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 paperclip/pin 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 paperclips/pins. While keeping the paperclips/pins on the far side of the box lined up, stick two more paperclips/pins 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 paperclips/pins are in one line.

Exercise 3.1 (2 marks)

Submit a photograph of your experiment taken from above. The photograph should clearly show the location of your 4 paperclips/pins, your box, and the 45 degree line of sight you drew in Exercise 2. 

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

image

Note that because the edges of the box are parallel there are several angles that are the same and that the two lines above and below the box in the diagram are shifted due to refraction, but parallel to each other. By following this video, you should be able to measure the angle of incidence and the angle of refraction of light passing through your water-filled box:

 

Fill in the first row of the table below.

θinc

[deg]

θref

[deg]

sin θinc

[1]

sin θref

[1]

45

0.71

25

35

55

Chart Download

Now, repeat this experiment for incident angles of 25, 35 and 55 degrees. Keep in mind, you will have to re-draw your angle of incidence line at different angles each time. Also keep in mind that for an angle of incidence of 55 degrees you may need to move the box such your line of sight is still through the long edge of the box (see image below):

image

Exercise 3.2 (2 marks)

Complete and submit the above table.

Exercise 3.3 (4 marks)

i) Create a plot like the one you did in (1.2) of sin(θref) vs sin(θinc). Draw a line of best fit, and use it to calculate n1/n2.
ii) If we assume 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 the (fresh water) sea and you repeat the experiment by filling your box with air but it is surrounded by (fresh water). 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 fresh water in 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.