Sound Waves: Characteristics and Applications · Lesson 7 of 14
Amplitude and Intensity of the Sound Waves
“Amplitude measures the size of density variation, while intensity measures the sound energy crossing unit area per unit time.”
• Define amplitude for the density representation of sound. • Relate larger amplitude to greater energy. • Define intensity of sound. • Explain why intensity decreases with distance. • Distinguish amplitude from intensity.
Two sound waves can have the same spacing between compressions yet differ greatly in strength. One can produce only a small density change while another produces a much larger change. Amplitude describes this size of variation.
Amplitude and Intensity of the Sound Waves
The maximum change in the density of air in a compression or rarefaction compared with the average density.
A larger amplitude means the compression reaches a density farther above average and the rarefaction can fall farther below average. In the grain-on-membrane activity, striking a sound source harder transfers more energy, causing larger vibration and greater grain movement.
The amount of sound energy passing through a unit area perpendicular to the direction of propagation in unit time.
Amplitude and energy are related: a wave with greater amplitude carries more energy than a wave with smaller amplitude. Intensity, however, is defined in terms of energy passing through area per unit time.
Why Intensity Falls With Distance
As sound spreads away from a source, its energy is distributed over a larger region. The same energy is therefore spread over more area, so the intensity becomes smaller with increasing distance.
Amplitude describes the size of the oscillation in the wave representation. Intensity describes the rate of sound-energy flow through area. They are related but they are not the same definition.
Quiz
Which description best matches Amplitude?
Which description best matches Intensity of Sound?
Which term matches this description: The maximum change in the density of air in a compression or rarefaction compared with the average density.
Which term matches this description: The amount of sound energy passing through a unit area perpendicular to the direction of propagation in unit time.
Which statement is a key takeaway from this lesson?
Practice Problems
- Define amplitude using density rather than vertical displacement.
- Why does striking a plate harder make grains jump higher in the membrane activity?
- State the definition of intensity.
- Explain why sound intensity decreases as a wave spreads away from a source.
Key Takeaways
• Amplitude describes the maximum disturbance produced in the medium from its mean state. • Greater amplitude generally corresponds to a stronger sound wave. • Intensity measures the sound energy passing through unit area per unit time. • Amplitude and intensity are related but they are not the same physical quantity.