5 Wavelength And Color

Light & Optics Unit Becky McCoy

Lesson Title: Wavelength and Color Timing: 50 Minutes (can be extended to 2 classes) Target Audience: High School Conceptual Physics Course (9th – 12th grade)

Objectives: Students Will Be Able To: • Determine the wavelength of the colors of light experimentally. The Teacher Will Be Able To: • Provide students with mathematical reasoning behind color.

Standards Assessed: New York State, The Physical Setting 4.3 i. compare the characteristics of two transverse waves such as amplitude, frequency, wavelength, speed, period, and phase

Misconception(s) Addressed: • •

Colored light mixes like colored paint. Color is an inherent property of an object.

Prior Knowledge: Content from previous lessons in the unit.

Aim: Experimentally learn more about the wavelengths and colors of light. Concept Map Vocabulary: • • • •

Wavelength Color Visible Light Spectrum

Necessary Preparation: COPIES • Coloring Physics MATERIALS • Diffraction Gratings • Flashlights, Lasers, or other light sources • Blank wall or screen • White paper SET UP

• • •

Diffraction Diffraction Grating Prism

Light & Optics Unit Becky McCoy

Lesson Plan

Aim: Experimentally learn more about the wavelengths and colors of light. Physics Push-Up: Coloring Physics (5 minutes) Handout the Coloring Physics sheets and crayons. Be sure to have red, orange, yellow, green, blue, and purple colored crayons.

Activity: Finding the Wavelength of Colored Light (15 minutes) Materials: • Diffraction Gratings • Flashlights, Lasers, or other light sources • Blank wall or screen • White paper Procedure: 1. Shine the flashlight (monochromatic light) against the wall or screen. 2. Have students describe the light. 3. Shine the light through the diffraction grating and have students describe what has changed about the light. 4. Break students into smaller groups and give each a diffraction grating, light source, and blank piece of white paper. 5. Students should shine the light source through the diffraction grating so they can see a rainbow pattern. 6. Students should measure the distance from the light source to the paper. 7. Students can color the bands of color with appropriately colored markers so they can measure the distance between the like colored marks on the paper. 8. Students now use the equations they learned last class to determine the wavelength of each color of light.

Activity Summary: Mixing Colors (20 minutes) Write the accepted values for the wavelengths of color on the board. Have students fill in the wavelengths they found in the experiment in the rainbow. Talk about how mixing paint/crayon colors is different than mixing light. Mixing colors of light can be illustrated through the diagram below or by bringing in colored light filters to show students what happens when two colors of light are added together. If students show keen interest, are struggling with this concept, or needed extra time for the experiment, extend this lesson into two lessons. Use this discussion on mixing colors to transition to superposition and interference, which could be considered a discussion on “mixing” or “colliding” waves.

Light & Optics Unit Becky McCoy This picture is a great illustration of what happens when you mix the colors of light, which is very different than when you mix the crayon colors, as in the Physics Push-Up. Red, green, and blue make white (monochromatic light). Combining any two colors of light make a secondary color of light: Red + Green = Yellow Green + Blue = Cyan Blue + Red = Magenta http://www.diycalculator.com/imgs/console-09.gif

These secondary colors are the colors used in printing. Students can look at a color ink cartridge and see this. When the secondary colors are added together, they make black (as in printing). When any two secondary colors are mixed, they create the primary color of light they share. For example, blue light is used to make magenta and cyan light, so Magenta + Cyan = Blue.

Homework: Error Analysis (5 minutes) Students should look up the accepted values of wavelengths of color and compare the results they got in class. This comparison should be completed in written form, including an error analysis. The procedure of error analysis will have been covered at the beginning of the year so that students understand how to calculate percent error as well as estimate uncertainty. Final project proposal due next class.

Exit Strategy: Project Check-In (5 minutes) Each student should tell the teacher how they are planning on representing what they have learned in their Final Project.

Extension Activity: As suggested in the Activity Summary section, show students how the colors of light add together using colored light filters.

Assessment: • •

Student questions and discussions throughout class. Error analysis homework.

Resources: Reasoning in Physics: The Part of Common Sense by Lawrence Viennot

Notes & Adaptations:

Light & Optics Unit Becky McCoy Name __________________________________________________ Date _________________

Coloring Physics Using the crayons, color in the rainbow.

Using the primary colors – red, blue, and yellow – color in the three circles. Make a note of what colors are made when two or three colors overlap, what colors are made?