Light Waves Lesson Series
Light Waves
Introduction & Central Focus
By the turn of the 20th century, it was clear that the laws of motion do not apply to microscopic atoms and particles. Ernest Ruthorford’s experiments with the atom showed atoms are made of mostly empty space and that atoms do not comply with Newton’s laws. Physicists began working on a solution. They found that “at atomic scales, matter and energy were so tightly intertwined that their behavior mimicked each other, with astounding consequences” (Liu, “The Quantum Revolution” pg. 1). In 1900, Max Planck began the quantum revolution by creating the quantum model of light. Einstein built on Planck’s work through his work with the photoelectric effect. When light of varying wavelengths is beamed at metal, some wavelengths will cause electrons to be emitted from the metal while other wavelengths will not cause electron emission. The strength of the light beam does not matter. The wavelength does, however, because the shorter the wavelength, the higher the energy. For example, gamma rays have wavelengths of 0.01 nm and much higher energy than visible light with its wavelength around 1000 nm. Thus arose the dual nature of light; it acts as both a wave and a particle. (Liu, “The Quantum Revolution”)
Gamma and visible light waves are both part of the electromagnetic spectrum. All light on the electromagnetic spectrum travels at the same speed, and Einstein established this speed as the upper limit to the speed that anything can travel (“Applications: Einstein and Your CD Player”). The speed of light is constant no matter the frame of reference, which leads to some interesting implications. We know that time can speed up or slow down depending on the velocity of an object. The closer an object travels to the speed of light, the slower time goes. The length of an object and the mass of an object also change as speed approaches the speed of light.
Although this lesson series is not built around the concepts of time dilation, length contraction, or relativistic mass, the students will learn that all EM waves travel at the speed of light because they are forms of light. They will also work with the speed of light, wavelength, and frequency equation. Future lessons and science classes will build off this understanding.
In this lesson series, students will design and conduct an experiment using microwaves to measure either the speed of light or the wavelength of the microwaves emitted by the appliance. Essential questions include: What are the types of light? How is the speed of light measured? Why do all types of light travel at the same speed?
Define Learners
Grade: 8th
Population characteristics: The 8th grade class this lesson series is designed for is part of a rural Nebraska public school. This class of 35 students is broken into two sections for all core subjects, including science. The 8th graders have a range of reading levels and represent various levels of achievement in past science classes. Their 7th grade science class was integrated and included units in earth science, chemistry, and environmental science. In 7th science, they practiced collecting scientific data and learned basic chemistry concepts. Their 6th science class was life science. This year’s 8th science class is integrated, with units in genetics, evolution, space science, and physics. Students have one-to-one chromebooks and are experienced in completing group work. Three of the students have Individualized Education Plans (IEPs), with accommodations of extended time to work on assignments and tests and instructions read aloud.
Content Standards
Nebraska College and Career Readiness Standards: SC8.2.2.B Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.
CCSS.ELA-Literacy.W.8.1: Write arguments to support claims with clear reasons and relevant evidence.
Curricular Fit
This lesson will be during spring semester of 8th science when students are studying space science and physics. Specifically, it will be within a light waves unit of Amplify Science, the curriculum being used for 8th science. The topic will be taught following a lesson on how light carries energy that causes materials to change. During this preceding lesson, students will also be introduced to the field of spectroscopy.
In the days following this lesson series, students will learn about the harvest of light energy. Students will study how plants use light to make glucose during the process of photosynthesis and how different types of light affect materials in different ways.
Learning Objectives
SWBAT discuss methods of comparing light and mechanical wave speed.
SWBAT design an experiment using a microwave to measure the speed of light and the wavelength of waves produced by a microwave.
SWBAT explain, with evidence, that there are types of light beyond those they can see.
