Hands-on Activity What’s Your Angle? Assessing Wave Refractions

Learning Objectives

After this activity, students should be able to:

• Explain that light refracts differently in different mediums.
• Accurately measure the angle of refraction in different mediums.
• Find the index of refraction using Snell’s law.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

State Standards

Materials List

Each group needs:

• 100-ml beakers (6 per group)
• 20 ml water
• 20 ml ethyl alcohol
• 20 ml clear dish soap
• 20 ml corn syrup
• 20 ml vegetable oil
• What’s Your Angle? Worksheet
• What’s Your Angle? Placemats (3 per group)
• one laser (prefer green laser)
• one protractor
• one ruler
• a dry-erase marker or masking tape (to label beakers)
• safety goggles (one pair per student)

Worksheets and Attachments

Pre-Req Knowledge

Student are expected to know:

• The basic properties of light, such as reflection, refraction, absorption, transmission and scattering.
• How to plot data points and determine the slope from the graph.
• How to use a protractor to measure angles.

Introduction/Motivation

(To get started, show students Figure 1 and ask them whether the pencil is really broken. Ask them to google the reason why the pencil looks broken. Ask them which behavior of the light phenomenon is demonstrated in this example. (Answer: Refraction) 

Then show one of these videos:

(2:35 minutes long): https://www.youtube.com/watch?v=lkv0uZTP_zo&t=82s

(4:52 minutes long): https://www.youtube.com/watch?v=zarxpu43-ls

(2:25 minutes long): https://www.youtube.com/watch?v=sv8-y7N0Ryw

(1:40 minutes long): https://www.youtube.com/watch?v=dPjvgYXJjzw)

When light passes from one medium to another, it changes speed. For example, when light passes from air to glass, it slows down. If light strikes a sheet of glass at a 90° angle, or perpendicular to the glass, it slows down but still passes straight through the glass. However, if light enters the glass at an angle other than 90°, the light bends as it slows down. The bending of light as it changes speed in a new medium is called refraction.

(Then show the students Figure 2.)

Figure 2 shows how refraction occurs. Notice that the speed of light changes again as it passes from the glass back to the air. In this case, the speed increases, and the ray of light resumes its initial direction. 

But do you know that light bends differently in different mediums?

If I experiment in two different beakers, where in one light travels from air to water and in another light travels from air to corn syrup, where do you think light will bend more: the corn syrup or the water? Let’s find out!

Procedure

Before the Activity

• Gather materials and make copies of What’s Your Angle? Worksheet, one per group. Place materials in a central area in the classroom.
• Make three copies of the What’s Your Angle? Placemats per group.

With the Students

1. Divide the class into groups of three or four students each.
2. Introduce the activity using the Introduction/Motivation section.
3. Give class instructions for the activity. Distribute copies of the What’s Your Angle? Worksheets and What’s Your Angle? Placemats.
4. Remind everyone to follow lab safety precautions since chemicals and glassware will be used.
5. Give each group lab materials. Have students mark the beakers with the liquid name and carefully place them on the placemats.

   

6. As students work through the What’s Your Angle? Worksheet, walk around and check on their progress. Ensure that students are working together and discussing their findings as a group. As appropriate, ask students the Investigating/Essential Questions to check on their understanding. The instructions on the worksheet are reproduced below for reference.

Instructions: Refraction Lab

Steps:

1. Take six 100-ml beakers.
2. Label the beakers with the medium name using masking tape or dry-erase markers as described below.

i)  Beaker 1 - air (leave the beaker empty)

ii)  Beaker 2 - water 

iii) Beaker 3 - ethyl alcohol

iv) Beaker 4 - clear dish soap

v) Beaker 5 - vegetable oil

vi) Beaker 6 - corn syrup

3. Add 20 ml of the labeled liquid to beakers 2 through 6.
4. Keep the six beakers in the circles on the placemats.
5. Search for the densities of the known liquids online.
6. Place the laser on the placemat. Note the laser should always stay flat on the table.
7. Turn on the laser and aim it toward beaker 1 at an angle.

   

    
8. Using a protractor, measure the angle the light from the beaker makes with the normal line (horizontal line).
9. On the opposite side, ask one member to measure the angle of the refracted light with the normal line.

