##### Chapter 2 Ultrasound - Notes

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1

Sound

phenomenon that is created by the vibration of a moving source

* a propagation variation in quantities called wave variables

* A traveling variation in wave variables

* A mechanical longitudinal (compressional) wave in which back and forth particle motion is parallel to the direction of wave travel

2

Sound Wave

longitudinal wave - particle motion is in the direction of wave motion.

3

How we create sound (talking)

Pressure variation in vocal cords propagating variation of acoustic variables.

4

Acoustic Variables

The propagation variations are called acoustic variables

*Pressure
*Density
*Temperature
*Particle motion

5

Repetitive Cyclical Particle Motion

As sound travels through a medium particles oscillate back and forth

Changes in:

*Pressure
*Density
*Particle Motion

6

Density

Acoustic variable

density = mass/volume

d = m/v

7

Density Units

kg/cm3

8

Pressure

Acoustic variable

pressure = force/area

p = F/A

9

Pressure Units

(Pa) pascals

10

Particle Motion units

distance

11

Wave

move matter but carry energy

traveling wave variation

A propagation variation in quantities called wave variables

12

Energy

is the ability to do work

13

Water Waves

Transverse wave

A traveling variation in wave variation

In water the variable is Height

14

Electromagnetic Wave

The variation is electrical energy - Photon

Can travel through a vacuum - No Matter

15

Can sound travel through a vacuum?

NO!!!

16

Do electromagnetic photons need material to travel?

NO

17

More stuff in the same amount of space =

A) less Pressure
B) More Pressure
C) Amount of stuff does not change pressure

B) More Pressure

18

More stuff in the same amount of space =

A) less Density
B) More Density
C) Amount of stuff does not change density

B) More Density

19

(Sound) mechanical longitudinal

A mechanical longitudinal (compressional) wave in which back and forth particle motion is parallel to the direction of wave travel.

medium series of interacting and connecting related particles

Disturbance in the medium

particle to particle, sound waves are interaction is in the direction of wave motion

20

Which direction is the particle motion moving in a longitudinal wave?

in the direction of wave travel

parallel to wave motion energy transfer in the direction of wave motion

think of a slinky

21

Which direction is the particle motion moving in a transverse wave?

perpendicular to the direction of wave travel

think of a rope

22

Rarefraction

low pressure & low density

23

Compression

high pressure & high density

24

In a longitudinal wave if the particles are moving east & west the wave is moving?

A) East & West
B) North & South
C) can't be determined

A) East & West

25

There must be a medium

Photons of electromagnetic energy can travel through a vacuum

Waves of mechanical vibrations can not!

Sound does not travel through a vacuum.

26

In a transverse wave if the particles are moving east & west the waves are moving?

A) East & West
B) North & South
C) can't be determined

B) North & South

27

Parameters that influence sound waves

frequency
period
amplitude
intensity
wavelength
propagation speed

28

Parameters determined by the sound source

frequency
period
amplitude
intensity
wavelength

29

Parameters determined by the medium

wavelength
propagation speed

30

Which parameter is determined by both, the sound source and the medium?

wavelength

31

How fast the sound travels

A) is dependent on the source
B) is dependent on the receiver
C) is dependent on the material
D) a combination of A & B
E) a combination of A & C

C) is dependent on the material

Propagation Speed - how fast the wave travels

32

How often a wave is produced

A) is dependent on the source
B) is dependent on the receiver
C) is dependent on the material
D) a combination of A & B
E) a combination of A & C

A) is dependent on the source

Frequency

33

How long of a time period between each wave

A) is dependent on the source
B) is dependent on the receiver
C) is dependent on the material
D) a combination of A & B
E) a combination of A & C

A) is dependent on the source

Period

34

The amount of force carried by the wave

A) is dependent on the source
B) is dependent on the receiver
C) is dependent on the material
D) a combination of A & B
E) a combination of A & C

A) is dependent on the source

Intensity - amount of force carried by the wave

35

The variation in distance during oscillation of an individual molecule

A) is dependent on the source
B) is dependent on the receiver
C) is dependent on the material
D) a combination of 1 & 2
E) a combination of 1 & 3

A) is dependent on the source

Amplitude

36

The variation in distance between each wave

A) is dependent on the source
B) is dependent on the receiver
C) is dependent on the material
D) a combination of A & B
E) a combination of A & C

