Group Members:
Big Science Ideas/Concepts:
Light color is a function of photon energy.
When different colors of light are mixed, they give the appearance of yet
other colors of light. A colored object absorbs light that
is different from the color of the object and reflects light that is the
same as the object. Objects get their color from pigments that act
to absorb some colors of light and reflects others.
Possible student misconceptions:
? The rules for mixing color paints and crayons
are the same as the rules for mixing colored lights.
? The primary colors used by artists (red, yellow
and blue) are the same as the primary colors for all color mixing
? The primary colors for mixing colored lights
are red, blue and yellow.
Measurable objectives:
? To explain how color addition and subtraction
work.
Material required:
Intended audience grade level/age:
8th or 9th grade Physical Science
Description of Lesson:
(Including an elicitation of student prior knowledge,
a blank student worksheet, an annotated teacherís version and connecting
dialogue)
Prior topics to get to this point:
? Electromagnetic spectrum and wave theory of
light
? Diffraction grating
? ? and pigments - how they work
? Vocabulary: filter, transparent, opaque, light,
pigment, photon energy, primary color of light, primary colors of pigment
Questions to elicit prior knowledge:
? If the light that fills this room is composed
of many different colors, what happens to the light absorbed by an object,
to produce a color?
? What are the primary colors of pigment?
Possible activities to clarify misconceptions:
? Use 3 beakers with water and food coloring
(red, green and blue). Using flashlights students will use these
onto a screen to produce magenta, cyan, and yellow. Different filters
can also be used on the flashlights to produce mixtures on a screen.
Let students see what different colors with light shown through them produce.
? Why is mixing light different from mixing paints?
Perhaps you have seen that red, blue and green light shone against the
same spot on a white wall combine to reflect a bright white light.
On the other hand, what would you predict if you mix magenta, cyan and
yellow. (Answer: paint yields a mixture that appears muddy.)
? Why are the effects different. When spotlights
are shone against the white wall, nearly all the light is reflected to
our eye. When green, blue and red lights combine, we see white.
This is called additive color mixing because our eye adds these colors
together. Mixing paint is different. For example, red paint
absorbs all colors except red. Only the red light is reflected by
the paint and comes to our eyes. The green paint absorbs all light
except for green, which is reflected and comes to our eyes. Mixing
red and green results in a substance that absorbs red and green light in
addition to all other colors so you get a mess - sort of a grayish brown
that in ideal circumstances would be black. This is called color mixing
by subtraction, since each paint in the mixture subtracts colors that are
reflected so that little color reaches our eyes.
Demo:
To reinforce the notion of the primary colors
of light - use a magnifying glass (convex, converging lens) to look
at a TV screen (VCR with source provided)
A possible extension:
Extension:
? How our eyes see colors
? How images are produced using color
? Internet resources from which to extend ? ideas
A relevant internet (or other) resource(and a
brief description of how it could enhance the lesson):
End of lesson assessment:
Assessment:
Questions provided