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Exercise 3: Measuring angles of refraction and index of refraction

In the last exercise, you observed light being ‘refracted’, causing the bottom half of your markers to appear shifted. Let’s try to quantify how much the light is refracted at the interface.

Continue filling your clear container with water until it is almost full, then look along the same line of sight you marked with your markers. While keeping the markers on the far side of the box lined up, stick two more markers on the side of the box closest to you such that they also line up with your perceived line of sight. From this perspective, it should appear that all of your markers are in one line.

Exercise 3.1 (2 marks)

Submit a picture of your experimental set-up taken from above. Your photo must clearly show the location of the student card(s) of the participating member(s) in this lab, along with your 4 markers, box, and the 45 degree line of sight you drew in Exercise 2.

Secondly, provide an additional image of the student card(s) used in the previous photo. Here, the student name(s) and student number(s) must be legible. With your experimental set up in the background, you may take this image from a closer view to ensure the student card(s) is/are in full focus. Note: you do not need to be in the photo. If you are completing this lab with others virtually, you may provide a screenshot of your video call, with the student cards of all members visible. Your experimental set up must still be visible in the background.

Remove your box (careful not to spill) and inspect the lines of sight marked by your markers. Draw lines alongside the markers as shown in the diagram below.

A schematic of the current set up, with a vertical line, a diagonal line with markers, and a rectangle that is labeled as the trace of the box. The angle between the vertical line and the diagonal line is labeled as the angle of incidence. A second diagonal line is found within the trace of the box, starting at the intersection between the vertical line and the top of the box. The angle between the second diagonal line and the vertical line is labeled as the angle of refraction. This angle is smaller than the angle of incidence. A third diagonal line is found on the bottom side of the rectangle, beginning where the second diagonal line intersects with the bottom of the rectangle. This third diagonal line is parallel to the first diagonal line.Note: Since the edges of the box are parallel, the diagonal lines above and below the box are also parallel to one another. However, these lines do not form a straight line as they are shifted due to refraction.

By further following the video from Exercise 2, you should be able to measure the angle of incidence and the angle of refraction of light passing through your water-filled box:

Note: If you would like to view this video in full screen, you can click on the McMaster logo found in the bottom right corner (this opens the video in a new tab).

Fill in the first row of the table below. This table can be found on the second tab of the Excel sheet provided in Exercise 1 of this lab.

A 5 by 4 table. The first row reads incident angle measured in degrees, refracted angle measured in degrees, sine of the incident angle, and sine of the refracted angle. The values for the incident angle are given as follows: 45, 25, 35, 55. The values for the refracted angle are left blank as an exercise. For the sine of the incident angle, only the first value is given, 0.71, while the rest of the column is left as an exercise. Finally, the entirety of the sine of the refracted angle is left blank as an exercise.Now, repeat this experiment for incident angles of 25, 35 and 55 degrees. Keep in mind, you will have to re-draw your line of incident angles for every new angle. You may find that for an angle of incidence of 55 degrees, you may need to move the box such that your line of sight is still through the long edge of the box (see image below):

A schematic of the previous set up, illustrating the possible horizontal translation of the box filled with water you may require. This is done to ensure your chosen objects may be seen through the long edge of the box, rather than a corner or through the width.

Exercise 3.2 (2 marks)

Complete and submit the above table.

Exercise 3.3 (4 marks)

i) Similarly to Exercise 1.2, create a plot of sin(θref) vs sin(θinc). Draw a line of best fit, and use it to calculate n1/n2.

ii) Based on your line of best fit, assuming that the refractive index of air is n = 1.00, what is the refractive index of water?

Exercise 3.4 (2 marks)

Now, imagine we live under water and you repeat the experiment by filling your box with air. If the angle of incidence is kept the same (45 degrees), what would the angle of refraction be in the box of air? Show your work. Assume the index of refraction of water is n = 1.33.

Before you continue!

Before continuing, be sure you have completed (3.1) to (3.4), which will be graded and submitted through Crowdmark.

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Physics 1A03 - Laboratory Experiments Copyright © by Physics 1A03 Team is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, except where otherwise noted.

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