PHYS 1112
Chapter 22 Problems

Chapter Objectives

1. Calculate the energy in a photon of light.
2. Describe and calculate the angle of reflection and refraction from light striking the interface between media.
3. Calculate the critical angle for total internal reflection.

Conceptual Questions

1. To determine the distance to a lightning strike, all one has to do is to begin counting when they see the flash and stop when they hear the thunder from the lightning. By dividing the number of seconds by 5, one has the number of miles to the lightning. Why does this work?
2. When looking down a black asphalt road on a hot summer day, it often looks like there is water far in the distance. Why does this mirage appear?
3. When looking at an aquarium from any angle other than perpendicular to any of the glass walls, the inside of the tank looks somewhat distorted (things are not where the appear to be nor do they appear to be the right size). Why?
4. If a laser beam is shot through a prism, does it cause a rainbow to form?

Selected Problems $$

1. Figure 22.5 shows an apparatus used to measure the speed distribution of gas molecules. It consists of two slotted rotating disks spearated by a distance s, with the slots displaced by the angle q. Suppose the speed of light is measured by sending a light beam toward the right disk of this apparatus. (a) Show that a light beam will be seen in the detector (that is, will make it through both slots) only if its speed is given by c = sw/q, where w is the angular speed of the disks and q is measured in radians. (b) What is the measured speed of light if the distance between the two slotted rotating disks is 2.5 m, the slot in the second disk is displaced 1/60 of one degree from the slot in the first disk, and the disks are rotating at 5555 rev/s?
2. A material with index of refraction n = 2.0 is in the shape of a quarter circle of radius R = 10 cm and is surrounded by a vacuum. A light ray, parallel to the base of the material, is incident from the left at a distance of L=5.0 cm above the base and emerges out of the material at an angle q. Determine the value of q.

Solutions