Simple Nature - Light and Matter

64 Zahra likes to play practical jokes on the friends she goes

hiking with. One night, by a blazing camp fire, she stealthily uses

a lens of focal lengthfto gather light from the fire and make a hot

spot on Becky’s neck. (a) Using the method of section 12.3.2, p. 792,

draw a ray diagram and set up the equation for the image location,

inferring the correct plus and minus signs from the diagram. (b)

LetAbe the distance from the lens to the campfire, and Bthe

distance from the lens to Becky’s neck. Consider the following nine

possibilities:

B

< f =f > f

A

< f

=f

> f

By reasoning about your equation from part a, determine which of

these are possible and which are not. .Solution, p. 1051

Key to symbols:

√easy typical challenging difficult very difficult

An answer check is available at http://www.lightandmatter.com.

844 Chapter 12 Optics