Inverse Square Law (of Sound Waves)
Probeware
/ Instrumentation
SED 695B; Fall 2005
SED 695B; Fall 2005
Research Question:
How loud is your music?
or
How does sound level change with distance?
Standards addressed:
Physics:
Waves
4. Waves have characteristic properties that do not depend on the type of wave. As a basis for understanding this concept:
a.
Students know waves carry energy from one place to another. d.
Students know sound is a longitudinal wave whose speed depends on the properties of the medium in which it propagates. f.
Students know how to identify the characteristic properties of waves: interference (beats), diffraction, refraction, Doppler effect, and polarization.
Independent variable
Dependent variables
Controls
Series
distance
Sound Level
Materials
Procedures
- Computer with Wave Generator
- Two speakers.
- Sound Intensity Meter (probeware).
- Set up a speaker with a given tone, with a set volume.
- Measure the sound level at increasing distances from the speaker.
- Graph and analyze your data.
| Distance from Speaker (cm) | Sound Level (dBC) |
|---|---|
0 |
|
5 |
|
10 |
|
15 |
|
20 |
|
25 |
|
30 |
| Distance from Speaker (cm) | Sound Level (dBC) |
|---|---|
0 |
107.32 |
5 |
98.58 |
10 |
93.13 |
15 |
91.96 |
20 |
91.05 |
25 |
90.65 |
Why can you hear your headphones, but others cannot?
The farther away you are, the less intense the sound! That is if you double your distance, the intensity of sound decreases by 4 times. If you triple your distance, sound intensity decreases by 9 times!
References & Links:
Information on sound and the Inverse Square Law
Websites on interference
- Hyperphysics
- From Joseph Alward, University of the Pacific (with applets and practical applications)
- A simple animation showing constructive and destructive interference.
- The Physics Classroom: A more comprehensive look, with animations and in-depth explanations.
- Animation showing how standing waves are created as a result of constructive and destructive interference.