Ultrasound Physics: Chapter3 Describing Sound Waves Q&A
A top is spinning on a table. What is the period of the spinning top
0.05seconds (Units of time)
What is the range of periods commonly found in waves produced by ultrasound systems
0.06 to 0.5us
If the power in a beam is 1 watt and the area is 5cm2, what is the beam's intensity
0.2W/cm2. Intensity has units of W/cm2. We must find out how many watts there are and divide them by the number of cm2. The question states that there is 1watt. The area is 5cm2. Thus the intensity is 1/5 or 0.2W/cm2
What is the wavelength of 3 MHz sound in soft tissue
0.51mm. In soft tissue wavelength equals 1.54mm divided by the frequency in MHz. Thus, 3MHz sound will have a wavelength of 0.51mm
What is the wavelength of a wave with a unknown frequency traveling in soft tissue A. 0.51us B. 0.51m/s C. 0.51watts E. 0.51mm
0.51mm. Is the only answer with units of distance. A has units of time B has units of speed, C has units of pressure and D has units of power
What is the wavelength of 2MHz sound in soft tissue
0.77mm. South tissue, wavelength equals 1.54mm divided by the frequency in MHz. Thus 2MHz sound will have a wavelength of 0.77mm
Which of the following are acceptable units for the amplitude of an acoustic wave
1) cm 2) pascals
Which of the following are considered acoustic variables (More than one answer
1) density 2) particle motion 3) pressure
Which of the following are considered acoustic parameters
1) frequency 2)period
Which of the following units are appropriate to describe the period of an acoustic wave?
1) minutes 2) microseconds
The intensity of an ultrasound beam is defined as the___ in a beam___ by the ___ of the beam
1) power 2) multiplied 3)diameter
Using a particular ultrasound system and transducer, which of the following cannot be changed by the operator
1) wavelength 2)frequency 3)propagation speed 4)period
What determines the intensity of an ultrasound beam after it has traveled through the body
1)The sound wave's source 2) The medium though which the sound travels
Using a particular ultrasound system and transducer which of the following can be changed by the operator
1)intensity 2)power 3)amplitude (amp)
A sound beam travels a total of 10cm in 2seconds. What is the speed of the sound
10cm/2sec=5cm/sec
Of the four whose frequencies are listed below, which has the shortest period A. 12kHz B. 6,000Hz C. 205Hz D. 1kHz
12kHz
What is the period of the east's rotation
1Year
What is the range of frequencies emitted by transducers used in ultrasonic imaging
2,000,000 to 15,000,000 Frequencies
The maximum value of the density of an acoustic wave is 60lb/in2 while the minimum density is 20lb/in2. What is the amplitude of the wave
20 lb/in2. To calculate the amplitude of a wave subtract the minimum value of the acoustic variable from its maximum and then divide the number in half. 60-20=40lb/in2 and half of 40 is 20lb/in2
Which of the following waves is infrasonic
2Hz
The amplitude of an acoustic wave decreases from 27 pascals to 9 pascals. If the initial power in the wave was 27 watts what is the wave's final power A. 3watts B. 9watts C. 1watts D. none of the above
3watts. Alterations in a wave's power are proportional to changes in its amplitude squared. The power is reduced to one-third of its previous value( from 27 to 9 pascals). One -third squared equals one-ninth of the wave's original power remains. The initial power in the wave was 27 watts, one-ninth of that is 27/9, or 3watts.
Identify the wave that is ultrasonic
4MHz
Which of these waves is ultrasonic and most useful in diagnostic sonography A. 400MHz B. 4Mhz C. 2kHz D. 200,000Hz
4MHz
Identify all the waves that are inaudible (more than 1 answer may be correct) A. 4MHz B. 400kHz C. 28Hz D. 2Hz
4MHz, 400kHz, 2Hz. These are waves and inaudible and cannot be heard by humans
The frequency of a continuous acoustic wave is 5 MHz. The wave is then pulsed with a duty factor of 0.1. What is the new frequency
5MHz. Frequency is the reciprocal of the period. The fact that a wave is pulsed rather than continuous does not alter the frequency of the signal. The new and old frequencies are the same 5 million second
Which of the following waves has the longest period A. 2MHz B. 4,000Hz C. 6Hz D. 1kHz
6Hz
Of the four waves whose periods are listed below, which has the highest frequency A. 8s B. 80us C. 8Ms D. 800ks
80us
Of the four waves whose period are listed below, which has the lowest frequency A. 8s B. 80us C. 8Ms D. 800ks
8Ms
The effects of tissue on sound waves are called
Acoustic propagation properties
The effects of sound waves on tissue in the body are called
Bioeffects
Does the medium or the sound source determine parameters for wavelength
Both medium and sound source
Which of the follow cannot be considered a unit of frequency
Cycles
T/F If the amplitude of a wave is increased to 3 times its original value, the intensity is increased by 6times
False
T/F Propagation speed increase as frequency decrease
False
T/F Propagation speed increases as frequency increases
False
T/F The sonographer has the ability to alter the period of an ultrasound wave that is produced by a basic transducer
False
T/F With standard ultrasound pulses, the frequency of the ultrasound changes significantly as the wave propagates through the body
False
When the power in an acoustic beam is doubled and the cross sectional area of the beam is halved, then the intensity of the beam is
Four times larger
What is the reciprocal of period
Frequency
What term describes the number of cycles that an acoustic variable completes in a second
Frequency
The amplitude of an acoustic wave is increased. Which of the following will most likely remain unchanged?
