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Physics Module 1
Vocabulary
| Term | Definition |
|---|---|
| sound | the transmission of mechanical vibrations through a medium |
| wave | a mechanism which transfers energy, not matter |
| compression | region of highest acoustic variables (pressure, density, temp, & particle motion) |
| rarefaction | region of lowest acoustic variables (pressure, density, temp, & particle motion) |
| mechanical waves | need a medium to propagate (sound is an example) |
| electromagnetic waves | able to propagate in either a medium or a vacuum (light, heat, gamma rays, TV signals are all examples) |
| transverse waves | particle motion that is PERPENDICULAR to the wave propagation direction |
| longitudinal waves | particle motion that is PARALLEL to the wave propagation direction; moves along/in the same direction |
| acoustic variables | mechanical changes in the medium that are measured in 4 physical quantities |
| pressure (P) | force/unit area |
| acoustic pressure | the force of compression applied to a unit area of the medium by the sound wave |
| density (p) | mass per unit volume |
| temperature | the degree or intensity of heat present in a substance or object |
| particle motion | particles vibrate back & forth in their original position & do not travel with the wave |
| frequency (f) | a measure of how many times an event occurs in time |
| infrasound | below human's ability to hear (0 Hz - 20 Hz) |
| audible sound | 20 Hz - 20 KHz |
| ultrasound | above human's ability to hear (>20 KHz) |
| diagnostic ultrasound | 2 MHz - 12 MHz |
| period (T) | time needed to complete one cycle |
| wavelength | the physical distance one cycle occupies |
| propagation velocity (c) | the distance sound can travel per unit of time |
| amplitude (A) | the maximum variation of an acoustic variable from its mean value; a measure of how big or how strong |
| power (W) | the rate at which energy is transferred |
| intensity (I) | the concentration of power per unit area |
| elasticity | the ability of an object to return to its original shape after being mechanically deformed by an external force |
| compressibility | a measure of how much the volume of an object changes when pressure is applied to it |
| density | mass/unit volume |
| stiffness | the inverse of compressibility |
| bulk modulus | similar to stiffness |
| decibels (dB) | units used to measure the intensity of a sound by comparing it with a given level on a logarithmic scale |
| reflection | a change in direction of the propagating acoustic energy as it strikes the boundary between two mediums & returns to the source |
| specular reflection | occurs when an ultrasound wave is incident on to a large, smooth surface |
| diffuse reflection | occurs when the ultrasound wave is incident on to a rough, irregular surface |
| Rayleigh scattering | occurs when the reflecting structures are much smaller than the wavelength of the incident ultrasound wave |
| acoustic impedance | the resistance to ultrasound travelling through a medium |
| angle of incidence | formed between the direction of the ultrasound wave (beam direction) & the line perpendicular to the interface |
| normal incidence | occurs when the ultrasound beam is orthogonal (perpendicular) to the interface |
| oblique incidence | occurs when the ultrasound beam is not orthogonal to the interface |
| refraction | occurs when an incident ultrasound beam changes direction or bends on the transmission side of the interface |
| angle of transmission | the angle made by the direction of the transmitted ultrasound wave (beam direction) and the perpendicular to the interface (normal line) |
| Snell's law | the ratio of propagation speeds for two mediums in contrast is proportional to the ratio of the Sines of two angles: the angle of incidence & the angle of transission |
| degree of refraction | the absolute difference between the incident and transmitted angles |
| critical angle | incident angle at which total internal reflection occurs |
| attenuation | the reduction in intensity & amplitude of an ultrasound wave as it travels through a medium |
| attenuation coefficient | the amount of attenuation per cm (unit dB/cm) per MHz of frequency |
| half intensity depth | depth at which the intensity is reduced to 1/2 of its original value |
| simple harmonic motion | the vibration of a source to create motion |
| meter | the distance light travels in a vacuum |
| acoustic intensity | acoustic power per unit area of the sound beam |
| transmission | portion of the energy transmitted through an interface |
Created by:
ginaliane
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