The Arizona STEM Acceleration Project

Light Reflection and Light Refraction

Light Reflection and Light Refraction

An 11th and 12th Grade STEM Lesson

Donna Brunjes

March 2024

Notes for Teachers

• Context: This lesson takes place first in a classroom then in a lab for two consecutive days for approximately one hour per day.
• Students work in small groups of 2-4 students each.
• This lesson demonstrates the properties of light reflection and light refraction.
• Students should have prior basic knowledge of transverse waves (light waves) and electromagnetic radiation.
• Students use math skills to calculate speed of light and light refraction word problems.
• Teacher explains applications of light reflection and light refraction in modern technology.

List of Materials:

• Review of light (transverse) waves’ speed, frequency and wavelength, and how these variables are related and calculated
• Introductory lesson/assignment on how light can be transmitted through various mediums and materials
• Examples of light reflection and light refraction, the differences between these two types of light transmissions, and how they are currently used in modern technology
• Snell’s Law Overview and Word Problems
• Glass lenses (with different magnifications) and prisms
• Convex and concave mirrors
• Laser pointers and white-light flashlights
• Tall drinking glasses
• Blank white paper and colored markers
• Plastic multi-colored straws
• Team Lab Data Collection and Question Sheet

Arizona Standards

Science Standard:

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HS.P4U1.10: Construct an explanation about the relationships among the frequency, wavelength, and speed of waves traveling in various media, and their applications to modern technology.

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Science and Engineering Practices for High School:

• Developing and Using Models
• Analyzing and Interpreting Data
• Using Mathematics and Computational Thinking
• Planning and Carrying Out Investigations
• Obtaining, Evaluating, and Communicating Information
• Constructing Explanations and Designing Solutions
• Engaging in Argument from Evidence
• Asking Questions and Defining Problems

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Objective(s):

Today we review how the speed of light in a medium is determined by the frequency and wavelength of the light wave. Next, we will explore how light can travel through various mediums and materials, and how its speed varies as a result.

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Objective(s) (continued):

Then we will learn about light transmission via reflection and refraction. Reflection occurs when light rays bounce off the surface of a medium without penetrating that medium. Reflections are either specular (via a smooth surface) to produce a clear image, or diffuse (via a rough or irregular surface) which causes the light rays to scatter in different directions. Mirrors, for example, work on the principle of reflection.

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Objective(s) (continued):

Refraction occurs when light passes from one medium to another with a different refractive index. Light rays will bend or change direction because light travels at different speeds through different mediums. Light wavelengths also change in proportion to the speed change. Snell’s Law is a formula used to calculate angles and refraction indices for light rays. We will use Snell’s Law to calculate different light refraction problems entailing different mediums. Lenses, for example, work on the principle of refraction.

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Objective(s) (continued):

Tomorrow we will explore through hands-on activities how light can be reflected or refracted. We will first explore the principles of light reflection by using convex and concave mirrors, and calculating the angles of specular and diffuse reflections on different surfaces.

Next, we will use glass lenses, prisms, laser pointers, flashlights, drinking glasses filled with water, plastic straws and drawings on paper to explore the many facets of light refraction.

Each team of students will collect data from their hands-on activities, answer questions to explain the relationships among the frequency, wavelength, and speed of light waves traveling in various media, and discuss these light applications to modern technology.

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Agenda (lesson time)

During the Lesson (60 minutes):

How do we determine the frequency, wavelength and speed for a light wave?

What is light reflection?

What is light refraction?

Does light travel at different speeds in different mediums? Explain.

What does Snell’s Law tell us about how light waves bend or change direction?

How does light reflection and light refraction apply to modern technology?

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During the Lab (60 minutes):

Which lenses make the images appear larger, smaller or the same size?

How does a prism separate light into its constituent colors?

How does an image appear using a concave mirror? A convex mirror?

How does using two different mediums such as air and water distort the image of a straw in a glass of water or a drawing on a sheet of paper outside a glass of water?

Explain how all forms of electromagnetic radiation, not just visible light, can be reflected or refracted.

