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When the angles are small, you get a low-precision result. In the extreme case, measuring i = 0 ◦ and t = 0 ◦ tells you absolutely Lab 2c: The Speed of Light in Matter 43 Answers to Self-Checks for Chapter 2 Page 25, self-check A: He’s five times farther away than she is, so the light he sees is 1/25 the brightness. Page 31, self-check B: After the second reflection, the ray is going back parallel to the original incident ray. This is how the lunar ranging reflector in example 2 on page 22 worked, except in three dimensions rather than two.

Time-reversal symmetry Try sending the beam through a corner as suggested by the figure. Make sure that the incident angle of the incoming ray, marked with the dashed arc in the figure, is nice and big. 6 So far you’re just seeing things that you’ve already read about in the book. But now look inside the water. , passes into the water rather than bouncing back. We now have three rays: incident, reflected, and transmitted, which form the angles i, r, and t with respect to the normal. It’s easiest if you keep everything in a horizontal plane, because angles in three dimensions are hard to measure.

If you find that you can’t focus on both things at once, try making small adjustments to the distance between the lenses. The reason this problem can occur is that neither the focal lengths printed on the lenses nor the focal lengths you measured in part A are terribly accurate, so the distance between the lenses isn’t quite what it should be. The rays coming to your eye are therefore not quite parallel, which means that the image they form is not at infinity. Your body is not capable of simultaneously focusing one eye at infinity and one at a short distance.