Procedure: (Time Required: 50 + Minutes)

Inquiry Activity Exploring Light and Prisms

Purpose: The students will be able to …  Identify that white light is made up of a mixture of many different colors of light.  Explain that a prism can be used to separate white light into many different colors of light  Explain how a colored filter works. Standard Addressed: (Indiana State Standards)

6.3.21 Investigate, using a prism for example, that light is made up of a mixture of many different colors of light, even though the light is perceived as almost white.

Required Materials:  Silly Putty  Black Poster Board  Glass Equilateral Prisms  Bubble wands / Wire frame shapes  Colored Filters (Green, Blue, and  Distilled Water Red)  Joy (dish soap)  White Computer Paper  Glycerin  Light Sources (**clear light bulbs**)  Scotch Tape

Introduction: Science facts are often contrary to our perceived experience of the world. If you think back to your childhood coloring memories you might remember that the coloring paper remained white only if you didn’t color on it, and when you combined many colors you got a very dark almost black color. This childhood experience may give rise to the misconception that the absence of all colors is white and black is the combination of all colors, but in fact the opposite is true. White light is the presence of all colors and black is the absence of all colors. Through involvement with this activity students should come to the understanding that white light is made up of a mixture of many different colors, and black is the absence of any color light. In the activity a prism is used to show that white light can be separated into its individual component colors. Also in the activity students discover that colored filters block some colors of light and allow others to pass through. If a red filters is placed in the path of a beam of white light, the beam will now appear red because the red filter only allows the red part of the

white light to pass through. This idea will become more apparent through the completion of the following activity.

Procedure: (Time required: 50 + minutes)

1. At least a day before the activity mix a batch of bubble solution. For strong, long lasting bubbles use equal parts Joy (dishwashing soap), glycerin (can be found at a pharmacy or chemical supply store), and distilled water. 2. As an introduction have the students blow bubbles and dip the wire frame shapes into the pre-mixed bubble solution. Ask the students the following series of questions: (Have the students write down their hypotheses, observations, and answers to the questions in their science notebooks.)  Ask the students to look through the bubbles. “Are the bubbles completely clear or can you see any colors present in the bubble?” (They should see many different colors from the spectrum)  Point out that the soap bubble solution is clear, but the bubble contains many different colors. “Where do you think the different colors are coming from?”  “If everything in the classroom was painted white, and you were all wearing white clothes, do you still think we would see colors in the bubbles?” (Tell the students that they are going to do an activity that will help them answer this question) 3. Have the students setup the equipment on each table or desk as shown in the diagram below. Setup the source of light at one end of the table. The prism should be placed on the desk a couple inches from the narrow slit in the black piece of construction paper. You may want to secure the piece of black poster board using silly putty as well. If you are afraid the putty will be taken, have the students hold the poster board. It should be positioned so that the light passing through the slit passes through the equilateral prism and on to a white piece of paper taped to an upright textbook on the other end of the table. Have the students follow the line of light from the prism on the surface of the desk or table in order to position the viewing paper. Position the upright text book so that a spectrum can be clearly seen on the white piece of paper

(as the textbook increases in distance from the prism the spectrum will become larger but dimmer). They should position the prism and textbook so that only one clear spectrum is visible.

**Note** Clear light bulbs must be used to produce a good spectrum, frosted bulbs will not work!!

**Caution** The light bulbs will get hot!

4. Have the students observe the light before it enters the prism by placing a small additional piece of paper in front of the beam before the prism. Now have the students observe the slit of light after it leaves the prism by observing the viewing paper taped to the wall (It was white light before it entered the clear prism, and now the light is broken up into many different colors after the light traveled through the prism). Where did the colors come from? The prism separated the white light into many different colors. 5. Using a pencil, have the students mark the edges of the band of colors on the white viewing paper and label the locations of the different colors, making sure that they don’t move the prism or the paper. 6. Demonstrate for the entire class, what happens when you place a colored filter in front of a white beam of light (using a flashlight), and shine it on a white piece of paper. 7. Have the students come up with hypotheses about what will happen to the different colored bands of light on the viewing paper if they place a colored filter in the path of the light before it enters the prism. 8. Have the students place different colored filters in the path of the slit of light, leaving the prism in its place. They should insert the filters into the path of the light before it enters the prism.  What happens when you put a red filter in the path of the light?  What happens when you put a blue filter in the path of the light?  What happens when you put a green filter in the path of the light? 9. Have the students record the results and comment on whether the results proved or disproved their previous hypotheses.  Based on the results of your experimentation, how do you think a filter works? (Sample Answer: A colored filter blocks/absorbs all colors of light except light that is the same color as the filter. Light that is the same color as the filter is allowed to pass through the filter and is projected onto the viewing paper. Without the use of a colored filter the entire spectrum is visible on the viewing sheet. If a red filter is placed in the path of the slit of “white” light, all of the colored bands on the

viewing paper disappear, except for the red portion of the line. A similar situation occurs when a blue filter is used, only the blue line remains on the viewing paper.)  What do you think would happen if you placed both a red and a blue filter in the path of the white light? If both filters were placed in the path of the light the red filter would filter out/absorb all of the other colors but red. Red light cannot pass through a blue filter, so the remaining light after passing through the red filter would not make it past the blue filter. Therefore, all of the colors on the white viewing paper would disappear. 10. Make sure all of the students understand that white light is made up of many different colors, that a prism can separate those colors, and that a colored filter only allows its color of light to pass.

Extension Demonstration: An overhead projector, a diffraction grating, and several different colored jars of water can be used as another demonstration / activity to allow students to investigate the nature of light, or it can be used to assess students’ understanding of the concepts covered in the previous activity. A diffraction grating can be purchased from a science supply store. You can purchase small card mounted diffraction viewers, or a larger diffraction grating film. A diffraction grating looks like clear plastic but it actually contains thousands of tiny parallel slits per inch. These parallel slits are able to separate white light into many different colors through the constructive and destructive interference of the light that passes through the slits. Placing either a small viewer or a larger diffraction grating film in the path of the light projected from an overhead will create a large spectrum on the viewing screen (Place two sheet of paper on the overhead projector so that they make one large vertical slit to allow the light to pass through). To demonstrate how colored filters can absorb certain colors of light, use glass jars with colored water as the “filters”. See if the students can predict what will happen when you place the colored water on the diffraction grating on top of the overhead projector. This will cause a large portion of the spectrum to disappear from the viewing screen.

Author: Aaron Debbink