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....

Discussion - Refraction and Images

Discussion Questions

A What index of refraction should a fish have in order to be invisible to other fish?
B Does a surgeon using an endoscope need a source of light inside the body cavity? If so, how could this be done without inserting a light bulb through the incision?
C A denser sample of a gas has a higher index of refraction than a less dense sample (i.e. a sample under lower pressure), but why would it not make sense for the index of refraction of a gas to be proportional to density?
D The earth's atmosphere gets thinner and thinner as you go higher in altitude. If a ray of light comes from a star that is below the zenith, what will happen to it as it comes into the earth's atmosphere? E. Does total internal reflection occur when light in a denser medium encounters a less dense medium, or the other way around? Or can it occur in either case?

Discussion Questions

(c) Two images of a rose created by the same lens and recorded with the same camera.

A In figures (a) and (b), the front and back surfaces are parallel to each other at the center of the lens. What will happen to a ray that enters near the center, but not necessarily along the axis of the lens?
B Suppose you wanted to change the setup in figure (a) so that the location of the actual flame in the figure would instead be occupied by an image of a flame. Where would you have to move the candle to achieve this? What about in (b)?
C There are three qualitatively different types of image formation that can occur with lenses, of which figures (a) and (b) exhaust only two. Figure out what the third possibility is. Which of the three possibilities can result in a magnification greater than one?
D Classify the examples shown in figure (c) according to the types of images delineated in the previous discussion question.
E n figures (a) and (b), the only rays drawn were those that happened to enter the lenses. Discuss this in relation to figure (c).
F In the right-hand side of figure (c), the image viewed through the lens is in focus, but the side of the rose that sticks out from behind the lens is not. Why?
G In general, the index of refraction depends on the color of the light. What effect would this have on images formed by lenses?

Last Update: 2009-06-21