Flashcards in Physics Review Ch. 5, 6, 7 Deck (63)

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1

## How do you calculate intensity?

###
a beam's power divided by its area.

units: W/cm^2

2

## What are other names for normal incidence?

###
perpendicular

orthogonal

right angle

90 degrees

3

## Difference between normal and oblique incidence

###
normal incidence strikes the boundary at exactly 90 degrees

oblique incidence strikes the boundary at any angle other than 90 degrees (acute and obtuse)

4

## Define incidence intensity

### The sound waves intensity immediately before it strikes a boundary

5

## Define reflected intensity

### Is the intensity of the portion of the incident sound beam that, after striking a boundary, returns back from where it came

6

## Define transmission intensity

### Is the intensity of the portion of the incident beam that, after striking a boundary, continues forward in the same general direction that it was traveling

7

## IRC

### Intensity Reflection Coefficient; the percentage of intensity that bounces back, after it strikes the boundary between 2 media. (1%)

8

## ITC

### Intensity Transmission Coefficient; the percentage of intensity that passes in the forward direction between 2 media. (99%)

9

## Define Impedance

###
The acoustic resistance to sound traveling in a medium. Calculated by multiplying the density of a medium by the speed at which sound travels in the medium.

Units: rayls; Z

10

## Impedance-what is takes to achieve reflection

### Reflection of an ultrasound wave depends upon the difference in acoustic impedances of the two media at a boundary.

11

## Define specular reflectors

### When the boundary is smooth, the sound is reflected in only on direction in an organized manner

12

## Conservation of energy

###
Applies at the boundary between two media.

IRC + ITC = 100%

13

## Reflection and transmission with oblique incidence

### We cannot predict; it's too complex

14

## Define Refraction

### Is a change in direction of wave propagation when traveling from one medium to another

15

## Refraction occurs only when there is what?

###
1. Oblique Incidence. (not normal)

2. Different Propagation speeds between the media.

16

## What is refraction associated with?

### Transmission

17

## Attenuation

###
The decrease in intensity, power, and amplitude as sound travels.

Units: dB

18

## Attenuation is determined by?

###
1. Path length

2. Frequency of sound

19

## What three processes contribute to attenuation?

###
1. Reflection

2. Scattering

3. Absorption

20

## What is impedance determined by?

### Medium

21

## Define scattering

### Is the random redirection of sound in many directions. (Disorganized and chaotic)

22

## Define Rayleigh scattering

###
Is a special form of scattering that occurs when the structure's dimensions are much smaller than the beam's wavelength. (Organized and omnidirectional)

*omnidirectional-in all directions

23

## Relationship between scattering and frequency

### directly related; Rayleigh scattering is proportional to frequency^4

24

## Formula for Impedance

### Impedance (rayls) = density (kg/m^3) * prop. speed (m/s)

25

## Formula for IRC and ITC

### 100% = IRC + ITC

26

## What are other names for decibel notation?

###
relative measurement

comparison

ratio

logarithmic

27

## Half-Value Layer

###
Is the depth of tissue that results in 3 dB of attenuation to the intensity.

May be called: penetration depth, depth of penetration, and half-boundary layer

Units: cm

28

## Half-value layer thickness depends on what two factors?

###
1. The medium

2. The frequency of sound

29

## Half-Value Layer conditions

###
Thin Half Value:

-High frequency sound

-Media with high attenuation rate

Thick Half Value:

-Low frequency sound

-Media with low attenuation rate

30