E) a combination of A & C

Wave Length - variation in distance between each wave

37

Frequency

cycles per second

How many complete cycles of acoustic variation in 1 second

Units (Hz) Hertz

38

Frequency equation

Frequency = # of cycles/seconds = Hz

39

Frequency unit

(Hz) Hertz

40

Hz (Frequency) equation

Hz = # of cycles/sec

41

kHz equation

kHz = #/ms

42

MHz equation

MHz = #/μs

43

1000 cycles per sec

1 kHz

1 kilohertz

44

1,000,000 cycles per sec

1 MHz - 1000 kHz

1 Megahertz - 1000 kilohertz

45

Positive half cycle

compression

46

Negative half cycle

rarefraction

47

Frequency determined by

the sound source

the transducer set the frequency

48

Frequency has effect on

Depth

Axial Resolution - clarity

49

Can sonographer change the frequency?

No

Frequency is determined by the transducer. To change the frequency you must change the transducer.

50

frequency, resolution & depth

Higher frequency = best resolution

increase frequency to improve resolution

decrease frequency to go further but pay in resolution.

51

4 probes

2.5 MHz - deep - low f
5 MHz - used by echo
7.5 MHz - shallow - high f
10 MHz

52

If I hit you in the arm 1 time in ten seconds the "f" is

A) 10 Hz
B) .1 Hz
C) 1 Hz
D) 100 Hz
E) .01 Hz

B) .1 Hz

53

If I hit you in the arm 10 times in one seconds the "f" is

A) 10 Hz
B) .1 Hz
C) 1 Hz
D) 100 Hz
E) .01 Hz

A) 10 Hz

54

If I hit you in the arm 10 times in ten seconds the "f" is

A) 10 Hz
B) .1 Hz
C) 1 Hz
D) 100 Hz
E) .01 Hz

C) 1 Hz

55

Audible Range for elephants

Elephants can hear in infrasound

56

Audible Range for bats

Bats can hear in ultrasound

57

Which of the following is within the range of audible sound?

A) 30 MHz
B) 3 MHz
C) .3 MHz
D) .03 MHz
E) .003 MHz

E) .003 MHz

58

Period

one complete cycle occurring

reciprocal of frequency

59

Period Unit

common microseconds

μs

60

A period of 1 μs = a frequency of

A) 1 Hz
B) 1 kHz
C) 1 MHz
D) 1 μHz

C) 1 MHz

61

Period vs Frequency

Reciprocals

Period up - frequency down
Period down - frequency up

62

Propagation Speed

(c)

speed that a wave moves through a medium

discussed as the max value of acoustic variation within a medium

63

Units of Propagation speed

(M/s) meters per second
(mm/μs) millimeters per microsecond

1000 m/s = 1 mm/μs
1 m/s = 1000 mm/μs

64

Speed is a ______________ quantity

A) scaler
B) vector

A) scaler

Speed is a scaler quantity
Velocity is a vector quantity and denotes direction.

for speed direction is assumed so velocity is not needed - speed is used

65

If a plane moves at 540 meters / sec How many mm/ms

A) .00054 mm/ms
B) .54 mm/ms
C) 540 mm/ms
D) 540000 mm/ms

C) 540 mm/ms

66

If a plane moves at 540 meters / sec How many mm/μs

A) .00054 mm/μs
B) .54 mm/μs
C) 540 mm/μs
D) 540000 mm/μs

B) .54 mm/μs

67

Propagation speed is determined by

the medium

*stiffness
*density

68

If stiffness increases what happens to speed?

Speed increases

69

If density increases what happens to speed?

Speed decreases

70

Density

concentration of matter
more stuff in smaller space - greater density
less stuff in larger space - less density
More density = lower propagation speed

71

Elastisity

(1/stiffness)

resistance to compression
more stiff = higher propagation speed.

72

Which of the following should have the greatest propagation speed?

