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In the simulation below clicking the FIRE button will emit a ray from the yellow source. Click and drag the yellow dot to change the position of the yellow source.. Click and drag the green dot to change the emission angle of the ray. The blue and yellow areas represent two different media.

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General Questions:

Ray diagrams are often used in geometric optics to describe the behavior of light in optical instruments. The rays in this simulation lack some of the characteristics of light. List some of the features of light that are not taken into account in this simulation.

Build It:

Design and build a device that uses components from your local hardware store to investigate the propagation of light across the boundary between two media.


1. Develop a systematic approach for using rays to investigate the behavior of rays as they interact with the interface between two different mediums. Identify the important physical variables involved.

2. Based on your initial experiments make a list of your observations.

3. Take quantitative measurements of the paths taken by the rays. ( You will need a protractor and a ruler to do this.)

4. Based on your data, find any mathematical relationships that exist between the important physical variables you identified in step 1. (Do not use any physics to do this; just use data analysis procedures.). Determine the value of all constants.


1. The search words listed below will provide URLs that discuss Snell's law. Use this law as a suggestion for how to use a transformation of variables so that you will expect your data to lie on a straight line whose slope is the ratio of the velocities of light in the two mediums.

2. Also use the URLs to find a discussion of the index of refraction and critical reflection. Use this information and your data to determine the ratio of velocities from the critical angle.

3. Do your results for the velocity ratio from step 1 agree with the ratio you found in step 2? What does the word "agree" mean in this context?

Keyword Search Results

1. Try the following search words at www.google.com. (Note: the quotation marks may, or may not, reduce the number of links listed by Google.)

"geometric optics" (240,000)

"index of refraction" tutorial (46500)

"Snell's Law" tutorial (21,300)

"data analysis" "physics lab" (49,600)

"transformation of variables" (401,000)

"curve fitting" "physics lab" (58,500)

"physics lab data analysis" {152,000)