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SPI Physics Board Review, 288 Questions and Correct Answers, Complete Solution 2024.
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SPI Physics Board Review, 288 Questionsand Correct Answers, Complete Solution
2024.
Metric notations: giga, mega, kilo, hecto, deca, deci, centi, milli, micro, and nano
10 to the... Giga 9, mega 6, kilo 3, hecto 2, deca 1, deci -1, centi -2, milli -3, micro -6, nano -9
Complimentary metric units: what goes with giga? Mega? Hecto? Deca?
Giga+nano
Mega+micro
Hecto+centi
Deca+deci
Sounds must travel though a (blank) it cant travel through a (blank)
Medium, vacuum
Sounds is a (blank) wave
Mechanical, longitudinal
What are the three acoustic variables? What are their units?
1. Pressure: force/area, pascals
2. Density: mass/volume, kg/cm3
3. Distance: cm, feet, miles
Transverse versus longitudinal wave
In a Transverse wave the particles move perpendicular to the direction of the wave (think ocean waves).
In longitudinal waves the particles move in the same direction as the wave (bunched up slinky).
Compressions versus rarefactions
Compressions are areas of increased pressure or density whereas rarefactions are areas of decreased
pressure or density
Acoustic Parameters: what do these do? What are the 7 with ultrasound?
Acoustic parameters describe the features of a particular wave (whereas acoustic variables determine
which waves are sound waves). The 7 acoustic variables we are concerned about with ultrasound are:
period, frequency, amplitude, power, intensity, speed and wavelength
Acoustic parameters: Period
Definition, units, determined by source or medium, can sonographer change it, relationships
,The time required to complete a single cycle.
Units: seconds, microseconds, hours, any unit of time.
Determined by: sound source
Changed by sonographer: no
Relationships: period and frequency are reciprocals (inverse relationship); when one goes up the other
goes down.
Acoustic Parameters: Frequency
Definition, units, determined by source or medium, can sonographer change it, typical values,
relationships, what does freq affect?
In DMU the frequency of a wave is the number of cycles of an acoustic variable that occur in one second.
Units: per second, 1/second = Hertz (Hertz is per second, 1,000/sec = kilohertz;
1,000,000/sec=megahertz).
Determined by sound source.
Changed by sonographer: no
Typical values 2 to 15 MHz
Relationships: frequency and period are inversely related.
Frequency affects penetration and axial resolution (image quality)
Ultrasound is a wave with a frequency greater than (blank) Hertz
20,000 Hz, (20kHz)
Audible sound is between (blank) and (blank) Hz
20 and 20,000 Hz
Infrasound is sound with frequncies less than (blank) Hz
Less than 20 Hz
What time of relationship are period and frequency? What are their equations? What are their
complimentary units?
Period and frequency are reciprocals, having an inverse relationship (as one goes up the other goes
down);
period (sec)=1/freq (Hz)
Freq (Hz) = 1/period (sec)
Freq (Hz) x period (sec) = 1
Complimentary units: sec & Hz; microseconds and MHz
What are the 3 bigness parameters which describe a sound beam's strength?
Amplitude, Power, Intensityl
Amplitude: what is it? Typical units? Determined by? Changed by sonographer?
Amplitude is the difference between the average value and the maximum value of an acoustic variable.
Units: the units of the acoustic variables - pascals (pressure), grams per cm cubed (density), and particle
,motion (units of distance); amplitude is usually expressed in decibels.
Determined by: sound source
Changed by sonographer: yes
What is peak-to-peak amplitude and how does it compare the amplitude?
Amplitude is the difference between the average value and the maximum vale of an acoustic variable.
Peak-to-peak amplitude is the difference between the maximum and minimum values of an acoustic
variable. Amplitude is half of the peak-to-peak amplitude.
Amplitude (blanks) as sound propagates through the body
Decreases
Power: what is it? Units? Determined by? Changed by sonographer?
Power is the rate that work is performed, or the rate of energy transfer.
Units: Watts
Determined by: source
Changed by sonographer: Yes
What is the relationship between power & amplitude? Equation &
Example: what happens to power if amplitude is tripled? Halved? Doubled?
Power is proportional to the wave's amplitude squared.
Power=amplitude squared
Example: if amplitude is tripled, power is increased by a factor of 9; if amplitude is halved, the power js
decreased by a factor of 4 (quartered); if amplitude is doubled, the power is increased by a factor of 4.
Intensity: what is it? Equation? Units? Determined by? Changed by sonographer? Typical values?
Intensity is the concentration of energy in a sound beam. Intensity depends on the power & cross-
sectional area of the beam.
Equation: intensity = power (watts)/beam area (cm squared)
Units: watts/cm squared; (watts is from power, cm squared is from beam area).
Determined by: sound source
Changed by sonographer: yes (since power can be changed by sonographer then intensity can also be
changed by the operator).
Typical values: 0.001 - 100 watts/cm squared
How are intensity and power related? What happens to intensity if power is doubled? Quartered?
Intensity and power are proportional, or directly related. If one goes up, so does the other.
If power is doubled, intensity doubles.
If power is quartered, intensity is quartered.
How are intensity and amplitude related? Explain why. What happens to intensity if amplitude is
doubled? Quartered?
Intensiry is proportional to amplitude squared. We know this because intensity is proportional to power,
and power is equal to amplitude squared; therefore intensity is equal to amplitude squared.
, If amplitude is doubled, the intensity is increased by a factor of four.
If amplitude is quartered, then intensity is reduced by a factor of 16
Wavelength: what is it? Units? Determined by? Changed by sonographer? Typical values? Equation
Wavelength is the length or distance of a single cycle.
Units: meters, mm, any unit of length.
Changed by sonographer: no (wavelength influences axial resolution-image quality).
Typical values: 0.1-0.8 mm (in soft tissue)
Equation: wavelength (mm)=propagation speed (mm/microsecond)/frequency (MHz)
Lambda = c/F
What is the propagation speed (c) in soft tissue?
1.54 mm/microsecond
1540 m/second
1.54 km/second
Higher frequencies mean (blank) wavelengths; lower frequencies mean (blank) wavelengths
Higher frequencies mean shorter wavelengths.
Lower frequencies mean longer wavelengths.
Rule for wavelength: in soft tissue, divide 1.54 mm/microsecond by (blank)
Rule for wavelength: in soft tissue, divide 1.54 mm/microsecond by frequency in MHz
Propagation Speed: what is it? Units? Determined by? Changed by sonographer? Typical values?
Equation?
Propagation speed is the rate that sound travels through a medium. Aka velocity or speed.
Units: meters per second, millimeters per microsecond.
Determined by: Medium only (density and stiffness).
Changed by sonographer: No
Typical values: 1.54 km/sec; 1540 m/s; 1.54 mm/microsecond
Equation: speed (m/s)=freq (Hz) x wavelength (meters)
Put these in order from slowest to gastest propagation speeds: bone, air, fat, soft tissue
Slowest in gas, fastest in solid so:
Slowest to fastest:
Air, fat, soft tissue, bone
Which travels faster through soft tissue: sound with a frequency or 5MHz or with a frequency of
1MHz?
They travel at the same speed because it is through the same medium. Regardless of frequency, all
sound travels at the same speed through a specific medium.
The stiffer the medium the (blank) the speed? The denser the medium the (blank) the speed?
What about compressiblity and elasticity?
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