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Medical physics > Waves > Flashcards

Waves Flashcards

1
Q

2 types of waves

A

Mechanical waves
Electromagnetic waves

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2
Q

What kind of medium does a mechanical wave need to propagate?

A

An elastic medium (spring, sound waves, stone in water)

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3
Q

Is there a transfer of matter in a mechanical wave?

A

No

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4
Q

Definition of mechanical waves

A

Propagation of a perturbation

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5
Q

What happens during a mechanical wave?

A

External force moves a particle away from equilibrium position
Perturbation propagates to nearby atoms
Reaction forces are generated which brings particle back to initial position

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6
Q

Where can an electromagnetic wave propagate?

A

In a vacuum
Absence of matter
Electric field
Magnetic field

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7
Q

At which speed does electromagnetic waves propergate in a vacuum?

A

Speed of light

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8
Q

What does the speed of an electromagnetic wave depend on when not in a vacuum?

A

The dielectric medium

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9
Q

What are transverse waves?

A

Waves with vibrations perpendicular to the direction of the propagation of the wave (like an ocean wave)

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10
Q

What are longitudinal waves?

A

Waves with vibrations in the direction of the wave propagation (like a sound wave)

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11
Q

What is a mono-dimensional longitudinal wave?

A

Waves with propagation in 1 direction

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12
Q

What is a bi-dimensional longitudinal wave?

A

Waves with propagation in 2 directions

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13
Q

What is a three-dimensional longitudinal wave?

A

Waves with propagation in 3 directions

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14
Q

What is the wave from?

A

The surface reached by the vibration in an instant in time

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15
Q

What is the wave surface?

A

Surfaces whose points are equidistant to the equilibrium position

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16
Q

What shape do spherical waves have?

A

Concentric shapes

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17
Q

What shape does circular waves have?

A

Spherical degenerate into circumference

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18
Q

How do flat waves propagate?

A

Flat propagation

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19
Q

What are wave rays?

A

Trajectories perpendicular to the wave surfaces

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20
Q

What are harmonic waves?

A

Propagation of periodic perturbations

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21
Q

What is the period (T) of a wave?

A

Time interval after which the motion resumes the same properties

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22
Q

Formula for frequency

A

f=1/T

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23
Q

What is the wavelength of a wave?

A

The distance traveled in one period

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24
Q

What is the potential energy and kinetic energy of a wave when the displacement is 0?

A

Potential=0
Kinetic=max

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25
Q

What is the potential energy and kinetic energy of a wave when the displacement is max?

A

Potential=max
Kinetic=0

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26
Q

What happens to the energy and amplitude of a wave when there is friction?

A

Total energy and amplitude decreases progressively
Oscillation defined damped

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27
Q

What happens to the oscillation of a wave if mechanical energy is given periodically?

A

Oscillation increases in amplitude
Oscillation defined forced

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28
Q

Where does interference of waves happen?

A

In a space where 2 or more waves propagate and overlap

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29
Q

What is constructive interference?

A

When the displacement of waves align so that they reinforce each other and result in a wave of greater amplitude
Wave amplitudes are added

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30
Q

What is destructive interference?

A

When the displacement of waves align so that they destruct each other and result in a wave of lesser amplitude
Waves amplitudes are subtracted

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31
Q

Can sound propagate in a vacuum?

A

No

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32
Q

What is sound?

A

The propagation of elastic mechanical waves in a material medium

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33
Q

What does the increase of air temperature do to the speed of sound?

A

Increases it

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34
Q

What does the decrease of air temperature do to the speed of sound?

A

Decrease it

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35
Q

What does the increase of air temperature do to the density?

A

Decreases it

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36
Q

What is sound characterised by?

A

Frequency
Amplitude
Intensity
Speed

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37
Q

What is pitch linked with?

A

Frequency

38
Q

In what range can humans hear sound waves?

A

20-20000 Hz

39
Q

What can timbre be described as?

A

The color of sound

40
Q

Example of what Timbre does?

A

Allows you to distinguish between different instruments when the same note is played

41
Q

What does timbre depend on?

A

The form of vibration (number and amplitude of harmonic components)

42
Q

What does the loudness of sound depend on?

A

Energy transported in the unit of time

43
Q

What is loudness?

A

The intensity of acoustic sensation

44
Q

What is loudness measured in?

A

Bel

45
Q

When does the doppler effect occur?

