Waves Flashcards
2 types of waves
Mechanical waves
Electromagnetic waves
What kind of medium does a mechanical wave need to propagate?
An elastic medium (spring, sound waves, stone in water)
Is there a transfer of matter in a mechanical wave?
No
Definition of mechanical waves
Propagation of a perturbation
What happens during a mechanical wave?
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
Where can an electromagnetic wave propagate?
In a vacuum
Absence of matter
Electric field
Magnetic field
At which speed does electromagnetic waves propergate in a vacuum?
Speed of light
What does the speed of an electromagnetic wave depend on when not in a vacuum?
The dielectric medium
What are transverse waves?
Waves with vibrations perpendicular to the direction of the propagation of the wave (like an ocean wave)
What are longitudinal waves?
Waves with vibrations in the direction of the wave propagation (like a sound wave)
What is a mono-dimensional longitudinal wave?
Waves with propagation in 1 direction
What is a bi-dimensional longitudinal wave?
Waves with propagation in 2 directions
What is a three-dimensional longitudinal wave?
Waves with propagation in 3 directions
What is the wave from?
The surface reached by the vibration in an instant in time
What is the wave surface?
Surfaces whose points are equidistant to the equilibrium position
What shape do spherical waves have?
Concentric shapes
What shape does circular waves have?
Spherical degenerate into circumference
How do flat waves propagate?
Flat propagation
What are wave rays?
Trajectories perpendicular to the wave surfaces
What are harmonic waves?
Propagation of periodic perturbations
What is the period (T) of a wave?
Time interval after which the motion resumes the same properties
Formula for frequency
f=1/T
What is the wavelength of a wave?
The distance traveled in one period
What is the potential energy and kinetic energy of a wave when the displacement is 0?
Potential=0
Kinetic=max
What is the potential energy and kinetic energy of a wave when the displacement is max?
Potential=max
Kinetic=0
What happens to the energy and amplitude of a wave when there is friction?
Total energy and amplitude decreases progressively
Oscillation defined damped
What happens to the oscillation of a wave if mechanical energy is given periodically?
Oscillation increases in amplitude
Oscillation defined forced
Where does interference of waves happen?
In a space where 2 or more waves propagate and overlap
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
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
Can sound propagate in a vacuum?
No
What is sound?
The propagation of elastic mechanical waves in a material medium
What does the increase of air temperature do to the speed of sound?
Increases it
What does the decrease of air temperature do to the speed of sound?
Decrease it
What does the increase of air temperature do to the density?
Decreases it
What is sound characterised by?
Frequency
Amplitude
Intensity
Speed
What is pitch linked with?
Frequency
In what range can humans hear sound waves?
20-20000 Hz
What can timbre be described as?
The color of sound
Example of what Timbre does?
Allows you to distinguish between different instruments when the same note is played
What does timbre depend on?
The form of vibration (number and amplitude of harmonic components)
What does the loudness of sound depend on?
Energy transported in the unit of time
What is loudness?
The intensity of acoustic sensation
What is loudness measured in?
Bel
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
How is the sound perceived if the source and observer come closer?
With a higher pitch
How is the sound perceived if the source and observer move away?
With a lower pitch
What is ultrasound?
Sound whose frequency exceeds the sensitivity limit of the human ear
How do ultrasounds with low wavelength propagate?
As straight rays, directional beam
3 applications of ultrasound
Producing heat in tisues
Crushing kidney stones
Eliminate tartar or revitalise nerves
What does ionising radiation do?
Eject electrons and break atomic bonds
What does non-ionising energy do?
Induce thermal and mechanical changes (cannot break atomic bonds)
Which rays on the electromagnetic spectrum are ionising?
Gamma rays
X-rays
Which rays on the electromagnetic spectrum are non-ionising?
Ultraviolet
Infrared
Microwave
Radio
Why are radio waves good for radio transmission?
Because they can bypass obstacles by diffraction
What is diffraction?
Deviation fo the wave propagation trajectory
Electromagnetic spectrum mnemonic
Red Monkeys In Vegas Usually X-ray Girls
2 applications for microwaves
Signal tranmission (phones)
Production of heat (diathermy)
What is diathermy?
Microwaves used to create heat within tissues which is used to promote healing and reduce pain
2 application of infrared waves?
Heat therapy
Infrared photography of blood vessels and inflamed tissues
What kind of emissions is common with infrared waves?
Thermal emission (energy emitted after the collision resulting from the thermal agitation the the molecules)
Which waves have lowest energy?
Radio
Which waves have highest energy?
Gamma rays
Which waves have longest wave length?
Radio waves
Which waves have shortest wave length?
Gamma rays
What do ultraviolet waves produce?
Thermal emissions from high temperature sources
Which kind of UV from the sun is largely absorbed by the atmosphere?
UVC
Do X-rays have mass and charge?
No neither
What are 2 mechanisms of x-rays emission?
Breaking radiation
Characteristic emission
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
What does the penetration of x-rays depend on?
The atomic number
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
4 ways of x-ray absorption
Diffusion
Photoelectric effect
Compton effect
Pair production
What is CT short for?
Computerised axial tomography
What does CT use to made 3D radiological images?
X-rays and computere
What does a CT show?
The minimal differences in density between he different tissues of an organ
What is NMR short for?
Nuclear magnetic resonance
Why is NMR harmless?
Because there are no x-rays used
What NMR similar to?
MRI
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
What do tissues rich in water look like in MRI?
Lighter color
What do tissues poor in water look like in MRI?
Darker color
What is PET short for?
Position emission tomography
What do PET scans allow for?
Detection of cancer cells
What highlights the proliferations of cancer cells in PET scans?
Glucose analogue
What is SPECT short for?
Single photon emission computerised tomography
What does SPECT scanners emit?
Gamma radiation
What is the distinction between gamma rays and x-rays?
Way of production
What are gamma rays produced by?
Radioactive decay of unstable isotopes of iodine
What is braking radiation?
Electrons are decelerated by interacting with matter, like when electrons are deflected by atomic nuclei
