Physics 2 quiz (rachel)

Length or distance of a single cycle

Wavelength

Unit for wavelength

Millimeters

Typical values for wavelength

.1-.8mm

Wavelength is determined by

Sound source and medium

Can wavelength be changed by sonographer

No

How are wavelength and frequency related

Inversely

Higher frequency=

Shorter wavelengths

Lower frequency=

Higher wavelengths

The rate that sound travels through medium

Propagation speed or speed of sound

Propagation speed units

Distance/time Mm/no

Typical value for propagation speed

1500-1600 meters per second

What is propagation determined by

Medium only

Can propagation speed by changed by sonographer

No

Air

330m/s

Lung

500m/s

Fat

1450 m/s

Soft tissue (average)

1,540m/s

Liver

1,550m/s

Kidney

1560m/s

Blood

1570m/s

Muscle

1600m/s

Tendon

1850m/s

Bone

3500m/s (2000-4000)

How are speed and wavelength related (7)

Directly related (7)

Sound in slow medium has ______ wavelength

Short

Sound in fast medium has _____ wavelength

Long

Two characteristics of medium that affect the speed of sound

Stiffness Density

How are density and speed related (8)

Inversely related (8)

Change in shape, ability of an object to resist compression

Stiffness

Describes the relative weight of a material

Density

Can make the biggest change

Stiffness

What can have the greatest effect on speed

Stiffness

What relationship does speed and stiffness have

Direct

Other words for density

Compressibility Density Elasticity

Bulks relationship with speed

Direct (not the same as stiffness but has the same effect on speed)

If stiffer=

Goes faster

If denser=

Goes slower

The higher the frequency=

The less penetration

Amplitude =

Squared

If the amplitude of a wave is increased to 3 times its original value, the intensity is increased by 6 times (True or false)

False would be 9

Does propagation do anything to frequency

No

Acoustic variables

Density Particle motion Pressure (Pretty dang dumb)

What will create the fastest speed of sound

Low density, high stiffness

When two waves overlap at the same location and at the same instant in time, they combine with each other. The result of overlap is the creation of a single, new wave

Interference

In phase

Constructive interference

Out of phase

Destructive interference

When peaks and troughs come together opposite times they cancel out and make a smaller wave

Destructive

When the amplitude is less than one of the original two waves

Out of phase

Any number represents the number "10s" that are multiplied together to create the original number

Logarithms

Comparing a new intensity to original

Logarithmic scale

Log of 100

2

Log of 1000

3

_____dB means two

3

The final intensity is twice as big as the original intensity

3dB

The final intensity is 4 times the original

6dB

The final intensity is 8 times the original

9dB

The final intensity is 10 times bigger than the original intensity

10dB

The final intensity is 100 times bigger than the original

20dB

If using negative number new intensity will be _______ than original

Smaller

Fallen to 1/2 the original value

-3dB

Means we have fallen to 1/4 original intensity

-6dB

Means we have fallen to 1/8 of the original value

-9dB

We have fallen to 1/10 of the original value

-10dB

We have fallen to 1/100 of the original value

-20dB

How many intensities do we need to calculate decibels

2 intensities

A single power increases from 1 watt to 100 watts. How is this expressed in decibels?

20dB

An ultrasound system is operating at 100% power and the power setting is 0dB. What would the power setting be when the system is operating at 50%

-3dB

A sound beam has increased from its initial intensity by a factor of 100. How is this described in decibel notation?

20dB

DB is a mathematical representation with a _______ scale

Logarithmic

The relative CHANGE in a sound beams intensity is measured in

Db

Intensity unit

Watts/cm^2

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

Attenuation

Further sound travels the ________ it gets

Weaker

Attenuation units

DB

Frequency and attenuation have what relationship (5)

Direct (5

Path length and attenuation have what relationship (3)

Direct (3)

Higher the frequency the ________ attenuation

More

More frequency travels _________ they attenuate

More

High frequency =

More attenuation Long pathway

For less attenuation you want

Short pathway Low frequency

For more attenuation you want

High frequency Long pathway

A 3MHz sound beam travels through two media. It attenuates 5dB in medium A and 6 dB in medium B. What is the total attenuation that sound beam undergoes as it travels through both media

11dB

3 processes that contribute to attenuation

Reflection Scattering Absorption

Sound dissipated in heat

Absorption

As sound strikes a boundary, a portion of the wave's energy may be redirected, or reflected, back to the sound source

Reflection

2 types of reflection

Specular & Diffuse

Back scatter

Diffuse

Reflectors form a smooth reflector (mirror) are specular and return in ONE direction

Specular

Occurs when the wavelength is much smaller than the irregularities in the boundary

Specular reflection

When are specular reflectors well seen

When the sound wave strikes the reflector at 90 degrees

Examples of specular boundaries

Diaphragm Walls of vessels

What is best for grey scale

90

When boundary is rough, reflected sound is disorganized and random (1)

Diffuse reflection (1)

Occurs when the boundary has irregularities that are approximately the same size as the sound's wavelength (6)

Diffuse reflection (6)

The distribution of sound randomly in all directions

Scattering

When does sound scatter

When the tissue interface is small; that is, equal to or less than the wavelength of the incident sound beam

Which sound beams scatter more

High frequency

If reflector is much smaller or wavelength is bigger

Raleigh scattering

Omni directional

Raleigh scattering

Rayleigh and frequency relationship

Proportional