Students will learn about light beams, the concept of refraction and bending.
Activity #1
Activity #2
Activity #3
Additional Resources
Books
Videos
Light rays slow down and may bend when they pass from one material to another. This bending is called refraction. Refraction happens because light travels at different speeds in different materials. Light changes its speed when it passes from one material into another. It travels at lower speeds through dense materials such as water and at higher speeds through materials that are less dense such as air. A beam of light will travel at a slower speed in a denser material. It will maintain that same, slower speed until it exits that material where upon it will resumes it original speed. (speed of light: in a vacuum: 186,000 miles/sec, air: slightly less than 186,000 miles/sec, water: 140,000 miles/sec, glass: 124,000 miles/sec, diamond 77,500 miles/sec)
Light refracts only when it hits another substance at an angle. When light impacts the boundary of another substance head-on (perpendicular or 90-degrees) it will slow down but will not refract. When light hits the substance at any other angle, it will refract. The angle of refracted light will increase in proportion to the angle of the entry. The angle at which the light crosses the media boundary and the angle produced after refraction is a very precise characteristic of the material producing the refraction.
Lenses are used to bend light. They are made of curved glass or other transparent material. Light always bends towards the thickest part of the lens. There are two types of lenses. A concave lens is thick on the outside ends and thin in the middle (think of a cave). A convex lens is thin on the outside edge and thick in the middle.
The electromagnetic spectrum (EM) is a name given to a group of different types of radiation. Radiation is energy that travels in waves through empty space as well as through air and other substances. The length of the wave determines the type of radiation energy it is. At one end of the EM are long, low-energy waves. These are radio and TV waves. At the other end of the EM are very short, high-energy waves which include x-rays and gamma-rays. Near the middle of the EM is a very small area of waves that we can see. This visible, white light is actually made up of all the colors. Each color has a different wavelength which is why our eyes are able to see the different colors. Red light has the longest wavelength (lower energy), and violet the shortest wavelength (higher energy). The Spectrum refers to this series of colored bands that can be seen when passing light through a prism. The major colors are: red, orange, yellow, green, blue, indigo, and violet. (ROY G. BIV)
Misconceptions to avoid:
1 Use Science Process and Thinking Skills.
4. Communicate Effectively Using Science Language and Reasoning.
Invitation to Learn
Students will experiment with various ways of magnifying objects;
After students have had time to try out the various magnifiers ask: What is happening? Why does everything look bigger?
Record their ideas on a K-W-L-H Chart -- even if they are incorrect. Later, as they discover new information, they can compare the K column (what we know) with the L column -- (what we learned). The middle column, What We Want to Find Out, will be used to record more ideas they would like to explore. These will be generated during class discussions. The H column is to be used for brainstorming How students could find the answers to their questions.
Instructional Procedures
Activity #1 Refracting Light -- a watery journey
Examples of analogies that illustrate light slowing down when entering another substance
Imagine pushing a shopping cart across a paved parking lot and onto a grassy area. If you push the cart straight onto the grass, it will slow down because the grass offers more resistance but it will continue in a straight line. However, if you push the cart at an angle onto the grass, the result will be different. If the front right wheel hits the grass first, it will slow down while the left wheel is still on the pavement. Because the left wheel is briefly moving more quickly it will cause the cart to turn to the right. When you move through the grassy medium and back onto the sidewalk on the other side, the wheel that hits the sidewalk will speed up causing the cart to turn in that direction.
Have each group come up with at least one analogy of their own to share. Have each student write their own analogies.
Presenting the Challenge:
Ask: Will different fluids refract light differently? Will the distance from the liquid to the focal point (where the light beams cross) be different? Will the size of the angles be different? Why do you think that? Refer to the sand analogy. Would a bike act differently in mud, gravel, etc? Have the class brainstorm different liquids they might want to try (dish soap, oil, honey, hand sanitizer, karo syrup, glycerin, etc.) Write their ideas in the W column of the K-W-L-H chart.
Planning the Inquiry
Talk about experimental design. If we are testing liquids, that is the variable. Everything else must be the same, otherwise we cannot be sure what is affecting the beams of light. Have students point out everything that needs to be the same (size and type bottle, quantity of liquid, distance of bottle from light source, and same flashlight). Review the steps that were taken in Activity #1. Tell students that scientists keep detailed, accurate records of their experiments so they can be duplicated. Students may use the Refraction Experiment Log--included at the end of this section--or they may design their own log.
Conducting the Inquiry
Students can be assigned to work in cooperative groups. Depending on time constraints, each group could either experiment with several liquids or each group would choose a different liquid from the list generated earlier and share their results with the rest of the class. Students could use the same paper they used for Activity #1. Use a colored pencil for the new liquid. It will make the comparison easier to see. Follow steps one through three in Activity #1.
