Physics
Work Sheet
Sound : intensity & decibels
1. What is the decibel rating for a sound that has an intensity of
a. 8.75 x 10-5 W/m2 (dB= 79.4)
b. 4.28 x 10-8 W/m2 (dB = 46.3)
2. A sound source emits sound energy at 5.90J/s (5.90 watts).
a. Find the sound intensities at the following distances from the source:
i. 8.50 m (6.50 x 10-3 W/m2)
ii. 17.0 m (1.62 x 10-3 W/m2)
b. What is the ratio of sound intensity for i/ii ( 4/1)
c. Find the decibel readings for the sounds in part a.
i. ( 98.1)
ii. (92.1)
d. What is the ratio of decibel i to decibel ii? (1.06/1)
(note that a fourfold increase in sound intensity caused a 1.06 increase in the decibel rating
3. What are the characteristics of sound that make it a unique type of wave?
a. _______________________
b. _______________________
c. _______________________
d. _______________________
4. A firecracker produces a sound with an intensity of 1.58 x 10-3 W/m2.
a. What is the decibel rating of this firecracker?
b. What is the decibel rating of:
i. two of these firecrackers exploding at the same time? (2X intensity)
ii. three of these firecrackers exploding at the same time?
5. A jet plane emits 3.0 x 105J of sound energy per second.
a. What is the intensity of the sound 40 m away?
i. dB level at this position
b. Air absorbs sound energy at the rate of 7dB/km. Calculate the intensity of the sound
i. 1.0 km away
ii. 5.0 km away
iii. At what distance would the sound intensity reach 1x10-12W/m2?
6. A guitar has a string with a fundamental frequency of 196 Hz. Its length is 32 cm and its mass is 0.50g.
a. Under what tension must this string be tightened?
7. A sound wave reaches the outer ear with an intensity of 4.5 x 10-8 W/m2. How much energy will enter
the ear canal if the radius of the canal is 1.12 cm?