Reflection, Refraction, Absorbtion, and Diffusion (Denise Noah)

Title: Moving Light

Principle(s) Investigated: How light travels through a variety of mediums

Standards: MS-PS4-2: 8th grade: PS4.B: When light shines on an object it is reflected, absorbed, or transmitted through the object depending on the object's material and the frequency of the light; The path that light travels can be traced as straight lines, except at surfaces between different transparent materials, such as air and water or glass and air, where light bends; A wave model of light is useful for explaining brightness, color, and frequency-dependent bending of light at surfaces between media. (CCC: structure and function, patterns SEP: asking questions, building models, constructing explanations, engaging in argument from evidence)

Materials: Clear glass of water, empty clear glass, spoon, pen or pencil, mirror, prism, black construction paper, plain white paper, flash light from cell phones, old cd's (everything is available at a store like 99cent stores or Target except the prism which can be ordered through science educational supply stores such as: https://www.schoolspecialty.com/delta-education-large-prism-160-4668gclid=Cj0KCQjwwODlBRDuARIsAMy_28W1SQRLNA3KZbOgIWCdTO71OW3xc9h4nhGBRpnaic7kZpJhqutoDxIaAobOEALw_wcB)

https://docs.google.com/spreadsheets/d/1J6V7AyfBfCZL5JWW5JM6XpB5aLMVzXTh3sgk7rATPas/edit?usp=sharing

Procedure: Teacher sets the goal: Students will be able to create a model that describes the different ways lightwaves can travel through different mediums. Scaffolding for ELL's: Define medium: an intervening substance, (in this phenomena, something in between your eye and the lightwaves being transmitted) Define transmission: act of moving something from one place to another. Define frequency: The number of times an event occurs per unit of time. Define absorbtion.

Engage: Introduction of phenomena: spoon seen through a glass of water when looking at it through the side; T: What do you notice? (Google sheets responses by students) Where does the break in the spoon appear? (Google sheets responses by students)

Explore: Teacher asks students to explore whether the spoon ever looks normal as seen through the glass of water? At what angle? (Google sheets response) Students then explore looking at a pen or pencil and writing on a paper through the glass of water. What do they notice? (Google sheets responses)

Explain: Teacher asks students, in small groups of 2, to draw a model of what might be occurring to the light waves to cause the phenomena. Scaffolding: Teacher asks students what mediums the light from the spoon is traveling through in this phenomena prior to their creating models. Students share their teamwork on the projector. Based on their models, what can students infer using inductive reasoning? (Google sheets responses) Teacher asks students if light behaves this way for mediums other then water and air? Teacher asks students to look through the empty glass bottom at the spoon or pen, moving the object a variety of distances from the glass. What do they observe? (google sheets responses) Teacher asks students to make a model for this phenomena. The models are shared. What can be inferred?

Explore: Teacher asks students to look at mirrors from all angles. What do they notice? Teacher asks students if they have any questions about this phenomena. (If facilitation is needed, provided by teacher)

Explain: Students work in groups to draw a model of how this might occur. The models are shared and discussed. Teacher brings up analogies for reflection (a ball bouncing) and refraction (a skateboard on cement suddenly veering and changing direction because it moved onto grass)

Extend: Teacher asks students to respond on google sheets how does reflection affect us in everyday life? How does refraction affect us in everyday life? We see our reflections in mirrors because of reflection, we can see things in rooms even though the light is not traveling straight from the sun directly into our rooms because of reflection and diffusion.

Closure: What did you learn?

Student prior knowledge: Light can travel as a wave or as a particle carrying energy (photon); When light travels as a wave, it has a wavelength measured from the trough to trough or peak to peak.

Explanation:

Snell's Law: Refraction of light is caused by the difference in speed of light in different media.For example,the speed of light in air is approximately 3.0 × 10⁸ ms^-1 ,however when light travels through a medium,such as water or glass,its speed decreases.The speed of light in water is approximately 2.3 × 10⁸ ms-1,while in glass,it is approximately 2.0 ×10⁸ ms^-1. To describe the change in the speed of light in a medium,we use the term refractive index and the angle of incidence.

See the equation if you know the angle of light and the refractive index: https://www.youtube.com/watch?v=HlbPdFDmwyg

Also: https://en.wikipedia.org/wiki/Snell%27s_law

In reflection of light, the angle of incidence is equal to the angle of reflection.

Reflection angles: https://www.physicsclassroom.com/class/refln/Lesson-1/The-Law-of-Reflection

We see color because the other wavelengths of visible light have been absorbed, and only the visible wavelength of the color we see is passing through.

Diffusion is light bouncing off of rough objects in all angles. There is no image reflected because the light is scattered in every direction.

Questions & Answers: 1. Why does the spoon look broken at the surface of the water? As light travels through the water, it appears to travel at a different speed then through the air, and the light bends. It is similar to a skateboard moving on cement and then suddenly hitting grass. The front wheels will turn and change the direction of the board. The light waves bend. 2. Why does the mirror reflect images that are not just in front of it, but are off to the side? The light within the room is diffused everywhere. Some of it hits the mirror at an angle, and it is reflected off the mirror at the same angle in the opposite direction. It is similar to a ball bouncing, the angle of incidence is equal to the angle of reflection. 3. What causes the colors of sunset? The light is being refracted off of dust and other particles in the sky. As the light moves at different speeds, different colors appear, just as in a rainbow.

Applications to Everyday Life: We see our reflections in mirrors because of reflection, we can see things in rooms even though the light is not traveling directly into our rooms. The light enters our rooms because of reflection and diffusion as the light bounces off of dust particles and other matter outdoors; Reflection is used in creating telescopes. Refraction is used for creating eye-glasses, microscopes, and some binoculars and telescopes. It is also the reason we see rainbows in the sky or through prisms. Absorbtion allows us to create different colored artworks, clothing, and other objects because the colors we see are the colors not absorbed.

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