A) Fat
B) Bone
C) Muscle
D) Blood
E) Lung

B) Bone

73

propagation speed in soft tissue

Range
1.44 mm/μs to 1.64 mm/μs

Average
1.54 mm/μs = 1540 m/s

74

propagation speed in lung tissue

.5 mm/μs = 500 m/s

less density - less stiffness

75

propagation speed in Bone

4.08 mm/μs = 4080 m/s

more density - more stiffness

76

propagation speed in fat

1.45 mm/μs = 1450 m/s

less density - less stiffness

77

Propagation speed's relation to wavelength

Direct relationship

if the speed of transmission increases the wavelength increases

if the speed of transmission decreases the wavelength decreases

78

wavelength

λ (lambda)

amount of space occupied by one complete cycle

79

Wavelength units

(mm/μs) millimeter/microsecond

80

Typical values of wavelength

.1 mm/μs to .8 mm/μs

81

Can wavelength be change by sonographer

No

82

Will wavelength affect axial resolution?

Yes

83

Is wavelength affected by the source?

Yes

Wavelength is inversely related by frequency which is determined by the source

84

Is wavelength affected by the medium?

Yes

Wavelength is directly related by propagation speed which is determined by the medium

85

What determines the wavelength?

frequency - inversely
propagation speed - directly

86

If c increases - the sound

A) arrives sooner and is placed closer
B) arrives later and is placed closer
C) arrives sooner and is placed further
D) arrives later and is placed further

A) arrives sooner and is placed closer

87

A = B x C
if B increases

A) A increases
B) A decreases
C) C increases
D) C decreases

A) A increases

88

B = A/C
if A increases

A) B increases
B) B decreases
C) C increases
D) C decreases

A) B increases

89

B = A/C
if C increases

A) A increases
B) A decreases
C) B increases
D) B decreases

D) B decreases

90

λ of 5 MHz in soft tissue

A) .308 mm
B) 3.08 mm
C) 3.26 mm
D) .326 mm

A) .308 mm

1540 m - propagation speed in soft tissue

1540/5 = 308 m

= .308 mm

91

λ of 5 MHz in bone

A) 8.16 mm
B) .816 mm
C) 1.2 mm
D) 12 mm

B) .816 mm

4080 m propagation speed in bone

4080/5 = 816 m

= .816

92

If wavelength goes up

A) frequency goes up
B) frequency goes down
C) frequency must have gone up
D) frequency must have gone down

D) frequency must have gone down

93

As frequency goes up

A) wavelength goes down
B) Wavelength goes up
C) wavelength must have gone up
D) wavelength must have gone down

D) wavelength must have gone down

94

If wavelength goes up

A) Period goes up
B) Period goes down
C) Period must have gone down
D) Period must have gone up

D) Period must have gone up

95

If period goes up

A) Wavelength goes down
B) Wavelength goes up
C) Wavelength must have gone up
D) Wavelength must have gone down

C) Wavelength must have gone up

96

Original value .498 kHz

A) 498 MHz
B) 498 Hz
C) .000498 MHz
D) Both A & B
E) Both B & C

E) Both B & C

97

Pulsed Ultrasound

A few cycles of insonation

talking time & Listening time

98

Sinusoidal wave

single frequency of fundamental frequency or first hamonics

99

THI

Tissue Harmonics Imaging

Harmonics button improves image

100

Harmonics

A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc.

2 MHz =
1 = 2 MHz
2 = 4 MHz
3 = 6 MHz
4 = 8 MHz

101

Amplitude

strength of wave

102

Interference

two waves at the same location and same at the same instant in time, will combine to form a single wave.

103

Constructive interference

Two waves superpose to form a resultant wave of greater amplitude

Constructive interference happens when the two waves have the same compression and rarefraction

104

Destructive Interference

Two waves superpose to form a resultant wave of lower amplitude

Destructive interference happens when the two waves have the different compression and rarefraction

105

Continuous Wave

Very sensitive
cycles that repeat indefinitely
always transmitting and receiving

One element for transmitting (talking)
One element for receiving (listening)

This type of ultrasound has range ambiguity
Can not determine the depth from which the returning echoes are coming from

106

range ambiguity

Continuous Wave can not determine the depth from which the returning echoes are coming from

107

When is continuous wave used?

