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The Bending and Bouncing of Light
Author: Joyce Brumberger
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As a result of the presenter-conducted module, participants will learn about the transfer of light energy as it interacts with matter. Key terms of refraction and reflection will be explored as they apply to light energy. Participants will design a lesson they can implement in their own classroom.
- Participants will learn the definition of the terms reflect and refract as they apply to light energy.
- Participants will learn the difference between reflection and refraction.
- Participants will learn about the relative index of refraction of common substances.
- Participants will be able to provide examples of reflected and refracted light.
- Participants will be able to create lesson plans for the concept of reflected and refracted light.
- Clear Plastic Drinking Cups - 8 oz. or larger
- Vegetable oil
- Mirrors - sizes may vary, but one size must fit inside a cup or container for the exploration phase
- Tennis balls
- 8 1/2" x 11" paper
- Transparency, cut in pieces
- Permanent marker
- Ghost crystals (Ghost Crystals can be ordered from Flinn Scientific, Inc.(800/452-1261) or Educational Innovations, Inc. (888-912-7474))
- Distilled water
- Clear plastic containers, quart size
- Ask participants to look at a glass of water with a pencil in it and have them draw their observations. Tell them to look at the glass from all angles.
- Ask them to explain their observations and hypothesize the cause of this discrepant observation. (The pencil will appear to be bent in the water even though the pencil is actually straight)
- Add vegetable oil to the glass of water and have participants observe and illustrate their observations. (The pencil will appear to be bent to an even greater extent in the oil layer when observed through the side of the glass.)
- Ask participants to explain their observation and hypothesize the cause of this discrepant observation. (Answers will vary. Accept all reasonable answers.)
- Ask participants if they would be able to observe the same phenomena if the room was dark and ask them to explain their answers.
Based on common experience, most participants will answer that objects cannot be seen without light. Explanations of their answer will vary.
Assessment: Assessment is ongoing as participants record observations and ideas as well as respond orally during the Engagement phase.
- Working with partners or small groups, ask participants to shine a flashlight straight towards a wall and observe the light from the flashlight as well as the light on the wall. Observations should be recorded and illustrated.
- Tell one of the participants to put a mirror straight in the middle of the light path between the flashlight and the wall. Record observations. (Do not shine light in anyone's eyes.)
- Instruct the participant holding the mirror to hold it at an angle in the path of light. Record observations.
- Tell the participant to take a tennis ball and throw it straight at the wall and observe what happens.
- Tell the participant to throw the tennis ball at an angle to the wall and observe what happens.
- In a darkened room, have participants shine a flashlight straight down into a glass half-filled with water. Ask them to illustrate and orally describe their observations.
- Tell participants to shine the flashlight at an angle to the surface of the water. Ask them to illustrate and orally describe their observations.
- Tell participants to place a mirror at the bottom of the glass and shine the flashlight at an angle. Ask them to illustrate and orally describe their observations.
Assessment: The professional development provider can assess participants understanding through oral explanations and written observations and drawings.
To get a formal definition of key terms.
- When you see yourself in the mirror or other shiny surface, what is the word that describes this experience? Answers may vary. The key term is reflection.
- When an object seems bent or distorted like mirrors at a carnival, what is the word that describes this experience? Answers may vary. The key term is refraction.
- Using the two key terms, what term best explains what happened to the ball when it hit the wall at an angle? It was reflected.
- What is the term that explains what happened to the light when the pencil appeared bent in the glass of water? The light was refracted.
- Based on your observations, which material bends light more: water or oil? The oil refracted the light more so the pencil appeared very bent as compared to the water. At this time, the concept of index of refraction should be discussed on relative terms. When a substance bends light more than another, it is said to have a higher index of refraction. Oil has a higher index of refraction than water or air.
Assessment: Participants' responses to key concepts and their responses to additional examples.
- Tell participants to shine a flashlight a short distance away from a prism. A partner should hold a white sheet of paper a short distance on the other side of the prism.
- Ask participants to illustrate and orally explain their observations using proper key terms.
The light from the flashlight will bend as it goes through one side of the prism and out the other. This bending of light is call refraction and will result in the light bending into different wavelengths of light displaying a rainbow (spectrum) of color. The pattern always displayed is ROYGBIV; red, orange, yellow, green, blue, indigo, and violet. The longest and slowest wavelengths are red and the shortest, fastest wavelengths of light are violet.
- The Professional Development Provider will distribute to participants prepared containers of hydrated ghost crystals.
- Tell participants to pour water into the container until they can read the "secret message".
- Ask participants to explain how the message was revealed using correct key terms. Ghost crystals have the same index of refraction as water. Refer to the "Explanation of the Science" section for further information.
More detailed information on science inquiry can be found at: https://uakron.edu/polymer/agpa-k12outreach/best-teaching-practices
NSES Standard A: Science as Inquiry: As a result of activities in grades 5-8, all students should develop abilities necessary to do scientific inquiry
- Design and conduct a scientific investigation
- Develop descriptions, explanations, predictions, and models using evidence.
- Think critically and logically to make the relationships between evidence and explanations.
- Recognize and analyze alternative explanations and predictions.
- Communicate scientific procedures and explanations
NSES Standard B: Physical Science: As a result of their activities in grades 5-8, all students should develop understanding of transfer of energy.
- Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei and the nature of a chemical. Energy is transferred in many ways.
- Light interacts with matter by transmission (including refraction), absorption, or scattering (including reflection). To see an object, light from the object - emitted by or scattered from it - must enter the eye.
- The sun is a major source of energy for changes on the earth's surface. The sun loses energy by emitting light. A tiny fraction of that light reaches the earth, transferring energy from the sun to the earth. The sun's energy arrives as light with a range of wavelengths, consisting of visible light, infrared, and ultraviolet radiation.
NSES Standard G: History and Nature of Science: As a result of activities in grades 5-8, all students should develop understanding of Science as a human endeavor
- Science requires different abilities, depending on such factors as the field of study and type of inquiry. Science is very much a human endeavor, and the work of science relies on basic human qualities, such as reasoning, insight, energy, skills, and creativity, as well as on scientific habits of minds, such as intellectual honesty, tolerance of ambiguity, skepticism, and openness to new ideas.
NSES PROFESSIONAL DEVELOPMENT STANDARD A: Professional development for teachers of science requires learning essential science content through the perspectives and methods of inquiry. Science learning experiences for teachers must:
- Involve teachers in actively investigating phenomena that can be studied scientifically, interpreting results, and making sense of findings consistent with currently accepted scientific understanding.
- Address issues, events, problems, or topics significant in science and of interest to participants.
- Introduce teachers to scientific literature, media, and technological resources that expand their science knowledge and their ability to access further knowledge.
- Build on the teacher's current science understanding, ability, and attitudes.
- Incorporate ongoing reflection on the process and outcomes of understanding science through inquiry.
- Encourage and support teachers in efforts to collaborate.
NSES PROFESSIONAL DEVELOPMENT STANDARD B: Professional development for teachers of science requires integrating knowledge of science, learning, pedagogy, and students; it also requires applying that knowledge to science teaching. Learning experiences for teachers of science must:
- Connect and integrate all pertinent aspects of science and science education.
Best Teaching Practices
- Learning Cycle
- Science Process Skills
Two 40 minute sessions.
- Ghost crystals - the suggested proportions are 2 tbsp. of crystals to 1 gallon of water. Mix in a large container the day before to allow full hydration.
- Cut transparencies to fit the size of the quart size plastic container. With a permanent marker, write a message on the transparency which could be school related, a holiday greeting, or simply "Ghostbusters!"
- Insure flashlights are working and have fresh batteries
- Water and oil mixture - oil should be drained out of the cup in a separate container and can be reused. Remaining water can be disposed of down the sink.
- Flashlights should never be shined towards anyone's eyes.
- Goggles should be worn when bouncing the tennis balls.
- Ghost crystals or non-toxic, but still should not be ingested. Place hydrated crystals in an open container to dry. They can be reused many times.
Assessments are ongoing throughout the learning cycle.
Teachers convert a teacher directed science activity into an inquiry-based lesson plan for their students.
Explanation of Science
Light is a type of electromagnetic radiation which travels in the form of waves. Most natural light comes from the sun and travels though the vacuum of space transferring potential energy to kinetic energy when the wave interacts with a medium that causes the material to move. Waves behave in predictable ways and have measurable properties.
When light reaches matter it can be reflected, refracted, absorbed, or scattered. Light bouncing back off a surface is reflected light. Shiny surfaces commonly reflect light. When light travels from one medium to another it bends or is refracted because waves travel at different speeds through different medium. The extent to which it bends is called the index of refraction. The higher the index of refraction, the more the light bends. Water has a higher index of refraction than air, as evidenced by the pencil in the glass of water. Materials have designated indexes of refractions based on measured values and calculations.
Ghost Crystals is a common name referring to a super absorbent polymer called polyacrylamide. It is not to be confused with sodium polyacrylate, which also has super absorbing characteristics, but is chemically different. Sodium polyacrylate is the substance found in disposable diapers while polyacrylamide is commonly found in gardening supply stores for moisture retention in soils.
When hydrated with distilled water, the polyacrylamide crystals absorb about 40-200 times their weight. A hydrated crystal contains so much water that when placed in a container of water light passes through it with out becoming distorted or bent. In fact, the crystal seems to disappear. However, when the crystal is in the air, light is refracted because the speed of light through the air is different than that through the crystal, which remember, is comprised mostly of water. It is the same phenomenon as the pencil in a cup of water.
Index of Refraction
Use different materials in a cup containing a pencil to observe variations in the index of refraction. Some common materials and their refractive indices can be found under References.
Loop a string of thread around a ghost crystal and carefully tie a knot. Suspend the crystal from a pencil and immerse it in a glass of water. Only the string will appear.
Research metamaterials. They are relatively new materials that cause light to go backwards.
Lesson Implementation Template
Download Lesson Implementation Template: Word Document or PDF File
Try to insure that all participants have participated and expressed their ideas either verbally or through written comments or illustrations. When working in pairs or groups try to make the groups as heterogeneous as possible being sensitive to specific needs of individuals.
None available for this module