Light Energy. Countdown: Experiment 1: 1 tomato paste can (without top or bottom) table lamp white poster board, 7 x 9

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1 Light Energy Grade Level: 5 Time Required: 1-2 class periods Suggested TEKS: Science Suggested SCANS: Information. Acquires and evaluates information. National Science and Math Standards Science as Inquiry, Life Science, Earth & Space Science, Physical Science, Measurement, Reasoning, Observing, Communicating Countdown: Experiment 1: 1 tomato paste can (without top or bottom) table lamp white poster board, 7 x 9 pencil wax paper (small piece) scissors aluminum foil (small piece) 2 rubber bands straight pin Experiment 2: flashlight 1 white poster board 3 x 5 small flat mirror various materials (i.e., fabric, aluminum foil, wax paper, different color poster board, etc. to test for light reflection) Experiment 3: pencil glass of water Experiment 4: 8 toothpicks 8 raisins 1 bowl of soapy solution 1 short piece of string Activity: 1 (3 x 5 ) index card 1 pencil stapler Ignition: Two basic forms of energy through which we experience our world are light and sound. Both have their own special qualities. Light is energy that we can see. Light travels as waves, like ripples on a pond. But not all the waves are the same size. Some waves are short, while others are long. When we observe 78

2 colors, we are seeing light of different wavelengths. The light of the sun appears to be colorless, as it is called white light. It is, however, a mixture of many colors of light. When a rainbow appears in the sky after rain, you can see some of these colors. As sunlight is reflected through raindrops, it is bent, or refracted. Light with long wavelengths like red is bent more than light with shorter wavelengths, like violet. For this reason, the colors fan out into a rainbow as they reemerge from a raindrop. Also, light waves travel in straight lines. If they hit an object in their path, three things might happen: 1) Some of the light waves pass through the object and are transmitted (as with a transparent glass window). 2) Some of the light waves bounce off the object and are reflected (as with a mirror). 3) Some of the light waves are trapped by the object and are absorbed (as with the opaque green leaves of a plant). Light travels much faster than other kinds of waves, at a speed of about 300,000 kilometers per second. In one second, a wave of light can travel around the earth 7 times. Additionally, light can move through a vacuum. This means that astronauts on the moon s surface can see and photograph each other, even though there is no air on the moon. This does not hold true, however, for sound. Astronauts must depend on radio waves rather than sound waves to communicate on the moon. Liftoff: A. Experiment 1 - Do light waves travel in straight lines? 1. Stand the tomato can in the center of the poster board and trace it. Cut out the circle that you ve traced. 2. Place the wax paper over 1 end of the can, and secure it firmly with a rubber band. Place the aluminum foil over the other end of the can; secure it with a rubber band. 3. Use the straight pin to carefully make a small hole in the center of the aluminum foil. 4. Push the can through the hole in the poster board. 5. Make the room as dark as possible. Facing the lighted lamp, hold the poster with the can in it, as shown below. Aluminum Foil Waxed paper Lamp 50 cm Poster Board 6. Move the poster board closer to or farther away from the lamp until you can see the bulb image clearly on the wax paper. 7. Answer the following questions: a. How is the image on the paper different from the light bulb? 79

3 b. What are the paths of the light waves from the top and bottom of the bulb to the top and bottom of the image? c. Do light waves travel in straight lines? B. Experiment 2 - How do different surfaces reflect light? 1. Test how well a mirror reflects light. Set up the experiment, according to the diagram below. Shine the light on the mirror in a dark room. The light that is reflected upon the white poster should be almost as bright as the flashlight beam itself. 2. Test how well different kinds of materials reflect light. Do the same experiment as for #1, except put the new material in the place of the mirror. (You may prefer to drape the material over the mirror, and then shine the light on it.) Observe the differences of reflection for each. Mirror White Poster Piece Flashlight (turned on) C. Experiment 3 - Can the direction of a light wave change? 1. Place a pencil in a glass of water. Notice that the pencil appears bent, or refracted. See diagram below. The speed of light changes slightly as it moves from one material (water) to another (air). Therefore, the light waves change direction, causing the illusion of a bent pencil. Pencil Air Water D. Experiment 4 - Can you make colored bubbles? 1. Make a square by using 4 toothpicks as sides and 4 raisins as vertices. 2. Loop the string through a toothpick side, and dip the square into soapy water. Gently pull it out notice the 2-D bubble that s been formed. 80

4 String Toothpick 3. Make a cube by using 8 toothpicks as sides and 8 raisins as vertices. 4. Carefully, loop the string through a toothpick side, and dip the cube into soapy water. Pull it out, notice the 3-D colored soap bubble that formed. Light rays reflect from both the outer and the inner surfaces of the bubble. A ray that is reflected from the inside must travel slightly farther than one that is reflected from the outside, so when the waves meet they are slightly out of step. Some colors cancel out and disappear, others combine to make bands of color on the surface. Raisin String E. Activity - Making a Thaumatrope Movie 1. Get one 3 x 5 index card, and cut it in half horizontally. Draw a big shark on the left side of the first card. Then, draw a small fish on the right side of the 2 nd card. Large Shark Small Fish 81

5 2. Put the 2 cards together, with pictures facing toward the outside. Slide a pencil, eraser first between the cards and staple in place. See diagram below. Pencil on the inside 3. Hold the pencil between your palms. Roll it back and forth quickly. Notice that the shark is eating the little fish. 4. Make different movies with different stories, i.e., a cat sitting in a wastebasket and a speeding gorilla chasing a car. 5. Explain to the students that our eyes remember things. For a split second, they hold onto the last image that they ve seen. If we quickly replace the object with another, we will see both images together. It is eye/brain memory that makes movies and cartoons work. F. Activity - Comparing Ordinary Light to Laser Light 1. Ask students to research laser light to answer the following questions: a. What is laser light? b. How is laser light different from ordinary light? c. How is laser light generated? d. What are the applications of laser light in modern day technology? 2. Using the information located, students should then organize it into a Venn Diagram, as below: 82

6 Ordinary Light Laser Light 83