Physics

CHAPTER 7 HOMEWORK

1. The surface of a lake will always reflect light.  It is less common for a lake to reflect a 

clear image of buildings and lights on the other side of the lake; this happens most often 

on still mornings or evenings.

a) What is the name for the type of reflection that the lake usually exhibits?  

b) What is the name for the type of reflection that the lake exhibitswhen it forms clear 

images?

c) What is the cause of the difference?  What conditions are necessary for the lake to 

act like a clear mirror?

2. The opening picture for the chapter shows an optical illusion which makes a pencil in a 

water glass appear broken.  Explain in your own words how the illusion is caused.

3. The book explains how a water mirage is formed from a hot surface. If you went to 

the moon, would you expect hot surfaces to create a mirage? Explain.

4. What optical effect causes nearsightedness?  Explain.  What kind of lens is used to 

correct nearsightedness, and why does this work?

5. If you hold a magnifying glass so that sunlight passes through it, a bright point of light 

will be formed in front of the lens.  This point is very hot in fact, magnifying glasses 

are included in survival kits to start fires.  

a) What shape of lens is used to create a magnifying glass is it thicker at the edges than 

in the middle, or vice-versa?

b) What is the proper name for the point where the light makes a bright spot?

c) Why is the bright spot so hot?  Explain.

6. A “bandshell” is a curved wall built outside where performances can be held for 

instance, this bandshell in Central Park, NY:

http://centralpark.org/index.php/attractions/bandshell/

What type of optical device does the bandshell act like? Music played in front of the 

bandshell is clear and audible for a surprising distance in front of the bandshell.  Why 

is this the case?  Explain using concepts from the chapter.

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7. You can hear a clear difference in the sound of a lecture in a carpeted room versus a 

room with a smooth, hard floor.  Why is this the case?  Use terms from the chapter to 

explain.  Which type of floor would be best to improve the clarity of the sound of the 

lecture?  Why?

8. If you were shopping and had two identical pairs of sunglasses, how could you tell if 

they were polarized inside the store?