Intro/Driving Question/Opening

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• What other types of light waves besides visible light comprise the electromagnetic spectrum?
• Define “frequency,” “wavelength” and “speed” as they pertain to light waves?
• How might the speed of light change when it enters a different medium? For example, from air to water?
• Do light rays change their angles (bend) when they enter different mediums?
• Does light wavelength change in proportion with its light speed upon entering a new medium?
• Explain why mirrors reflect while lenses refract.
• Did you know that fiber optic cables and music CDs rely on light reflection?
• Did you know that optical lenses found in eyeglasses, telescopes and cameras rely on light refraction?
• What other technologies might rely on either light reflection, light refraction or both?

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Lesson Instructions

During Lesson:

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• Teacher reviews light waves, their speed, frequency and wavelength and explains how light waves can be transmitted through different materials and mediums.
• Teacher introduces the topics of light reflection and light refraction, provides examples of each, explains the differences between the two, and shares information on how they are currently used in modern technology.
• Teacher asks students driving questions about the topics listed above.
• Students complete an introductory lesson/assignment with multiple choice, matching, true-false and short answer questions and turn in their assignments for teacher review and grading.
• Teacher provides overview of Snell’s Law and uses guided instruction to help students complete word problems using this formula for teacher review and grading.

Hands-on Activity Lab Instructions

During Lab:

• Students working in teams of 2-4 students visit different lab stations already set up with light-related activities.
• Students take notes at each station on their “Team Lab Data Collection and Question Sheet” and answer questions.

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Lab Station Activities include:

• Analyzing images reflected in convex and concave mirrors
• Calculating angles of incident rays and reflected rays for both specular and diffuse reflection models
• Shining laser pointers on different magnification glass lenses to explore the refracted images on blank pieces of paper
• Shining flashlights through prisms to see white light dispersed into color spectrums reflecting the electromagnetic spectrum
• Observing angles of the incident ray and the refracted ray of straws in glasses of water
• Observing the distortion (refraction) of images held against a glass of water to visualize the apparent shift in the position of objects immersed in liquid mediums

Team Lab Data Collection and Question Sheet includes:

Data collected from students’ hands-on activities:

• Responses to questions on the relationships between frequency, wavelength, and the speed of light waves
• Knowledge of technologies using light reflection or light refraction, and suggested possible future applications

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Assessment

Students complete three (3) assessments while working together in groups of 2-4 students. These assessments are to be submitted for teacher review and grading:

Formative Assessment:

• Introductory lesson/assignment with multiple choice, matching, true-false and short answer questions

Summative Assessment:

• Snell’s Law Overview and Word Problems
• “Team Lab Data Collection and Question Sheet” which includes: 1) students’ analysis and interpretation of data they collected from their hands-on activities, 2) students’ responses explaining the relationships between frequency, wavelength, and speed of light waves traveling in various media, and 3) students’ knowledge of technologies using light reflection or light refraction, and suggested possible future applications

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Differentiation

Students who need further remediation during the lesson or lab component, specifically with their math calculations, will be given additional word problems to calculate the speed of light, frequency and wavelength of light waves using the formula: c = f x 𝛌, and/or they will be given additional Snell’s Law word problems to calculate the angles of incidence and refractions, and the indices of refraction for each medium using the formula:

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Remediation

Extension/Enrichment

For further enrichment, students may read articles explaining how light reflection or light refraction can be found in everyday natural phenomena such as rainbows, mirages, sunrises and sunsets.

Another enrichment activity entails students watching a documentary on rainbows, and how rainbows demonstrate both properties of light reflection and light refraction. Rainbows also reflect a specific angle of 42 degrees in the sky and are accompanied by a secondary rainbow (often faint and hard to see) at 50 degrees in the sky with the colors inverted. Students will complete a questionnaire after watching the documentary to assess their knowledge and comprehension.

A third enrichment activity is for students to keep a sunrise/sunset journal in which they record the time and duration of sunrises and sunsets over a specified period of time and compare this information to what is reported on weather forecasting websites and apps. Student first-hand data should indicate that daylight is extended in the morning and in the evening due to the refraction of sunlight. This is because sunlight is refracted in earth’s atmosphere and sunlight reaches us before our sun is actually physically above the horizon. Conversely, in the evening, sunlight is still visible after the sun has actually set.