# Shared Flashcard Set

## Details

MIT 231
week 3 prep
25
Physics
01/23/2012

Term
 List four Acoustic variables
Definition
 pressure, density, temperature, paricle displacement.
Term
 Amplitude is __________ of frequency.
Definition
 independent
Term
 What is it called when two waves have both maximum and minimum amplitudes the same?
Definition
 in-phase waves
Term
 When are two waves out of phase?
Definition
 when the maximum and minimum amplitudes occur at different times
Term
 What is the difference between constructive and destructive interference?
Definition
 Constructive results in a new wave with a larger amplitude. Destructive interference results in a new wave with a smaller amplitude.
Term
 Define power, include the mathmatical equation.
Definition
 Power is the amount of work performed by the wave per unit of time. P=W/t
Term
 What is the unit of power?
Definition
 Watt (W)
Term
 True or False. Power cannot be adjusted by the technologist.
Definition
 False! Power CAN be adjusted by the technologist.
Term
 Power is a rate at which:a. amplitude is increasedb. time is decreasedc. energy is transferred to the media by the sound beamd. the amplitude of the beam decreases as the sound propagates
Definition
 c. rate at which energy is transferred to the media by the sound beam.
Term
 Why is it recommended to the the power setting low on the US system?
Definition
 To avoid large transfer of energy into the tissue (heating).
Term
 power of the US beam ______ as the sound _______ through the tissue, because energy is lost.
Definition
 Decreases; Propagates. Power of the US beam decreases as the sound propagates through the tissue, because energy is lost.
Term
 True or False. Intensity is related to the pitch of the sound.
Definition
 False! Intensity is related to the loudness of the sound.
Term
 Write the equation for Intensity and the units used.
Definition
 I=P (power)/ Ar (area)Units is Watt/cm2
Term
 Name the maximum intensities for: Unfocused transducerFocused transducer
Definition
 Unfocused transducer- 100mW/cm2Focused transducer- 1W/cm2
Term
 What is Power proportional to?
Definition
 Intensity and Amplitude^2
Term
 If power is increased by the factor of nine, how does the amplitude of the wave change?
Definition
 Amplitude increases by a factor of 3
Term
 If amplitude is halved, how is the power changed?
Definition
 Power decreased by a factor of 4,
Term
 What is Intensity proportional to?
Definition
 Power and Amplitude^2
Term
 If power is doubled, what happens to intensity? amplitude?
Definition
 I increases by a factor of 2, A increases by a factor of squareroot of 2.
Term
 Log 100 is the same as what?
Definition
 10^y=100; 2
Term
 Complete the operations of log functions:  Log a+log b= Log a - log b= Log (ab)=
Definition
 Log a*b   Log a/b   b Log a
Term
 Explain the scale of Decibel. What does it represent?
Definition
 Decibel is a relative logrithmic scale. It represents a ratio of final or initial values.
Term
 Write the formula describing decibels.
Definition
 dB= 10 Log (Final Value/Initial Value)
Term
 A sonographer increases the output power by 3 dB. How did the power change in linear scale?
Definition
 dB= 10 Log Final/Initial 3dB= 10 log final/initial   .3=log Pfinal/Pinitial 10^(.3)=2   Answer is 2
Term
 Technologist increases the intesnity of the ultrasound by 6 dB. What is the increase in linear scale? What is the final intensity?
Definition
 6 dB=10 log Pf/Pi 10^(6)=Pf/Pi 4   There is an increase by a factor of 4.  The final intensity is undeterminable due to lack of information.
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