Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Color Investigations
Essential Background
The Electromagnetic (EM) and Human Visible Spectra
Source: http://www.antonineeducation.co.uk/physics_gcse/Unit_1/Topic_5/topic_5_what_are_the_uses_and_ha.htm
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The human visible spectrum is one portion of the greater electromagnetic (EM)
spectrum
An easy mnemonic to use in remembering the colors that comprise the visible spectrum
(in order, from long to short wavelength) is “ROYGBIV” where “I” is indigo. White light,
what is normally seen in overhead lighting, is composed of all the colors of the visible
spectrum.
The Additive (RGB) Color Wheel
Source: http://www.d.umn.edu/~mharvey/th1501color.html
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Do you see what I see?
Lesson 3: Is seeing believing?
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June 2012
Humans possess “green,” “red” and “blue” cone cells
Green, blue and red can be considered “primary physiological colors”
Yellow, cyan and magenta can be thought of as “secondary physiological colors”; each
results from the simultaneous and equal activation of two kinds of cone cells
The perception of white results from simultaneous and equal activation of all three
kinds of cone cells
“Complementary physiological color pairs” are blue & yellow, red & cyan, and green &
magenta. An object of color X maximally absorbs light at the wavelength of its
complementary color
Non-primary and non-secondary colors (e.g., orange, grey and brown) result from
simultaneous and unequal activation of multiple cone cell varieties
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Monochromatic/White Light Emission
Instructions: Use as many of the below graphs as needed to sketch the spectra generated by
each light bulb in the experiments you do as a class. Label each graph.
Light Bulb Used:
Notes:
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Lesson 3: Is seeing believing?
June 2012
Light Bulb Used:
Notes:
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Light Bulb Used:
Notes:
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Monochromatic/White Light Emission: Questions
1. What happens to the graph when the probe is moved closer/further to/from the light
source?
2. Why were the room lights dimmed before the spectrophotometer was used?
3. If the white light bulb used isn’t truly full-spectrum, why do you suppose we perceive
the light it emits as white?
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Emissions from Multiple Lights
Instructions: Use as many of the below graphs as needed to sketch the spectra generated by
combinations of light bulbs in the experiments you do as a class. Label each graph. Your
sketches need not be precise. Based on your class discussion, answer the questions below.
Light Bulbs Used:
Notes:
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Light Bulbs Used:
Notes:
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Light Bulbs Used:
Notes:
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Emissions from Multiple Lights: Questions
1. Do you and the spectrophotometer always “see” the same thing? What does this
suggest about visual perception vs. optics? Use specific examples form the spectra
generated in this part of the lesson.
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Reflection
Instructions: Use as many of the below graphs as needed to sketch the spectra generated by
light reflected off of objects in the experiments you do as a class. Label each graph. Based on
your class discussion, answer the questions below.
Light Bulb Used:
Object Used:
Notes:
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Light Bulb Used:
Object Used:
Notes:
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Light Bulb Used:
Object Used:
Notes:
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Reflection: Questions
1. Do the reflected spectra change based on how you position the probe relative to both
the light source and the object?
2. How would you confirm that the spectrophotometer is measuring the light reflected
from the object, and not merely recording the emission spectrum from the light source?
3. Is the reflected spectrum generated by shining a given color of light on, for example, a
yellow M&M the same as the spectrum generated from reflecting that same color of
light off of a yellow Christmas tree ornament? What difference does the nature of the
material make?
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Absorption/Transmission
Instructions: Use as many of the below graphs as needed to sketch both the absorbance and
transmittance spectra generated by each liquid. Label each graph. Based on your class
discussion, answer the questions below.
Type of Spectrum:
Color of Liquid:
Notes:
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Lesson 3: Is seeing believing?
June 2012
Type of Spectrum:
Color of Liquid:
Notes:
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Type of Spectrum:
Color of Liquid:
Notes:
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Do you see what I see?
Lesson 3: Is seeing believing?
June 2012
Absorption/Transmission: Questions
1. Does a secondary color like yellow only transmit yellow light? Why might it transmit
light in other regions of the spectrum and still appear yellow?
2. How do the absorbance and transmittance spectra for each color compare to each
other?
a. Red
b. Blue
c. Green
d. Yellow
3. How do you imagine the darkness of the color would affect transmittance and
absorbance?
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