1. Given a sound intensity of 6.0 x 10 -6 W/m 2 , find the intensity at the following distances from the source: a) The distance from the source doubles. b) The distance from the source quadruples. c) The distance from the source is halved. d) The distance from the source decreases to a third of the original distance
2. At close proximity (1.00m), rustling leaves have a sound intensity of about 1.2 x 10 -11 W/m 2 .
At what distance is the sound at the threshold of hearing (1.0 x 10 -12 W/m 2 )?
3. A sound source produces a sound power of 3.0 x 10 -3 W that arrives at a surface area
of 5.5 m 2 . Calculate the intensity of the sound at the surface.
4. If the sound intensity drops to 4.8 x 10 -5 W/m 2 in the previous question, a) what area does the sound intercept? b) what is the ratio of sound intensities? ( What is I
2
/I
1
? ) c) how much farther has the sound travelled? ( What is d
2
/d
1
? )
Complete questions 5 – 7 for practice with logs.
5. Find the logs of the following values: a) 100 b) 1000 c) 0.01 d) 3.5 x 10 -4 e) 5.67 x 10 6 f) 1 g) 0
6. Fid the inverse logs of the following : a) 2 b) 6 c) -2 d) -6 e) 3.5 f) 0.35
7. Knowing dB = 10 log (I
2
/I
1
), Calculate I
2
/I
1
if given the following dB values : a) 1 b) 4 c) -1 d) -3 e) 2.5 f) 0.5

8. The threshold of pain is 120 dB. Convert this to W/m 2 and then find out how many times more intense the threshold of pain is compared to the following dB values. a) normal conversation (60 dB) b) a whisper (20 dB) c) a rock concert (110 dB) d) 30 m from a freight train (75 dB)
9. At one point in the room, the sound intensity is 3.5x10
-6 W/m 2 . If you move twice the distance away, calculate a) the sound intensity in W/m 2 at this new distance. b) the difference in the decibels at these two location.
10. A hearing aid increases the sound intensity level, thereby allowing a person to hear better.
For the following decibel increases, by how much does the intensity of sound increase?
(solve by calculating I
2
/I
1
) a) 30 dB b) 22 dB c) 18.9 dB
11. A refrigerator lightbulb uses 25.0 W of power. A jack hammer produces a sound intensity of
110 dB. How many jack hammers would you need so that the sound power arriving at one square metre of surface could light one lightbulb, assuming 100% conversion of sound energy?
12. A rock concert produces sounds at 120 dB, measured 2.0 m away. How far back should you be in order to listen to the music at 100 dB?
13. A person has a threshold of hearing of 5 dB. Another person has a threshold of hearing of
25 dB. Which person has better hearing and by how much?
14. You and your friend have bought stereo systems. Your stereo has a signal-to-noise ratio of
50 dB, your friend’s stereo has a signal-to noise ratio of 60 dB. Who has the better system and by what factor? (calculate I
2
/I
1
for each stereo and compare these numbers)
15. If you could add the intensities of conversations between two people (65 dB), how many of them would you need to duplicate the sound intensity of a rock concert (120 dB)? (Hint, calculate I
2
/I
1
)
Answers
1.) a. 1.5 x10 -6 W/m 2 b. 3.8 x10 -7 W/m 2 c. 2.4 x10 -5 W/m 2 d. 5.4 x10 -5 W/m 2
2.) 3.46 m
3.) 5.45 x10 -4 W/m 2
4.) a)62.5 m 2 , b) 0.08867, c) 3.36X
5.) . a. 2 b. 3 c. -2 d. -3.5 e. 6.75 f. 0 g.
–
6.) , a. 100 b. 1000000 c. 0.01 d. 0.000001 e. 3.1 x10 3 f. 2.24
7.) a. 1.26 b. 2.51 c. 0.79 d. 0.50 e. 1.78 f. 1.12
8.) a. 10 6 b. 10 10 c. 10 d. 3.2 x10 4
9.) . a. 8.75 x10 -7 W/m 2 b. 6 dB
10.) , a. 1000 b. 158.5 c. 77.6
11.) 250
12.) 20 m
13.) 100
14.) 10
15.) 3.2 x10 5