Frequency and period
Ultrasound is defined as a sound with a frequency of
Greater than 0.02Mhz
What is characteristic of acoustic waves with frequencies exceeding 20,000 Hz when compared with waves have frequencies of less than 20,000Hz
Humans can't hear them
What happens to the intensity of an ultrasound beam when the beam's cross sectional area remains unchanged while the amplitude of the wave triples
Increases ninefold. A change in the intensity of a wave is proportional to the change in the amplitude of the wave squared. When the amplitude of a wave it tripled the intensity is increased ninfold (3times3=9)
A sonographer adjusts the output power of the wave emitted by the transducer. Which of the follow also changes?
Intensity
What happens to an acoustic beam's intensity when the power in the beam increases by 25% while the cross sectional area of the beam remains the same
It increases by 25%. The intensity is equal to the power divided by the beam area. If the power increases by 25% while the beam's area is unchanged then the intensity is also increased by 25%
Does the medium or the sound source determine parameters for propagation speed
Just medium
Does the medium or the sound source determine parameters for amplitude (amp)
Just sound source
Does the medium or the sound source determine parameters for frequency
Just sound source
Does the medium or the sound source determine parameters for intensity (In)
Just sound source
Does the medium or the sound source determine parameters for period
Just sound source
Does the medium or the sound source determine parameters for power (P)
Just sound source
Infrasound is defined as a sound with a frequency of
Less than 20Hz
The final amplitude of an acoustic wave is reduced to one-half of its original value. The final power is___ the original power A. The same as B. one-half C. double D. noe of the above
None of the above. Changes in the power of a wave are proportional to changes in the wave's amplitude squared. One half squared equals one quarter (1/2 * 1/2= 1/4). When one-half of the wave's original amplitude remains, then only one -fourth of the original power remains.
With standard ultrasonic imaging, what happens to the period of a wave as it propagates
Remains the same
The wavelength of an ultrasonic wave is determined by
The sound source and the medium through which the wave travels
What determines the initial intensity of an ultrasound beam
The sources of the acoustic wave
What determines the initial amplitude of an ultrasound wave
The transducer
What determines the period of an ultrasound wave
The transducer
What establishes the frequency of an ultrasound wave
The transducer
If the power of the beam is tripled while the cross sectional area of the beam remains the same it intensity
Triples
T/F A sonographer can routinely change the power of a wave emitted by a transducer used in diagnostic ultrasonic imaging
True
T/F A wave with a frequency of 15,000 MHz is ultrasonic
True
T/F If the periods of two waves are the same, then the frequencies of the waves must also be the same
True
T/F The period of an ultrasound wave is related to the frequency and is the same regardless of whether the wave is pulsed or continuous
True
T/F Waves in the ultrasound range behave in the same general manner as sound waves that are audible
True
T/F What standard diagnostic imaging instrumentation the sonographer has the ability to vary the amplitude of a sound wave produced by the transducer
True
T/F With diagnostic ultrasonic imaging instruments, the operator can alter the intensity of an ultrasound beam produced by a transducer
True
T/f Propagation speed does not change as frequency increase
True
The wavelength of a cycle in an ultrasound wave can be reported with which units
Units of distance
What are the units of the transmitted intensity of a sound wave
W/cm2
What are the units of power
Watts
What are the units of intensity
Watts/cm2
As an ultrasound wave travels through the body its amplitude usually
decreases
As sound travels in the body what typically happens to the intensity of the wave
decreases
Typically, as an ultrasound wave travels through soft tissue, the power of the wave
decreases
Amplitude and intensity
directly related
Amplitude and power
directly related
Power and intensity
directly related
Stiffness and sound speed
directly related
If intensity remains the same while the power is doubled, what has happened to the beam area
doubled
What are the units of frequency
hertz
Which of the following characteristics will create the slowest speed of sound
high density, low stiffness
What is characteristic of acoustic waves with frequencies of less than 20Hz when compared with waves having frequencies of more than 20Hz
humans can't hear them
Acoustic velocity and compressibility
inversely related
Acoustic velocity and density
inversely related
Elasticity and speed of sound
inversely related
Frequency and period
inversely related
Wavelength and frequency
inversely related
What happen when the power in an ultrasound beam is unchanged and at the same time the beam area doubles
it halved
Mathematically, when a number is squared the number is multiplied by
itself
What are the units of propagation speed
meters/second
What is the units of wavelength
millimeters
When a sonographer increases the maximum imaging depth during an exam what happen to the frequency
remains unchanged
What are the units of period
second
Frequency and intensity
unrelated
Frequency and sound speed
unrelated
Wavelength and intensity
unrelated
power and frequency
unrelated
The power of an ultrasound wave can be reported with which of the units
watts