Interpreting and Presenting Results
Each group should share their results with the class. If each group just tested one liquid, they could record their results on a large, class chart. A graph could be created which would show the relationship between the distance of the focal point (where the beams cross) from the bottle and the angle it makes.
Questions to consider: How do you know? What was your evidence? What makes you think this was true?
Students should be made to understand that their results and conclusions are valid for the materials they tested. Their sample was very small. Scientists might conduct hundreds of tests on hundreds of different kinds of materials before drawing conclusions.
Considering Implications for Future Research
An important part of the inquiry-based instruction is having students reflect on their activities. Consider the following: If you had to do it over again what would you do differently? Why? Did this inquiry raise new questions? Brainstorm what else we want to know. Write ideas on the K-W-L-H chart. What would happen if we: increased the size of the container? Changed the shape? Tried different temperatures? How did this activity show why scientific knowledge is always subject to change? Visit http://www.learner.org/jnorth/tm/inquiry/menu.html. This is an excellent site. A "Menu of Inquiry Strategies" includes lists of questions teachers could pose.
Activity #3 Refracting Light to Make Rainbows
Experiment with a variety of other ways to break up light into the pattern of colors called the spectrum.
Directions: Use a compass to make a four or five-inch circle on cardstock. Cut it out. The circle needs to be divided into seven equal sections -- the seven main colors of the spectrum. Point out how many degrees a circle is. Ask how do we figure out how many degrees each section will be? (51) Use a protractor to measure the sections. Color each section one of the colors of the spectrum. Color them in the correct order. Make a hole in the center of the disk. Push a pencil through and spin. (If you have an old phonograph turntable with adjustable speed, try spinning your disc on it.)
(Adapted from a lesson found at NASA's Stargazer website.)
Curriculum Extensions/Adaptations/Integration
For advanced learners:
There is an interesting explanation and demonstration of how "motion cards" work using refraction. (The pictures on motion cards change depending on the angle you hold them.) The How Stuff Works website is one good source of information.
For learners with special needs:
Post science objectives on a wall along with science words students should use. Have students work in pairs and groups. Strategies to help English Language Learners and other special needs learners are incorporated into this unit. They include: use hands-on activities, work in collaborative groups, model expected behavior and how to complete a task, provide real material to help make concepts concrete, prepare multiple forms of assessment, utilize graphic organizers, and minimize lecture format.
Family Connections
Look for objects at home that bend light and create rainbows or spectrum. One item to consider is, white light reflecting off beveled mirrors. (New vocabulary word--sloping or slanted). Some examples of faceted objects (many small surfaces) are pendants, cut glass bowls, diamond rings, CDs, soap bubbles, and spray from a hose.
Provide a list of websites and encourage families with computers and internet connections to explore some of these excellent sites, other families could visit a local library.
If you have a good color printer, print out one of the color charts from the internet, or find color charts at a paint store. Have students find examples around school and at home. Students might be given just one family of colors such as red and look for items that match the various shades (pink, rose, maroon, etc.).
Colburn, Alan. (2004) Inquiring scientists want to know. Educational leadership: Sep 2004, Volume 62.1, pp. 63-66.
Inquiry-based instruction is shown to be a realistic middle ground between hands-on verification activities and open-ended discovery learning. Colburn gives examples of how to take incremental steps in moving a bread mold verification activity towards a guided inquiry lesson. The crucial role of assessment is emphasized. This includes assessing the students' abilities to develop further questions to investigate.
Heber, Richard., Moore, Christopher J. (2002). A model for extending hands-on science to be inquiry based. Database: Academic search premier. Retrieved 12/11/2005.
Hands-on activities are typically presented as step-by-step instructions for students to follow to find a pre-determined answer to an assigned question. This model provides structure and guidelines for extending this traditional approach into a more valuable Strategies include: discrepant events to engage students in inquiry, brainstorming activities to facilitate planning investigations, written job performance aids, requirement for a product -- usually including a graph, class discussion and writing activities to facilitate student reflection.
May, David B., Hammer, David. (2004) Elements of expertise in the use of analogies in a 3rd-grade classroom discussion. AIP Conference Proceedings; Volume 720.1, pp. 149-152. EBSCO Host
Scientists regularly employ analogies to communicate their knowledge. Using analogies in the classroom, including those generated by students, has been shown to improve student conceptual learning. This article studies how one 3rd grader generated and used an analogy while engaging in an inquiry in a science lesson about earthquakes. The authors identify some of the elements of expertise in analogy use that can be taught.
Jensen, Eric. (2005) Movement and learning, Teaching with the brain in mind. ISBN 1-4166-0030-2
"The part of the brain that processes movement is the same part of the brain that processes learning." Jensen cites many studies and laboratory research showing the relationship between physical activity and increased cognition as well as better memory. In addition to providing for daily recess and physical education, Jensen makes many recommendations for how to incorporate physical activity into the daily curriculum.
Ways to build movement into the school day: