The Bending and Bouncing of Light
Author: Joyce Brumberger
Students will learn about the transfer of light energy as it interacts with matter. Key terms of refraction and reflection will be explored through hands-on inquiry. The science of the formation of rainbows will also explored.
What should students know as a result of this lesson?
- definition of the terms reflect and refract as they apply to light energy
- difference between reflection and refraction
- relative index of refraction of common substances
What should the students be able to do as a result of this lesson?
- provide examples of reflected and refracted light
- identify the behavior of light as either reflected or refracted
- 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 students 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 students 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 students to explain their observation and hypothesize the cause of this discrepant observation. (Answers will vary. Accept all reasonable answers.)
- Ask students 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 students will answer that objects cannot be seen without light. Explanations of their answer will vary.
Assessment: Assessment is ongoing as students record observations and ideas as well as respond orally during the Engagement phase.
- Working with partners or small groups, ask students 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 students 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 students shine a flashlight straight down into a glass half-filled with water. Ask them to illustrate and orally describe their observations.
- Tell students to shine the flashlight at an angle to the surface of the water. Ask them to illustrate and orally describe their observations.
- Tell students 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 students 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: Students' responses to key concepts and their responses to additional examples.
- Tell students 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 students 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 students prepared containers of hydrated ghost crystals.
- Tell students to pour water into the container until they can read the "secret message".
- Ask students 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.
Best Teaching Practices
- Learning Cycle
- Science Process Skills
Alignment with Standards
- MS-PS4-1 Use mathematical representations to describe a simple model for waves that includes how the amplitude of a wave is related to the energy in a wave.
- MS-PS4-2 Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.
Common Core Standards:
- RST.6-8.3 Follow precisely a multistep procedure when carrying our experiments, taking measurements, or performing technical tasks.
- WHST.6-8.9 Draw evidence from informational texts to support analysis, reflection, and research.
- Content Standard A: 5-8 Science as Inquiry
- Content Standard B: 5-8 Physical Science
- MContent Standard G: 5-8 History and Nature of Science
- Grades 6-8 Earth and Space Sciences Benchmark C
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.
- 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 are non-toxic, but still should not be ingested. Place hydrated crystals in an open container to dry. They can be reused many times.
Sight is one of the five senses. Understanding how we see the world around us begins with exploring light's behavior when it reaches various surfaces. Seeing a reflection in a pond or a rainbow are phenomena that can be understood with the study of the reflection and refraction of light.
Ongoing throughout learning cycle.
Grouping Suggestions: Try to insure that all students 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.
Pacing/Suggested Time: 45 minutes to an hour
Printable PDF Worksheets
None available for this lesson.