Physics 207
Homework Set #9
1) Briefly describe three methods for removing particulate mater from the exhaust of coal burning power plants. Indicate what size particles each method if effective at removing.
Gravitational Collectors: Flue gas passes through and “large” particles settle out, good for particles larger than 50
 m.
Cyclonic Collectors: Flue gas is forced into a mini tornado so that particles are thrown out: good for particles down to 5
 m.
Electrostatic precipitators: Large electric fields pull particles to the wall.
Good for particles down to 1
 m.
Fabric Filters: Works like a vacuum cleaner bag. Good for particles down to 0.1
 m.
2) How do we reduce sulfur dioxide emissions from coal burning power plants?
Sulfur dioxide is reduced by passing the flue gas through a water solution spray. The Sulfur dioxide reacts with calcium carbonate (Limestone) to form Calcium Sulfate and Caron dioxide.
3) The speed of sound is approximately 340 m/s. What is the wavelength of a pitch with a frequency of 440 Hz. What would be the wavelength of the WGLT primary frequency of 98.1 MHz. (Hint the speed of light is 3x10 8 m/s).

= c/f = (340m/s)/(440Hz) = 0.773m

= c/f = (3x10 8 m/s)/(98.1x10
6 Hz) = 3.058m
4) Why is the sky blue?
The sky appears blue because blue light is scattered more than red light.
Since when we look at the sky (not directly at the sun) we must be seeing scattered light, we see the sky as blue.
5) The temperature of the surface of the sun is approximately 6000K. What is the primary wavelength and frequency emitted by the sun. If the sun’s temperature were to increase by 10%, by what factor would its output power increase?
 max

2900
 mK / T

2900
 mK / 6000 K

0 .
483
 m

483 nm (visible light) f
 c /
 
( 3

10
8 m / s ) /( 483

10

9 m )

6 .
21

10
14
Hz
P f
 e

A ( 1 .
1 T
0
)
4 
( 1 .
1 )
4 e

AT
0
4 
( 1 .
1 )
4
P
0

1 .
464 P
0
The power output increases by 46.4% when the temperatu re increases by 10%.