Echo - EKG
Vascular - transcranial doppler

108

Pulsed Ultrasound

Burst of sound

One element for transmitting (talking) & receiving (listening)

109

B -Mode

1. element hit with electricity
2. element jiggles creating a pulse of sound
3. switches to receive (stopwatch on)
4. echo returns (stopwatch stopped)
5. element determines the amplitude (strength) of returning echo
6. copulates a picture with speed and time of return

110

Pulsed Ultrasound Parameters

(PRF) Pulse Repetition Frequency
(PRP) Pulse Repetions Period
(PD) Pulse Duration
(SPL) Spatial Pulse Length

111

Pulse Duration

PD

The time it takes for 1 pulse to occur
Time from the start of one pulse to the end of the pulse

*Time a pulse is Transmitting (talking or "On")

112

Pulse duration units

PD = μs

f = MHz

113

Pulse Duration Equation

Pulse Duration = period x cycles
PD = n x t

Pulse Durations = # of cycles/frequency
PD = n/f

114

How many cycles average in Pulsed Duration in B-mode

2 - 3 cycles

115

How many cycles average in Pulse Doppler

5 - 10 cycles

116

Does Pulse Duration change with depth?

No

117

Can the sonographer change the pulse duration?

No

characteristic of a transducer

118

Which is not correct?

A) PD = period x cycles
B) Cycles = PD / Period
C) Period = PD / cycles
D) all are correct
D) none are correct

D) all are correct

119

F 5 MHz, 3 cycles = PD

A) .2 μsec
B) 2 μsec
C) .3 μsec
D) 6 sec
E) .6 μsec

E) .6 μsec

120

.133 μsec period x 2 cycles

A) 2.66 μsec
A) .266 μsec
A) 2.66 msec
A) .266 msec

A) .266 μsec

121

pd Relationsships

period up - pulse duration up

number of cycles up - pulse duration up

frequency up - pulse duration down

122

Pulse Repetition Period

PRP

includes transmitting (talking) and receiving (listening) time

Pulse duration plus listening time

time of the start of a pulse to the start of the next pulse

123

PRP Units

ms
milliseconds

124

What determines the PRP?

The source (transducer)

125

Can the sonographer adjust the PRP?

Yes

increase depth, increase LT - increase PRP
decrease depth, decrease LT - decrease PRP

126

PRP is .034 μs =

A) .000034 ms
B) 34 ms
C) 340 ms
D) 34,000 ms

A) .000034 ms

127

Pulse Repetition Frequency

PRF

The number of pulses that occur in one second.

128

relationship between PRF & PRP

Reciprocals

PRF = 1/PRP

PRP = 1/PRF

129

Can PRF be changed by the sonographer?

Yes

change the depth changes PRF

130

PRP is .034 μs PRF is

A) .0294 KHz
B) 29.4 KHz
C) .0294 MHz
D) 29,411 KHz

D) 29,411 KHz

131

PRF 10 KHz =

A) .1 ms
B) 100 μs
C) .0001 sec
D) answers 1 & 2
E) all of the above

E) all of the above

132

PRF range for Diagnotic Sonography?

A) infra sound
B) audible sound
C) ultra sounf

B) audible sound

133

Duty Factor

DF

fraction of time that pulsed ultrasound is on.

.01 - 1
1% - 100%

134

Duty factor equation

DF = pulsed duration /pulsed repetition period/100

DF - pd(μs)/PRP(μs)

135

Duty factor formula 2

DF = pulsed duration * pulsed repetition frequency*100

DF - pd(μs) * PRF μs

136

If the PRP is longer?

A) Duty factor is higher
B) Duty factor is lower
C) Duty factor is unchanged by PRP

B) Duty factor is lower

DF and PRP are inversely related

137

If the PD is longer?

A) Duty factor is higher
B) Duty factor is lower
C) Duty factor is unchanged by PD

A) Duty factor is higher

DF and Pd are directly related.

138

Spatial pulse Length

SPL

Length of space over which a pulse occurs

increases with wavelength
increases with number of cycles
decreases with increased frequency

139

What determines the Spatial pulse length?

source and the medium

140

Spatial pulse length - units

mm

141

Can SPL be changed by the sonographer?

