physics review Test 1 Flashcards
10^9 =
Gega (G), billion
10^6=
Mega (M), million
10^3=
Kilo (k), thousand
10^2 =
hecto (h), hundred
10^1 =
deca (da) , ten
10^-1
deci (d), tenth
10^-2
centi (c), hundreth
10^-3
milli (m) (thousandth)
10^-6
micro (u) millionth
10^-9
nano (n) billionth
What is the opposite of giga?
nano
What is the opposite of mega?
Micro
what is the opposite of kilo?
Milli
what is the opposite of hecto?
centi
what is the opposite of deca?
deci
How are sound pulses created in diagnostic ultrasound?
pulses travel through biologic tissue or media
what do all sound waves carry from one location to another?
energy
Name some different forms of waves :
heat
sound
magnetic
light
sound is a ____________ wave.
mechanical
Sound cannot travel through a ________, it must travel through a ________.
vacuum, medium.
When sound travels through a medium, the molecules are ___________ and _________.
compressed (squeezed together),
Rarefied ( stretched apart)
Sound travels in a ________ line.
straight
What type of waves are sound waves?
longitudinal
acoustic propagation properties
the effects of the medium upon the sound wave.
Biologic effects
the effects of the sound wave upon the biologic tissue through which it passes
What are the three acoustic variables?
Pressure, density, distance.
What is pressure? What unit is used for pressure?
concentration of force in an area
Unit: pascals (Pa)
What is density? What unit is used for density?
concentration of mass in a volume.
Units: kg/cm3
What is distance? What unit is used for distance?
measure of particle motion.
Unit: cm,feet, mile
What does the acoustic parameters of a sound wave tell you?
the waves features
Name the seven acoustic parameters that describe sound waves:
Period Frequency Amplitude Power Intensity wavelength Propagation speed
What direction do particles move in a transverse wave?
perpendicular to the direction that the wave propagates.
What direction do particles move in a longitudinal wave?
parallel to the direction the wave propagates.
When a pair of waves peaks occur at the same time and at the same location, what is is called?
in-phase
What happens when two waves are out of phase?
their peaks occur at different times.
When waves lose their characteristic and combine to form a single wave, what is this called?
interference
constructive interference
in phase waves formation of a wave with greater amplitude.
destructive interference
out of phase waves results formation of a single wave with lesser amplitude.
what can happen, when the frequencies of the waves differ?
both constructive and destructive interference occur.
What is the source of a sound wave?
the ultrasound system and the transducer
What is period? what units is used?
The time it takes a wave to vibrate a single cycle.
Units: time
ex: microseconds, seconds, hours, days.
What is frequency ? what units is used?
frequency is the number of particular events that occur in a specific duration of time.
Units: per second / hertz
In diagnostic ultrasound, what does the frequency range from?
2MHz to 15MHZ
Frequency of a soundwave less than 20Hz, and below the threshold of human hearing is called ?
Infrasonic or infrasound
Humans can hear sound frequencies between _______ and _________.
20 Hz and 20,000 Hz.
Sounds with frequencies so high that humans cannot hear it is called ?
Ultrasonic or ultrasound
Why is frequency important in diagnostic ultrasound?
It affects penetration and image quality.
How are period and frequency related?
they are inversely related.
Frequency is reported with units of Hz, some people believe that hertz means?
“cycles per second”
what is the meaning of a soundwave with a frequency of 100 hz?
100 cycles per second
What are the three parameters that describe the size, magnitude, or strength of a soundwave?
Amplitude, Power, Intensity
What does amplitude tell us in ultrasound?
The “bigness” of the a wave.
what is the equation for amplitude ?
A= Amax-Amin/2
What unit is amplitude measured in?
any of the acoustic variables
pressure- pascals
density- g/cm^3
particle motion- cm, inches
In ultrasound, what does pressure amplitude range from?