A

When a sound source or an observer are in motion with respect to the medium in which the sound is propagated

46
Q

How is the sound perceived if the source and observer come closer?

A

With a higher pitch

47
Q

How is the sound perceived if the source and observer move away?

A

With a lower pitch

48
Q

What is ultrasound?

A

Sound whose frequency exceeds the sensitivity limit of the human ear

49
Q

How do ultrasounds with low wavelength propagate?

A

As straight rays, directional beam

50
Q

3 applications of ultrasound

A

Producing heat in tisues
Crushing kidney stones
Eliminate tartar or revitalise nerves

51
Q

What does ionising radiation do?

A

Eject electrons and break atomic bonds

52
Q

What does non-ionising energy do?

A

Induce thermal and mechanical changes (cannot break atomic bonds)

53
Q

Which rays on the electromagnetic spectrum are ionising?

A

Gamma rays
X-rays

54
Q

Which rays on the electromagnetic spectrum are non-ionising?

A

Ultraviolet
Infrared
Microwave
Radio

55
Q

Why are radio waves good for radio transmission?

A

Because they can bypass obstacles by diffraction

56
Q

What is diffraction?

A

Deviation fo the wave propagation trajectory

57
Q

Electromagnetic spectrum mnemonic

A

Red Monkeys In Vegas Usually X-ray Girls

58
Q

2 applications for microwaves

A

Signal tranmission (phones)
Production of heat (diathermy)

59
Q

What is diathermy?

A

Microwaves used to create heat within tissues which is used to promote healing and reduce pain

60
Q

2 application of infrared waves?

A

Heat therapy
Infrared photography of blood vessels and inflamed tissues

61
Q

What kind of emissions is common with infrared waves?

A

Thermal emission (energy emitted after the collision resulting from the thermal agitation the the molecules)

62
Q

Which waves have lowest energy?

A

Radio

63
Q

Which waves have highest energy?

A

Gamma rays

64
Q

Which waves have longest wave length?

A

Radio waves

65
Q

Which waves have shortest wave length?

A

Gamma rays

66
Q

What do ultraviolet waves produce?

A

Thermal emissions from high temperature sources

67
Q

Which kind of UV from the sun is largely absorbed by the atmosphere?

A

UVC

68
Q

Do X-rays have mass and charge?

A

No neither

69
Q

What are 2 mechanisms of x-rays emission?

A

Breaking radiation
Characteristic emission

70
Q

Haw are x-rays produced by a cathode and an anode?

A

The cathode metal spiral emits electrons by thermionic effect when heated
Eelctrons are accelerated by an electric field between the anode an cathode

71
Q

What does the penetration of x-rays depend on?

A

The atomic number

72
Q

Why is the absorption of x-rays by bones different from other tissues?

A

Because they are made of calcium that has a high atomic number

73
Q

4 ways of x-ray absorption

A

Diffusion
Photoelectric effect
Compton effect
Pair production

74
Q

What is CT short for?

A

Computerised axial tomography

75
Q

What does CT use to made 3D radiological images?

A

X-rays and computere

76
Q

What does a CT show?

A

The minimal differences in density between he different tissues of an organ

77
Q

What is NMR short for?

A

Nuclear magnetic resonance

78
Q

Why is NMR harmless?

A

Because there are no x-rays used

79
Q

What NMR similar to?

A

MRI

80
Q

How does MRI work?

A

Patient is irradiated by a magnetic field, forces generated by the magnetic field will align the moments of the molecules inducing a temporary alternations of the nuclei

81
Q

What do tissues rich in water look like in MRI?

A

Lighter color

82
Q

What do tissues poor in water look like in MRI?

A

Darker color

83
Q

What is PET short for?

A

Position emission tomography

84
Q

What do PET scans allow for?

A

Detection of cancer cells

85
Q

What highlights the proliferations of cancer cells in PET scans?

A

Glucose analogue

86
Q

What is SPECT short for?

A

Single photon emission computerised tomography

87
Q

What does SPECT scanners emit?

A

Gamma radiation

88
Q

What is the distinction between gamma rays and x-rays?

A

Way of production

89
Q

What are gamma rays produced by?

A

Radioactive decay of unstable isotopes of iodine

90
Q

What is braking radiation?

A

Electrons are decelerated by interacting with matter, like when electrons are deflected by atomic nuclei

Medical physics (10 decks)

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