Physics Flashcards
Describe sound waves.
mechanical, longitudinal wave made by vibrating material, carried through the medium, transferring the Energy
Sound needs a medium, no sound in a vacuum/space
Describe the anatomy of the ear.
Outer ear: funnel (collect sound)
Middle ear: MIS Malleus, Incus, Stapes (hammer, anvil, stirrip) (levers that increase the size of vibrations; amplify sound)
Inner ear: convert vibrations to electrical signal for the brain
Describe how the sound travels from outer ear to inner ear.
Sound waves vibrate the ear drum (lightly stretched membrane in middle ear)
Vibration of ear drum vibrates hammer-anvil-stirrup
Oval window vibrations create waves in liquid in cochlea
Movement of liquid causes tiny hair cells to bend
Bending of hair cells stimulates nerves, sends electrical signals to brain
The speed of sound depends on the
- medium
- temperature
It’s fastest in warm solids and slowest in cool air.
Define Pitch.
how high or low a sound seems
Define Frequency.
number of wave cycles per second
Define Doppler Effect.
apparent change in frequency of sound caused by motion of observer or source.
Sound waves are moving forward/same direction of the train: Constructive interference makes it sound louder.
Define Loudness and its unit.
how well a sound can be heard
decibel - (loudness unit) 0 dB: softest humans can hear 120 dB: hurts
Define Sound Quality.
the result of the blending of several pitches through interference
Define sound.
A Consequence of mechanical energy.
Energy is applied to a medium.
Oscillations of molecules are produced.
When molecules move back and forth, they affect the other molecules directly next to them, producing alternating compressions and rarefactions.
Sound travels faster through?
Sound travels faster through Denser mediums.
The molecules are closer together and therefore they are more affected by their neighboring molecules
Define penetration in terms of sonography.
The depth of the tissue that an echo can be received back from.
Higher frequency probes (5 to 20 MHz), provide better resolution but have limited depth of view, used for superficial structures and children.
Lower frequency probes (2 to 5MHz), are lower resolution and can be used to image deeper structures.
Define resolution.
The ability to discriminate two points from each other.
Increasing the number of compressions and rarefactions for a given distance can more accurately discriminate between two separate structures.
Define frequency.
Frequency is cycle per second
As frequency increases, the wavelength decreases,and penetration into tissues decreases.
High frequency results in improved resolution
Define a transducer.
converts one form of energy to another
Rows of elements (crystals) are excited by electrical voltage.
The element contracts and expands (electrical energy is converted to mechanical).
This ability is the Piezoelectric effect.
The property (size and thickness) of the element together with the voltage, determine the frequency at which it vibrates or pulses
The transducer is also the receiver
Sonography machine modalities.
B-Mode: Brightness mode
M- Mode: motion mode
Color Doppler: displays direction and presence of blood flow
Spectral Doppler: displays absolute velocity of blood flow
Power flow: determines presence of blood flow.
The doppler effect in sonography.
A measurement of the difference in frequency between what is transmitted and what is received. A velocity (speed) of the object can be calculated.
If a higher frequency is returned = object is coming toward the source.
Tells velocity and direction of a moving object
Define mechanical wave.
a disturbance in matter that transfers energy through the matter.
Sound is a __ wave.
mechanical longitudinal compressional wave.
Does sound require a medium for the travel of the wave?
Yes.
Sound wave particles move __ of the wave.
parallel to the direction of the wave.
Areas of the wave with high pressure/density are called?
Compressions
Areas with low pressure/density are called?
Rarefactions.
Define frequency.
Number of cycles per second.
One cycle is 1 complete compression and rarefaction.
Define Hertz.
Cycles per second.
ex. 2 cycles per sec = 2Hz
What is magnitude?
Distance away from baseline of the wave.
What’s the frequency range for audible sound?
20-20k Hz
Define infrasound.
sound below 20Hz
we can’t hear it
Define ultrasound.
sound above 20k Hz
we can’t hear it.
__ frequencies popagate further without weakening.
Lower
Define diagnostic ultrasound.
2 megaHz - 20 megaHz
mega means 10^6 (millions)
What are the acoustic variables (changes in sound)?
pressure f/a
density m/v
temperature (as pressure changes, the temp changes)
particle motion (a distance measurement basically)
Define attenuation.
the weakening of sound waves.
__ frequencies attenuate faster.
Higher frequencies
Define wavelength.
the length 1 wave cycle takes up (compression and rarefaction)
velocity/frequency = wavelength
What’s the formula for wavelength?
v/f
and
c/f
c is the propagation speed with is the same thing as velocity.
define reflection.
sound waves bouncing back from a medium.
Define refraction.
change in direction of sound as it crosses a boundary.
What must be present for refraction to occur?
it must hit in an oblique angle
and the propagation speed of the mediums have to be different
Define constructive interference.
when two waves combine to make a wave greater than both of them.
Define destructive interferecne.
when the two waves do compressions at different times, the two waves combine to make a wave less than both of them.
If the two waves are perfectly synchronized, what happens?
the waves cancel each other out.
define intensity of a wave.
power/area
changing the amplitude of a wave, changes its energy and therefore its intenisty.
Define pitch.
frequency of the wave (aka Hz)
define loudness.
the intensity of the sound
measured in decibels.