Materials & Resources
- Slinky
- Wave model
- Wooden dowels
- Round gummy candies
- Duck tape
- Camera phone
- Screen to project video
- Scrap paper
- Waves & the Electromagnetic Spectrum PPT
- The Speed of Light Lab
- Summative Assessment Rubric (Infographic & written paper)
Lesson Scope & Sequence
Timing | What the Teacher does | What the Student does |
Day 1: The Speed of Light 10-15 minutes: Hook/activate background knowledge 10 minutes: Discussion 15 minutes: Demonstration & direct instruction 5-10 minutes: Discussion & exit ticket | Introduce the light vs. sound waves activity to the students, and video the students while they are completing the activity. The activity is designed to activate prior knowledge and get students thinking about the speed of light. Play the video for the students and ask questions to start & continue the discussion:
Guide the students to the conclusion that light travels faster than sound. Show students waves with a slinky or create and use a physical model of a wave like the one shown in this video. Introduce the parts of a wave and the measurements we can take using this PPT: frequency, velocity amplitude, wavelength. Instruct students to have a table-group discussion on how we can measure the speed of waves, including the speed of light waves. Walk around to listen to each group, asking questions as needed to spur discussion. | Students will line up with a metronome at the front of the line. Then they will close their eyes and clap to the beat of the metronome as they hear it tick. Then they will open their eyes and clap using visual cues. Students will look at the video results and see that their claps were together during the visual cue but not during the metronome cue. They will discuss why this is the case. This discussion will partially fulfill the first objective of this lesson series because students will be comparing wave speeds: SWBAT discuss methods of comparing light and mechanical waves. Students watch the demonstration and think about how energy travels in waves. Students record the parts of a wave in their science notebooks and draw two models of how waves travel:
Participate in a small group discussion about how to measure the speed of waves, including the speed of light waves. Write down ideas on a slip of paper to turn in as an exit ticket. |
Day 2: The Electromagnetic Spectrum 10 minutes: Direct instruction & collect student ideas 25-30 minutes: Students design experiment 10-15 minutes: formative assessment | Introduce the electromagnetic spectrum to the students using the PPT. Ask the students once again how we might measure the speed of light using commonly available materials, guiding them with questions toward using the EM waves found in their houses and in school: the microwave. Listen for misconceptions (i.e. thinking mechanical waves fall on the EM spectrum). Introduce the lab and give directions for designing an experiment using a microwave to answer a student-generated question about the speed of light or wavelength of the waves produced by a microwave. Show this video to show one possibility for using a microwave. Most students will need guidance in creating a data table, so be prepared to guide the class through this step. Check students’ work so they are ready to run their experiments on day 3. | Students write down Electromagnetic Spectrum notes in their science notebooks and then brainstorm how we could measure the speed of light with the materials we have available inside the school. Students will answer pre-lab questions and design an experiment using microwaves to answer a question about the speed of light OR the wavelength of the waves produced by a microwave. This section of the lesson series will fulfill learning objective #2. Get experiment approved by the instructor before the end of class. |
Day 3: Light Experiments 35 minutes: run experiment 10 minutes: Check work & clean up | Prepare the microwave appliances in advance, and bring students to the location of the microwaves. Have a plan for how you will split time at the microwaves among the groups. Supervise the running of light experiments. Check students’ data tables as they are working, making sure they are set up for data-collecting success. Check all data tables. Supervise clean-up. | Students will run the experiments, doing at least three trials for every group. Students will be responsible for measuring and recording data in tables they created on day 2. In the experiment, the students measure the distance between melted spots on whatever food they have chosen (likely chocolate, marshmallows, or cheese), which is half the wavelength of the microwaves. Students will make sure all data is collected and then clean up their areas and put away supplies before class is over. |
Day 4: Data Analysis 15 minutes: Calculations 5-10 minutes: Analyze class data 30 minutes: Summative assessment | Ask students how to find the average, and write their answer on the whiteboard. Visit each group to check on their calculations. Create two large data tables on the whiteboard: the first for speed of light data and the second for light wavelength data. Instruct each group to add their data to the class table. Begin the final assessment. Hand out the rubric, and explain that the final assessment will be an argument that relates back to the introduction activity and the experiment. Students will answer the following questions using evidence from the experiment: Why do you see lightning before you hear it? Why can we use a microwave to measure the speed of light? | Students will do calculations and average their trial data to determine the approximate speed of the microwaves. Once individual groups have data, we will combine the data to determine a class average. With a greater number of trials, it is more likely that we will be closer to the actual speed of light. Then students will answer the post-lab questions. Students will begin the final assessment. They will create an argument to answer the following questions using the data from their group experiment and the class data: Why do you see lightning before you hear thunder? Why can we use a microwave to measure the speed of light? Students can express their argument in a written paper that follows a science report template and following the rubric, OR students can design an infographic using a free online tool, following the rubric as a guideline. |
Differentiation
Students will be divided into teacher-selected groups based on skill. Higher level learners will be able to help lower level students, and all will have a part in contributing to the group’s work.