NO

142

SPatial pulse length equation

Spatial pulse length = wavelength * How many waves in a pulse

SPL = λ * # of waves in pulse

Spatial pulse length = # * speed / Frequency

SPL = nc/F

143

5 MHz, soft tissue, 3 cycles SPL?

A) 9.24 mm
B) .924 mm
C) 15 mm
D) 4.62 mm

B) .924 mm

3 * 1.54 / 5

144

5 MHz, soft tissue, 1 cycles SPL?

A) 3.08 mm
B) .308 mm
C) 5 mm
D) 1.54 mm

B) .308 mm

1 * 1.54 / 5

145

2.5 MHz, soft tissue, 3 cycles SPL?

A) 1.848 mm
B) .308 mm
C) 7.5 mm
D) 1.54 mm

A) 1.848 mm

3 * 1.54 / 2.5

146

CW vs pulsed

propagation speed does not vary from continuous to pulsed

Frequency for CW is reported as though the duty factor is 100%

147

Magnitude

The strength of sound
the ability to do work
loudness in sound

148

Magnitude parameters

amplitude
intensity

149

Amplitude

How far a variable gets away from normal undesturbed valus

150

Peak to peak amplitude

max to min values

151

Energy

ability to do work

ultrasound energy is transmitted in the form of a beam

152

Power

The rate at which work is done

the rate at which energy is transmitted along the beam
the rate at which energy is transferred from one part of the system to another

How much movement / how much time

153

Beam area

The amount of material involved
Affected by beam width

154

Area units

cm2

155

Area is determined by

the transducer and how it focuses the beam

156

Intensity

the rate at which energy is transferred across a unit area of the beam

concentration of power in a beam

157

intensity units

watts/cm2

158

What happens to power when you triple the intensity

Power increases

159

Intensity equation

Intensity = Power (W) / area (cm2)

I = P/a

160

Relationship between intensity and area

inversely

Area increases intensity decreases

area decreases intensity increases

161

Relationship between intensity and amplitude

Proportional to amplitude squared

162

Is intensity uniform

NO

intensity varies across the sound beam

stronger in middle and weaker along edges.

163

Is intensity uniform in U/S?

No

intensity needs time to build and time to fall

intensity will be reported in carious ways in reguard to time and space

164

Spatial refers to?

A) physical space
B) time
C) time / space
D) space / time

A) physical space

165

Peak

the maximum value

166

Average

mean

167

Spatial Peak Intensity

maximum intensity that is measured in a space

168

Spatial Average Intensity

average intensity over the cross sectional area of the beam

169

Which represents the higher value?

A) Spatial average
B) spatial peak
C) spatial mean
D) spatial min
E) A & C

B) spatial peak

170

Beam uniformity coefficient

SP/SA factor

describes the spread of beam in space

unitless #

1 or greater

171

Temporal refers to

A) time
B) frequency
C) period
D) Space / time

A) time

172

Temporal Peak Intensity

TP

The peak intensity occuring during the highest cycle

173

Temporal average Intensity

TA

The average intensity occurring during one pulse repetition period PRP

174

Which represents the highest value?

A) temporal Average
B) Temporal Peak
C) pulse peak
D) Pulsed average
E) A and C

B) Temporal Peak
C) Pulse peak

175

PA relationship to TA

DF = TA/PA

176

What happens to TA & PA when Duty Factor increases?

TA increases

PA decreases

177

What happens to TA & PA when Duty Factor decreases?

TA decreases

PA increases

178

Pulse Average

PA

intensity averages over one pulse

only during on time

copulated during pulse duration

179

Im

Intensity averaged over the most intense half cycle.

180

What happens to duty factor when TA intensity goes up?

Duty factor goes up.

181

DF & TA relationship

directly related if one increases so does the other

182

DF & PA relationship

inversely related if one increases the other decreases

183

Which could be the same value?

A) TA & TP
B) SA & SP
C) TA & SA
D) TP & SP
E) PA & TA

E) PA & TA

184

Intensity in continuous wave

DF is 100%

SPPA = SPTA
SAPA = SATA

PA = SA

185

Six possible intensities

SPTP
Im
SPPA
SPTA
SATA

SATP
SPTP

Spelling - Toilet paper
Spelling - Pennsylvania
Spelling - Tatoos
Add a Sata at the end then add Im 2nd

186

Equation for intensity of continuous wave

TA = DF * PA

187

Unit of intensity

W/cm2

188

Intensity rule of thumb

If the temporal average is being considered the Duty factor must be multiplied

DF = TA/PA

TA = DF*PA

189

Attenuation

toll that waves have to pay to propagate

The decreases in amplitude & intensity as sound travels through a medium

Attenuation occurs with any unfocused beam in a medium

190

What causes attenuation?

absorption
reflection
heat

191

Units for attenuation

dB

192

Attenuation over distance

The longer the path the greater the attenuation.

193

Attenuation coefficient

amount of attenuation that the wave has to occur for every 1cm that the wave travels

dB/cm

194

What is the greatest attenuator?

