1) Place a piece of paper on a table or flat surface. 2) Place your acrylic half-cylinder on the paper with one of its large, flat surfaces downward, and so that the narrow rectangular edge is at the midpoint of the paper. 3) Draw a line on the paper at the location of the narrow edge. 4) As carefully as you can, mark the midpoint of that edge. This should be the center of curvature of the arc, which I'll call C. 5) Now use your laser from a distance of a few inches away and aim it at C. Be sure to mark both the path of the incident laser beam as well as the point where it exits the acrylic on the curved face. 6) few times from different angles of incidence up to around 60 degrees. (Maybe 15, 30,45, 60). The angles need not be precise since we'll measure them precisely in a moment. 7) Take a picture to be included in your lab for one of the cases in part 6. 8) With the data of incidence angle and refracted angle, calculate for each case. 9) Indicate the four values you got as well as the average value. 10) Using this average value for , find the angle that should cause total internal reflection. (Show your work). 11) Once again using the laser, but with it incident on the curved side such that it strikes the acrylic at normal incidence, you have control of the angle the beam meets the flat, rectangular face (but from the inside of the acrylic). Take a picture of total internal reflection of this beam at (or just beyond) the angle you calculated, and include the picture in your lab.

Based on the last part (step 11), you should be able to make the beam undergo total internal reflection on the inside, flat, rectangular face of the acrylic half-cylinder by using any angle larger than the one you calculated. I want you to maintain such an angle that induces total internal reflection, and for you to frustrate it by placing your finger firmly on the spot where the laser meets the acrylic face. Pushing firmly will decrease the air layer to the extent that the light will pass through the air gap and end up on your finger. Keep in mind that it can't get to your finger otherwise, since it is reflected away. It should almost seem like a pressure-sensitive button. Push hard and light escapes to your finger. Press softly or not at all and it just reflects. This is a perfect analog, by the way, to barrier tunneling in quantum mechanics. Without changing the incidence angle for the laser, show that without your finger 100% of light intensity reflects, and that with your finger, light is transmitted through the acrylic-air interface, and therefore undergoes very little reflection. Take a picture of each condition and include them in your lab.