   

10. Enter your data into the data table.
11. Repeat the procedure for the rest of the beakers, pointing the laser toward the liquid. Use the same angle of entry for each liquid.
12. Compute the index of refraction for each liquid using the angles from the data using the following formula:

    

13. Find the indices of refraction of the liquids used and enter them into the data table. Remember, because air is the first medium, the index of incidence (n1) will be 1.00.

Vocabulary/Definitions

electromagnetic wave: A wave that does not require a medium to travel; for example, it can travel through a vacuum. Also called an EM wave.

incident ray: A ray of light falling on the surface separating two mediums.

index of refraction: The value calculated from the ratio of the speed of light in a vacuum to that in a second medium of greater density.

medium: The material through which a wave travels. Gas (such as air), liquids (such as water), and solids (such as ropes) all act as mediums.

refracted ray: A ray of light traveling in another medium, with a change in direction.

refraction: The bending of waves as they enter a new medium at an angle, caused by a change in speed.

Snell’s law: A scientific equation that relates the index of refraction of a substance to the angle at which light bends in that substance. The mathematical form is n1sinθ1 = n2sinθ2, where n is the index of refraction (for substances 1 and 2) and θ is the angle at which light is refracted, as measured from a line perpendicular to the surface of the material (again for substances 1 and 2).

transverse wave: A wave that moves the medium at right angles to the direction in which the wave travels.

wave: A disturbance that carries energy from one place to another.

wavelength: The distance between one point on a wave and the exact same place on the next wave.

Assessment

Pre-Activity Assessment

Open-class discussion: Open the discussion by asking questions related to the wave phenomenon. Ask students to think about why a straw looks bent or broken in water and why objects viewed through a glass bottle appear distorted. Remind them that no idea is “silly.” All thoughts should be respectfully heard.

Activity Embedded (Formative) Assessment

Group Activity: Have students work in groups of three or four on the lab activity. Have them spread the What’s Your Angle? Placemats (three copies per group) on the desk and place the beakers on the spots. Each placemat has a spot for two beakers, and thus makes space for a total of six beakers. These placemats give a visual of where to place beakers but are optional to use.

Recording Data: Then students will take and record the data as per the instructions given in the What’s Your Angle? Worksheet.

Post-Activity (Summative) Assessment

Compare and Summarize: Students will utilize the What’s Your Angle? Worksheet to compare their data and observations. Then they will write the summary of the experiment as a conclusion.

Investigating Questions

Should a fisherman aim at the fish? In front of the fish? Or beyond the fish? Think carefully!!

Answer: We know that a light ray traveling from air to water will be refracted (change direction), and so will a light ray from water to air.

How should he adjust the angle of throw? (Answer: The fisherman should aim in front of the fish and throw the spear at a smaller angle.)

The refraction of light at the surface of water makes ponds and swimming pools appear to be a lot shallower than they really are.

Safety Issues

• Use safety goggles during this activity.
• Be extra careful while using lasers.
• Never stare directly into a laser, and never aim a laser beam at people.
• Write the following safety reminder on the board: Do not look directly into the laser.
• Wash hands with soap and water after the experiment.

Troubleshooting Tips

As needed, explain the Snell’s law formula and the diagram to students.

It may be necessary to briefly turn off the lights so students can see the path of the laser’s light through different mediums. 

Activity Extensions

A prism is a great example to demonstrate refraction application. When light passes from air to the glass of the prism, the change in speed causes the light to change direction and bend. Because of the differences in the refraction index between the air and the glass, light bends once it enters the prism.

Prisms are made in many different forms and shapes, depending on the application. Have students search for the type of prisms used in binoculars, monoculars, periscopes etc., and how each affects the movement of light.

Additional Multimedia Support

https://ingeniumcanada.org/scitech/education/try-this-out/broken-pencil-illusion

https://flexbooks.ck12.org/cbook/ck-12-middle-school-physical-science-flexbook-2.0/section/19.7/primary/lesson/refraction-ms-ps/

“What is Refraction of Light” video (2:35-min long): https://www.youtube.com/watch?v=lkv0uZTP_zo&t=82s.

Possible other videos:

https://www.youtube.com/watch?v=zarxpu43-ls

https://www.youtube.com/watch?v=sv8-y7N0Ryw

https://www.youtube.com/watch?v=dPjvgYXJjzw

References

Copyright

Contributors

Supporting Program

Acknowledgements

This curriculum was developed under National Science Foundation RET grant no. 1855147— Research Experience for Teachers in Advanced Design and Manufacturing at the University of Houston. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.