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Questions and Answers
What is the formula for the intensity of a sound wave at a reference intensity I0?
What is the formula for the intensity of a sound wave at a reference intensity I0?
What is the effect of a large difference in acoustic impedance on sound waves?
What is the effect of a large difference in acoustic impedance on sound waves?
What is the purpose of a stethoscope in medicine?
What is the purpose of a stethoscope in medicine?
What is the pitch of a sound dependent on?
What is the pitch of a sound dependent on?
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What is the hearing threshold represented by in an audiogram?
What is the hearing threshold represented by in an audiogram?
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What happens when the acoustic impedance of two media is equal (Z1 = Z2)?
What happens when the acoustic impedance of two media is equal (Z1 = Z2)?
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What is the unit of sound intensity level?
What is the unit of sound intensity level?
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What is the characteristic of sound that depends on its intensity?
What is the characteristic of sound that depends on its intensity?
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What happens when there is a sign change in the reflected wave?
What happens when there is a sign change in the reflected wave?
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What is the purpose of an audiogram?
What is the purpose of an audiogram?
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Study Notes
Characteristics of Sound Waves
- A sound wave is a pattern of disturbance caused by energy traveling away from the source of the sound.
- Sound is a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium with a definite velocity.
- Sound travels fastest in solids, relatively slower in liquids, and slowest in gases.
Frequency and Wavelength of Sound Waves
- The number of rarefactions and compressions that occur per unit time is known as the frequency of a sound wave (f).
- The distance between successive compressions and rarefactions is known as the wavelength of a sound wave (λ).
- The speed of sound is given by: vs = fλ.
Sonic Spectrum
- The sonic spectrum can be classified into three frequency ranges: infrasound, audible sound, and ultrasound.
- The human ear can hear sounds in the range of roughly 20 Hz to 20 KHz.
- Infrasound refers to sound frequencies below the normal hearing range (<20 Hz).
- Ultrasound refers to sound frequencies above 20 KHz.
Infrasound
- Infrasound can travel long distances without losing much power due to its low absorption and large wavelength.
- Infrasound can produce clear symptoms including respiratory impairment and aural pain.
- Infrasound is used in the study of heart mechanical function.
Ultrasound
- Ultrasound is used clinically in various specialties.
- Ultrasound gives more information than an X-ray and is less hazardous for the fetus.
Intensity of a Sound Wave
- The intensity (I) of a sound wave is the energy carried by the wave per unit area and per unit time.
- Intensity is expressed by the maximum change in pressure (p0) as: I = p02 / 2Z.
Sound Intensity Level [Ratio]
- The absolute value of sound intensity (I) cannot be measured, but it can be compared to a reference intensity (I0).
- The intensity ratio is given by: 10 log (I/I0) = 10 log (10^12 W/m²).
Effect of Sound on Human Hearing
- Loudness (or volume) is the degree of sensation of sound produced in the ear, which depends on intensity.
- Pitch refers to whether a sound is high (sharp) or low.
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: Iref/Iin = (Z2 - Z1) / (Z2 + Z1).
Applications of Audible Sound in Medicine
- Stethoscopes are diagnostic instruments that amplify sounds made by the body from the heart, lungs, or other body sites.
- Modern stethoscopes consist of a bell with a thin diaphragm, tubing, and earpieces.
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Description
Understanding the characteristics of sound waves, including reflection and transmission, intensity level ratio, and their applications in medicine, particularly in percussion and stethoscope use.
