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Questions and Answers
What does the intensity of a sound wave primarily depend on?
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 acoustic impedance (Z) of a medium given by?
What is the hearing threshold intensity level in decibels (dB)?
What is the hearing threshold intensity level in decibels (dB)?
Which statement is true about the loudness of a sound?
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)?
What is the correct formula for calculating the intensity ratio in decibels (dB)?
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How is pitch of a sound determined?
How is pitch of a sound determined?
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At what intensity does sound reach the pain threshold?
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?
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?
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?
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.