Each student will be assessed individually at the end of the lesson series. Students can select their final product depending on which format they are most comfortable using. Papers are suitable for students who prefer expressing their ideas in written format that follows the format with which they will be familiar from past experiments, or students can create an infographic. The infographics are the more advanced option, as students will arrange important information in a way that has good flow and is organized and visually appealing. If the students have no experience making infographics, this will be a more advanced option for higher level students.
Final Assessment
The final assessment will be a written argument that relates back to the introduction activity and the experiment. Students will answer the following questions using evidence from the experiment:
- Why do you see lightning before you hear thunder?
- Why can we use a microwave to measure the speed of light?
Their final product can be a written paper or an infographic, depending on which format they prefer. The rubric is here.
Conclusion
This lesson is influenced by the American Museum of Natural History’s Seminar on Science course: Space, Time, and Motion. Specifically, it is built around the lessons on Einstein’s theory of special relativity and Einstein’s work with the photoelectric effect. The goal of this series is to help 8th grade students learn about the types of light beyond the visible spectrum that vary in energy and wavelength and to help them understand that all light waves travel at a constant speed, no matter the wavelength.
The first lesson’s activity activates students’ background knowledge of the relative speed of light and sound waves. Students will also participate in discussions about speed of light and light versus sound waves. Designing the experiment will be the most difficult part of the lesson series for the students, but they will see an example of one possible experiment design and will have teacher and peer guidance. The choice of final project product will differentiate the assessment for various levels of learners.
Before and during the experiment, students will create a model of how waves are transmitted and absorbed through various materials, a Nebraska College and Career Readiness Standard in Science. In their notes, students will sketch a models of energy moving through a slinky and energy being emitted from a radiant heat source. In the post-lab questions, students will draw a model of microwaves being absorbed by the food source they used in their experiment. In the final assessment, students will use their experiment data to make an argument based on evidence, meeting a Common Core literacy standard. They will make a claim with evidence as to why lightning is heard before thunder, and they will argue that microwaves are a type of light, even though we cannot see this type of light. Students will come away from this lesson with a better understanding of the electromagnetic spectrum and a background sufficient to move into the next lesson about the harvest of light energy.
References
Dr. Charles Liu. “The Quantum Revolution.” American Museum of Natural History Seminars on Science: Space, Time, and Motion.
Dr. Charles Liu. “Applications: Einstein and Your CD Player.” American Museum of Natural History Seminars on Science: Space, Time, and Motion.
Amplify Science curriculum: Grade 8, “Light Waves” unit
Exploratorium Teacher Institute. “The clapping speed of sound.https://www.youtube.com/watch?v=K_ab2cOQQ1Y
“Sound & light travels in waves” https://www.youtube.com/watch?v=sB8w2FvPsBA
UGA Extension. “Measuring the speed of light with chocolate.” https://extension.uga.edu/content/dam/extension/programs-and-services/science-behind-our-food/documents/MeasuringSpeedLightChocolate.pdf
Jefferson Lab. “Measure the speed of light - with chocolate!” https://www.youtube.com/watch?v=7WXW2bBWBEg
Rubistar. http://rubistar.4teachers.org/index.php
Morgan Park High School. “Infographic Rubric.” https://www.morganparkcps.org/ourpages/auto/2015/2/.../infographic%20rubric.doc