10 Questions
What is the formula for the intensity of a sound wave at a reference intensity I0?
I0 = Imin / 10^12 (W/m²)
What is the effect of a large difference in acoustic impedance on sound waves?
High reflection and low transmission
What is the purpose of a stethoscope in medicine?
To amplify sounds made by the body
What is the pitch of a sound dependent on?
Its frequency
What is the hearing threshold represented by in an audiogram?
The faintest sounds that can be heard
What happens when the acoustic impedance of two media is equal (Z1 = Z2)?
There is total transmission and no reflection
What is the unit of sound intensity level?
dB (decibels)
What is the characteristic of sound that depends on its intensity?
Loudness
What happens when there is a sign change in the reflected wave?
There is a phase change
What is the purpose of an audiogram?
To diagnose hearing disorders
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.
Understanding the characteristics of sound waves, including reflection and transmission, intensity level ratio, and their applications in medicine, particularly in percussion and stethoscope use.
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