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Transcript
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 Copyright 2009 CPO Science Can be duplicated for classroom use 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? __________________________________________________________________________________ __________________________________________________________________________________ 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? __________________________________________________________________________________ __________________________________________________________________________________ c. How do the colors in the white LED compare to the red, green, and blue LEDs combined? __________________________________________________________________________________ __________________________________________________________________________________ d. If you wanted to get yellow light, what part of the spectrum would the color filter have to absorb? __________________________________________________________________________________ __________________________________________________________________________________ 2 Copyright 2009 CPO Science Can be duplicated for classroom use 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? _____________________________________________________________________________________ _____________________________________________________________________________________ 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 Copyright 2009 CPO Science Can be duplicated for classroom use 3 Describe what happens when you look through two polarizers and rotate one of them. _____________________________________________________________________________________ _____________________________________________________________________________________ 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. _____________________________________________________________________________________ _____________________________________________________________________________________ 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. _____________________________________________________________________________________ _____________________________________________________________________________________ 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. _____________________________________________________________________________________ _____________________________________________________________________________________ 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? _____________________________________________________________________________________ _____________________________________________________________________________________ 4 Copyright 2009 CPO Science Can be duplicated for classroom use Light and Optics