Air

in order

Air
lung & bone
soft tissue
water

195

Amplification factors

3 dB = 2
6 dB = 4
9 dB = 8
10 dB = 10
20 dB = 100
30 dB = 1000

196

Attenuation factors

-3 dB = 1/2
-6 dB = 1/4
-9 dB = 1/8
-10 dB = 1/10
-20 dB = 1/100
-30 dB = 1/1000

197

Log of a #

The # of 10's multiplied to make that number

198

Decibel facts

Decibels are logs
3dB = 50%
10 dB = 10% its orginal
attenuation is calculated in dB

199

Original salary \$10 per/hour, 10 dB raise. What is the new salary?

A) \$10 per hour
B) \$1 per hour
C) \$100 per hour
D) \$ 20 per hour

C) \$100 per hour

200

Original salary \$10 per/hour, 3 dB raise. What is the new salary?

A) \$10 per hour
B) \$20 per hour
C) \$30 per hour
D) \$100 per hour

B) \$20 per hour

201

Original salary \$10 per/hour, 6 dB raise. What is the new salary?

A) \$10 per hour
B) \$20 per hour
C) \$40 per hour
D) \$100 per hour

C) \$40 per hour

202

Original salary \$10 per/hour, 13 dB raise. What is the new salary?

A) \$10 per hour
B) \$20 per hour
C) \$60 per hour
D) \$100 per hour
E) \$200 per hour

E) \$200 per hour

203

Original intensity 130 mW/cm2, 3 dB attenuation. What is the new intensity?

A) 6.5 mW/cm2
B) 13 mW/cm2
C) 65 mW/cm2
D) 130 mW/cm2
E) 260 mW/cm2

C) 65 mW/cm2

204

Original intensity 130 mW/cm2, 10 dB attenuation. What is the new intensity?

A) 6.5 mW/cm2
B) 13 mW/cm2
C) 65 mW/cm2
D) 130 mW/cm2
E) 260 mW/cm2

B) 13 mW/cm2

205

Original intensity 130 mW/cm2, 13 dB attenuation. What is the new intensity?

A) 6.5 mW/cm2
B) 10 mW/cm2
C) 1690 mW/cm2
D) 2600 mW/cm2
E) 260 mW/cm2

A) 6.5 mW/cm2

206

Original intensity 80 mW/cm2, 29 dB attenuation. What is the new intensity?

A) 3.2 mW/cm2
B) 1 mW/cm2
C) 10 mW/cm2
D) .1 mW/cm2
E) 260 mW/cm2

D) .1 mW/cm2

207

Original intensity 80 mW/cm2, 25 dB attenuation. What is the new intensity?

A) 4 mW/cm2
B) 2.56 mW/cm2
C) .2 mW/cm2
D) .256 mW/cm2
E) .326 mW/cm2

D) .256 mW/cm2

208

Relationship between attenuation and attenuation coefficient

attenuation coefficient increases - attenuation increases

attenuation coefficient decreases - attenuation decreases

209

Relationship between attenuation and path length

path length increases - attenuation increases

path length decreases - attenuation decreases

210

Attenuation coefficient for soft tissue

1/2 dB of attenuation per cm for each mHz of frequency

211

What happens with sound with 400 wavelength?

sound is gone

212

Total Attenuation equation

Attenuation = 1/2 * frequency (MHz) * pathlength cm

A = 1/2 * MHz * cm

213

Attenuation formula one way or round trip?

A) one way
B) round trip
C) depends

C) depends

214

Does a higher frequency probe suffee, more or less, than a low frequency probe?

more attenuation

higher frequency attenuates more so it stays on the surface. The use of a lower frequency probe will go to deeper depth because it attenuates less .... but loss of clarity with low frequency.

215

Original intensity 2500 mWcm2, 22 dB attenuation. What is the new intensty?

A) 25 mWcm2
B) 2.5 mWcm2
C) 125 mWcm2
D) 15.75 mWcm2

D) 15.75 mWcm2

216

Relationship between attenuation coefficient and frequency

direct relationship

Frequency increases - attenuation coefficient increases

Frequency decreases - attenuation coefficient decreases

217

Relationship between attenuation and frequency

direct relationship

Frequency increases - attenuation increases

Frequency decreases - attenuation decreases