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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
What is the potential energy and kinetic energy of a wave when the displacement is max?
Potential=max Kinetic=0
26
What happens to the energy and amplitude of a wave when there is friction?
Total energy and amplitude decreases progressively Oscillation defined damped
27
What happens to the oscillation of a wave if mechanical energy is given periodically?
Oscillation increases in amplitude Oscillation defined forced
28
Where does interference of waves happen?
In a space where 2 or more waves propagate and overlap
29
What is constructive interference?
When the displacement of waves align so that they reinforce each other and result in a wave of greater amplitude Wave amplitudes are added
30
What is destructive interference?
When the displacement of waves align so that they destruct each other and result in a wave of lesser amplitude Waves amplitudes are subtracted
31
Can sound propagate in a vacuum?
No
32
What is sound?
The propagation of elastic mechanical waves in a material medium
33
What does the increase of air temperature do to the speed of sound?
Increases it
34
What does the decrease of air temperature do to the speed of sound?
Decrease it
35
What does the increase of air temperature do to the density?
Decreases it
36
What is sound characterised by?
Frequency Amplitude Intensity Speed
37
What is pitch linked with?
Frequency
38
In what range can humans hear sound waves?
20-20000 Hz
39
What can timbre be described as?
The color of sound
40
Example of what Timbre does?
Allows you to distinguish between different instruments when the same note is played
41
What does timbre depend on?
The form of vibration (number and amplitude of harmonic components)
42
What does the loudness of sound depend on?
Energy transported in the unit of time
43
What is loudness?
The intensity of acoustic sensation
44
What is loudness measured in?
Bel
45
When does the doppler effect occur?
When a sound source or an observer are in motion with respect to the medium in which the sound is propagated
46
How is the sound perceived if the source and observer come closer?
With a higher pitch
47
How is the sound perceived if the source and observer move away?
With a lower pitch
48
What is ultrasound?
Sound whose frequency exceeds the sensitivity limit of the human ear
49
How do ultrasounds with low wavelength propagate?
As straight rays, directional beam
50
3 applications of ultrasound
Producing heat in tisues Crushing kidney stones Eliminate tartar or revitalise nerves
51
What does ionising radiation do?
Eject electrons and break atomic bonds
52
What does non-ionising energy do?
Induce thermal and mechanical changes (cannot break atomic bonds)
53
Which rays on the electromagnetic spectrum are ionising?
Gamma rays X-rays
54
Which rays on the electromagnetic spectrum are non-ionising?
Ultraviolet Infrared Microwave Radio
55
Why are radio waves good for radio transmission?
Because they can bypass obstacles by diffraction
56
What is diffraction?
Deviation fo the wave propagation trajectory
57
Electromagnetic spectrum mnemonic
Red Monkeys In Vegas Usually X-ray Girls
58
2 applications for microwaves
Signal tranmission (phones) Production of heat (diathermy)
59
What is diathermy?
Microwaves used to create heat within tissues which is used to promote healing and reduce pain
60
2 application of infrared waves?
Heat therapy Infrared photography of blood vessels and inflamed tissues
61
What kind of emissions is common with infrared waves?
Thermal emission (energy emitted after the collision resulting from the thermal agitation the the molecules)
62
Which waves have lowest energy?
Radio
63
Which waves have highest energy?
Gamma rays
64
Which waves have longest wave length?
Radio waves
65
Which waves have shortest wave length?
Gamma rays
66
What do ultraviolet waves produce?
Thermal emissions from high temperature sources
67
Which kind of UV from the sun is largely absorbed by the atmosphere?
UVC
68
Do X-rays have mass and charge?
No neither
69
What are 2 mechanisms of x-rays emission?
Breaking radiation Characteristic emission
70
Haw are x-rays produced by a cathode and an anode?
The cathode metal spiral emits electrons by thermionic effect when heated Eelctrons are accelerated by an electric field between the anode an cathode
71
What does the penetration of x-rays depend on?
The atomic number
72
Why is the absorption of x-rays by bones different from other tissues?
Because they are made of calcium that has a high atomic number
73
4 ways of x-ray absorption
Diffusion Photoelectric effect Compton effect Pair production
74
What is CT short for?
Computerised axial tomography
75
What does CT use to made 3D radiological images?
X-rays and computere
76
What does a CT show?
The minimal differences in density between he different tissues of an organ
77
What is NMR short for?
Nuclear magnetic resonance
78
Why is NMR harmless?
Because there are no x-rays used
79
What NMR similar to?
MRI
80
How does MRI work?
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
What do tissues rich in water look like in MRI?
Lighter color
82
What do tissues poor in water look like in MRI?
Darker color
83
What is PET short for?
Position emission tomography
84
What do PET scans allow for?
Detection of cancer cells
85
What highlights the proliferations of cancer cells in PET scans?
Glucose analogue
86
What is SPECT short for?
Single photon emission computerised tomography
87
What does SPECT scanners emit?
Gamma radiation
88
What is the distinction between gamma rays and x-rays?
Way of production
89
What are gamma rays produced by?
Radioactive decay of unstable isotopes of iodine
90
What is braking radiation?
Electrons are decelerated by interacting with matter, like when electrons are deflected by atomic nuclei

Medical physics (10 decks)

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