Download LAB, A2 Color, Polarized Light

SCIENCE
A2 Color,
B2 Polarized Light
Name: ____________________________
Period # ____ Date: ____/____/____
What happens when you mix different colors of light?
All the colors of visible light can be created artificially using a combination of three primary colors: red,
blue and green. In this investigation, you will use a white light source and color filters to discover what
happens when you mix different colors of light. You will also learn how the filters work.
Materials
•
• Light and Optics kit:
• LED lamps (flashlights)
• red, blue, and green lenses
• Laminated Graph Paper
• Screen (board)
• Flashlight Collars
• Diffraction Glasses
Mixing primary colors of light
1. Build a pyramid out of the red, blue,
and green LED lamps (see photo, right).
2. You should see three spots of color on
the screen (red-green-blue).
3. Move the lens and screen to make the
three spots overlap (like a Venn diagram)
and observe the colors on the screen.
• How many colors do you see in the light pattern on the screen?
• What color of light do you see when two LED light beams overlap?
Write your answers in Table 1:
Light and Optics
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1
How does a color filter work?
A red laser can produce a single pure color of red which can be useful in some applications. In the
light and optics kit, you have three LEDs with color filters; but just how ““pure”” are these color
filters? In this part of the investigation you will examine the light produced by each colored LED,
and learn how a color filter works. You will use the diffraction glasses to make your observations.
The diffraction glasses allow you to see the different colors of the spectrum that a light source
produces.
1. With the diffraction glasses examine the light from the flashlight with the red LED filter.
2. Using colored pencils, sketch what you see in the appropriate column of Table 2.
3. Repeat steps 1 and 2 for the green and blue LEDs.
4. Remove the color filter from one of the flashlights. Examine the light produced
by the white light and record your observations in the table.
R
O
Y
G
B
I
V
R
O
Y
G
B
I
V
R
O
Y
G
B
I
V
R
O
Y
G
B
I
V
Drawing conclusions :
a. Compare the colors in the red LED to those in the green LED.
What are the similarities and differences in the range of colors?
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b. Compare the colors in the green LED to those in the blue LED.
What are the similarities and differences in the range of colors?
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c. How do the colors in the white LED compare to the red, green, and blue LEDs combined?
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d. If you wanted to get yellow light, what part of the spectrum would the color filter have to
absorb?
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2
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Light and Optics
B2 Polarization
How does a polarizing filter work?
Polarization is a method of aligning the direction of light waves by blocking out some of the waves. We
know that light behaves as a transverse wave, which means that its movement is similar to a wave on a
rope stretched between two people. If you shake a rope up and down, a vertical wave travels down the
rope. A light wave traveling in a similar up-and-down pattern is said to be polarized in the vertical axis.
If you were to vibrate the rope side-to-side, you would create another wave. A similar light wave is said to
be polarized in the horizontal axis. Light waves from incandescent lights, fluorescent lights, candles, and
from the sun travel along many different axes, not just horizontal or vertical axes. Because the light from
these sources is made up of waves traveling on more than one axis, the light is said to be non-polarized.
The polarization of light
A polarizer is a partially transparent plastic that allows one polarization of light to pass through long, thin
molecules lined up in neat rows. Slits between the rows of molecules allow only light waves aligned with them
to pass through. As you rotate the polarizer, you allow different polarizations of light to pass through
Examining polarization
1. Take one polarizer. As you look through it, observe the effects.
Try rotating the polarizer and see if it makes a difference. Answer question 4(a).
What happens when you look through a single polarizer and rotate it?
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2. Take a second sheet of polarizer look through both sheets of polarizer together. Leave one fixed and rotate the
other one as shown in the diagram below. Observe how much light you see through both polarizers as you
rotate the second one.
_
Light and Optics
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3
Describe what happens when you look through two polarizers and rotate one of them.
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How do you explain what you see?
The light from the sun(or a lamp) does not have a single polarization. Because this light is a mixture of light
that is polarized in many different directions, we say this light is unpolarized.
Explain why the light is reduced passing through one polarizer.
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When the light passes through the first polarizer it becomes polarized.
Explain why rotating the second polarizer changes the amount of light you see coming through.
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Applications of polarization
The glare from low-angle sunlight reflecting off water and roads is polarized in the horizontal direction.
Ordinary sunlight is not polarized. Explain how polarizing sunglasses can stop most of this glare.
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Photographers often use polarizing filters on camera lenses. Imagine that a photographer is planning to take
pictures of a shallow river on a bright sunny day. How might pictures taken using a polarizing filter be different
from pictures taken without it?
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4
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Light and Optics