Optics Lab

Eliza Richardson, Pennsylvania State University-Main Campus
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Initial Publication Date: May 10, 2017 | Reviewed: May 10, 2019


In this activity, students will calculate the index of refraction of water by measuring the angles of incidence and refraction of light as it passes from air to water. They will follow directions to set up the experiment with cheaply available materials, make several measurements, then answer follow-up questions regarding the mathematical relationship between angles of incidence and refraction, experimental error and uncertainty.

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Learning Goals

Content/concepts goals
measure/calculate the angles of incidence and refraction of light as is passes from air to water. Find the relationship between the two.

Higher order thinking skills goals
Making measurements, assessing error and uncertainty, data analysis and visualization.

Other skills goals
Following directions, theory v. reality when making real measurements.

Context for Use

Type and level of course
This activity comes from a lesson in an online course that is part of a Master of Education in Earth Sciences program.

Skills and concepts students should have mastered
Students must have rudimentary knowledge of how to use a protractor, compass, and straightedge. Students must know how to create a table of measured values and construct a scatter plot from it.

How the activity is situated in the course
This activity could be used standalone as written. I use it as part of a larger lesson regarding the structure of Earth's interior and how body waves travel through the mantle. There are other activities in this same lesson that involve solving problems using Snell's law and how to construct a travel time curve with P waves.

Description and Teaching Materials

The full link to the activity:

Introductory blurb:
Often, optics is a topic covered in a physics class, not necessarily in an Earth science class. However, having a good grasp about how light waves are refracted and reflected at the interface between two materials will help us later when we have to visualize how seismic waves travel through the Earth. That's why we're going to have a little optics lab experiment here. The ultimate overriding objective in this lesson is for you to make your own observations using real seismic data and be able to picture in your head how seismic waves travel through the Earth's mantle. Before we jump straight into an activity that uses seismic data, let's back up and make sure we understand some principles of optics.
Optics Lab Activity Directions (Acrobat (PDF) 1.1MB May2 17)
Student Worksheet for the Optics Lab Activity (Microsoft Word 40kB May2 17)

Teaching Notes and Tips

This activity was created for an online class which means that the students are on their own wherever they are and need to find the right materials and follow the written directions. There's nothing dangerous or expensive here so you don't need to worry about that. The single biggest problem that will prevent students from "getting it" is not using a big enough container of water. If the tank is too small, the range of angles that are possible to measure in practice is too small to see the trend.


They turn in their problem set worksheet along with some photos of their experimental setup. I grade the problem set and critique their setup. At this point in human history I am assuming they all have a way to take a digital photo and attach it to a file, but you'll have to make allowances in case your students don't.

References and Resources

This is a link to the full activity in my course: