
Which color has the longest wavelength? _____________
- Which color has the highest frequency? ____________
Which color has the lowest frequency? _____________
- What is the relationship of the red wavelength to the
green? __________________________________________
Red to the violet?_________________________________
- What is the relationship of the red frequency to the
green? __________________________________________
Red to the violet?_________________________________
- 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.
_________________________________________________
_________________________________________________
- 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.
- 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 ______________
- What do you notice about the results?
_________________________________________________
_________________________________________________
- 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.
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