Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

# Homework Problems

Draw a ray diagram showing why a small light source (a candle, say) produces sharper shadows than a large one (e.g. a long fluorescent bulb).
A Global Positioning System (GPS) receiver is a device that lets you figure out where you are by exchanging radio signals with satellites. It works by measuring the round-trip time for the signals, which is related to the distance between you and the satellite. By finding the ranges to several different satellites in this way, it can pin down your location in three dimensions to within a few meters. How accurate does the measurement of the time delay have to be to determine your position to this accuracy?
Estimate the frequency of an electromagnetic wave whose wavelength is similar in size to an atom (about a nm). Referring back to book 4, in what part of the electromagnetic spectrum would such a wave lie (infrared, gamma-rays,...)?
The Stealth bomber is designed with flat, smooth surfaces. Why would this make it difficult to detect via radar?

The large figure shows a curved (parabolic) mirror, with three parallel light rays coming toward it. One ray is approaching along the mirror's center line. (a) Photocopy the diagram (or download the book and print out this page) and continue the light rays until they are about to undergo their second reflection. To determine the angles accurately, you'll want to draw in the normal at the point where the ray hits the mirror. What do you notice? (b) Make up an example of a practical use for this device. (c) How could you use this mirror with a small lightbulb to produce a parallel beam of light rays going off to the right?

The natives of planet Wumpus play pool using light rays on an elevensided table with mirrors for bumpers. Trace this shot accurately with a ruler to reveal the hidden message. To get good enough accuracy, you'll need to photocopy the page (or download the book and print the page) and draw in the normal at each place where the ray strikes a bumper.

Last Update: 2009-06-21