1 million pascals to 3 million pascals
What is the difference between amplitude and peak-to-peak amplitude ?
look at page 28 of physics book
what is power? what unit is used?
the rate of energy transfer or the rate at which work is performed. “bigness of wave”
unit: watts
In clinical imaging, typical powers range from
0.004 to 0.090 watts (4 to 90 milliwatts)
How are amplitude and power related?
power is proportional to the wave’s amplitude squared
A sonographer increases the amplitude of a wave by a a factor of 3. How has the power changed?
power is increased by a factor of 9
When a sonographer decreases the amplitude of a wave to 1/2 of its original value, how has the power changed?
decreased to 1/4
What is intensity?
Is the concentration of energy in a sound beam
How do you calculate intensity?
power (w)/ area (cm^2)
What are the units of intensity ?
Watts/square, centimeter, or w/cm^2
In clinical imaging, intensity ranges from _____ to ______.
0.01 to 300 W/cm^2.
How are intensity and power related?
directly related
How are intensity and amplitude related?
intensity is proportional to the wave’s amplitude squared
what is wavelength ?
it is the distance or length of one complete cycle.
For example, imagine a sound wave as similar to a train. Wavelength is the length of a single boxcar in a train.
what units is wavelength measured in ?
mm, meters, any unit of length.
Wavelength is the only parameter that is determined by the ___________ and ___________.
source and medium
In clinical imaging, wavelength in soft tissues ranges from _____ to _____.
0.1 to 0.8 mm
What is the relationship between wavelength and frequency?
inversely related
What is the wavelength of 1 MHz sound in soft tissue?
1.54mm
wavelength in soft tissue
- 54 mm
1. 54 mm/us
Why is wavelength important in diagnostic ultrasound?
Plays a major role in image quality.
shorter wavelengths are created by high frequency sound, producing high quality images with greater detail.
What is propagation speed?
rate at which a sound travels through a medium.
What units is speed measured in?
m/s, mm/us, any distance divided by time.
In the body, the speed of sound ranges from __________ to ____________.
500 m/s to 4000 m/s, depending on the tissue through which it is traveling.
Speed is only determined by ?
the medium.
The speed of sound in soft tissue?
1,540 m/s.
What is the equation of speed?
s= frequency (Hz) * wavelength (m)
What are the two characteristics of a medium that affect the speed of sound?
stiffness & density
What does stiffness describe in an object?
The ability of an object to resist compression.
What does density describe?
Density describes the relative weight of a material.
How are stiffness and speed related?
directly rated
How are density and speed related?
inversely related
A media with low density, will sound travel fast or slow?
fast
What does bulk modulus?
its the same as stiffness
Two terms that are opposite of stiff.
Elasticity and Compressibility
When stiffness increases, speed ________.
increases
When density increases, speed ________.
decreases
List the 5 parameters that are all initially determined by the sound source only
Period Frequency Amplitude Power Intensity
What parameters can the sonographer adjust ?
Amplitude, power, intensity
What parameter is the only one that is determined by both the sound source and the medium?
wavelength
Which parameter is the only that is determined by the medium?
speed
The effects of tissue on sound waves are called _______.
Acoustic propagation properties
The effects of a medium on an ultrasound wave are called?
Acoustic propagation properties.
Sound waves weaken, or _______ as they travel in the body.
Attenuate
What is the standard measurement for attenuation?
Db
Decibels are based on mathematical construct called what?
Logarithms
What is the log of 1,000 ?
3
What is the log of 10,000?
4
What are Db used for?
To report relative changes.
Give an example of relative change?
“the signal strength has doubled” or the signal is now one-tenth as large as it used to be.”
Decibel notation is :
A relative measurement
A comparison
A ratio
logarithmic
Positive decibels report signals that are _______ in strength, or getting _______.
increasing, larger.
When a wave’s intensity doubles, the relative change is what?
+3 Db.
When intensity increases ten-fold, the relative change is
+ 10 Db.
Negative decibels describe signals that are ________ in strength, or getting ______.
Decreasing, smaller.
When the intensity is reduced to 1/2 its original value, the relative change is ___.
-3db
When the intensity is reduced to 1/10 its original value , the relative change is _____.
-10 db
