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Questions and Answers
What does the intensity of a sound wave primarily depend on?
What is the acoustic impedance (Z) of a medium given by?
What is the hearing threshold intensity level in decibels (dB)?
Which statement is true about the loudness of a sound?
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What is the correct formula for calculating the intensity ratio in decibels (dB)?
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How is pitch of a sound determined?
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At what intensity does sound reach the pain threshold?
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What is the intensity level (in dB) of a whisper with an intensity of $1 x 10^{-10}$ W/m²?
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What happens to the reflection ratio when there is a large difference in acoustic impedance between two media?
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Which source of sound has an intensity level of 75 dB?
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Study Notes
Intensity of Sound Waves
- Intensity (I) of a sound wave is the energy carried by the wave per unit area, and per unit time, measured in units W/m².
- Intensity can be expressed by the maximum change in pressure (p₀) as: I = p₀² / 2Z, where Z is the acoustic impedance of the medium.
- Acoustic impedance (Z) = ρvς.
Sound Intensity Level
- Sound intensity level is a ratio of intensity (I) to a reference intensity (I₀), where I₀ = 10⁻¹² W/m².
- Intensity ratio is measured in decibels (dB) as: 10 log (I / I₀).
- Hearing threshold intensity level is 0 dB, corresponding to 10⁻¹² W/m².
- Pain threshold intensity level is 120 dB, corresponding to 1 W/m².
Sound Sources and Intensities
- Examples of sound sources with corresponding intensity levels and intensities include:
- Jet plane at 30 m: 140 dB, 100 W/m²
- Threshold of pain: 120 dB, 1 W/m²
- Loud rock concert: 120 dB, 1 W/m²
- Siren at 30 m: 100 dB, 1 x 10⁻² W/m²
- Auto interior, at 90 km/h: 75 dB, 3 x 10⁻⁵ W/m²
- Busy street traffic: 70 dB, 1 x 10⁻⁵ W/m²
- Talk, at 50 cm: 65 dB, 3 x 10⁻⁶ W/m²
- Quiet radio: 40 dB, 1 x 10⁻⁸ W/m²
- Whisper: 20 dB, 1 x 10⁻¹⁰ W/m²
- Rustle of leaves: 10 dB, 1 x 10⁻¹¹ W/m²
- Threshold of hearing: 0 dB, 1 x 10⁻¹² W/m²
Characteristics of Sound
- The human ear can distinguish two characteristics of sound: loudness and pitch.
- Loudness depends on intensity.
- Pitch depends on frequency.
Sound Reflection and Transmission
- When a sound wave is applied perpendicularly to the interface between two media with different acoustic impedance, a portion of the wave will pass through and another will reflect.
- The ratio of reflected to incident waves can be measured as R = Iref / Iin.
- The reflection ratio is high when there is a large difference in acoustic impedance between the two media.
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Description
This quiz covers the concept of sound intensity, its unit of measurement, and how it is expressed in terms of maximum change in pressure and acoustic impedance.
