Waves Flashcards
wavelength
distance between the same points on two consecutive waves
amplitude
distance from equilibrium line to the maximum displacement (crest or trough)
frequency
number of waves that pass a single point per second
period
time taken for a whole wave to completely pass a single point
velocity =
velocity = frequency x wavelength
period =
period = 1/ frequency
increase frequency…
velocity increases
wavelength increases…
velocity increases
period is inversely/ directly proportional to frequency?
inversely
smaller period…
higher frequency, greater velocity
Transverse waves
- have peaks and troughs
- vibrations are at right angles to direction of travel
- e.g. light or any electromagnetic wave
Longitudinal waves
- have compressions and rarefactions
- vibrations are in the same direction as the direction of travel
- e.g. sound waves
measuring velocity: sound in air
- make a noise 50m from a solid wall, record time for the echo to be heard
- calc using speed=distance/time
OR - have two microphones connected to a datalogger at a large distance apart, record time difference between a sound passing one to the other
- calc using speed = distance/time
measuring velocity: ripples on water surface
- use a stroboscope (same frequency as water waves), measure distance between the ‘fixed rippes’
- calc using wave speed=frequency x wavelength
OR - move a pnecil along the paper at the same speed as a wavefront, measure the time taken to draw this line
- calc using speed=distance/time
waves can be…
refracted, reflected, absorbed or transmitted
reflection
- waves will reflect off a flat surface
- the smoother the surface, the stronger the reflection
- rough surfaces scatter the light so they appear not reflective
angle of incidence
angle of reflection
transmission
- waves will pass through a transparent material
- the more transparent, the more light will pass through
- it can still refract, but the process of passing through the material and still emerging is transmission
absorption
- if the frequency of light matches the energy levels of the electrons then the light will be absorbed by the electrons (and not reemitted)
- eventually they will be reemitted over time as heat
sound waves
- can travel through solids causing vibrations in it
- the outer ear collects the sounds and channels it down the ear canal as a pressure air wave
- the sound wave hits the ear drum
sound waves-once it hits the ear drum
- tightly stretched membrane which vibrates as the incoming pressure waves reach it
1. compression forces the eardrum inward and rarefaction forces the ear drum outwork due to pressure
2. the eardrum (and small bones connected) vibrate at the same frequency as the sound wave
3. vibrations of the bones transmitted to the fluid in the inner ear and compression waves are transferred to the fluid (in the cochlea)
4. the small bones act as an amplifier
5. as the fluid moves (bc of compression waves) the small hairs lining the cochlea move too, so when a certain frequency is recieved, the hair attuned to that frequency moves a lot
6. this releases an electrical impulse to the brain, interpreting this as a sound
humans cant hear below… or above… because
cant hear below 20Hz or above 20kHz because the hairs in the cochlea attuned to high frequencies die or get damaged (bc of loud noises, changes in inner ear, smoking, chemotherapy, diabetes etc)
Ultrasound
- when ultrasound reaches a boundary between two meida, they are partially reflected back
- the remainder of the waves continue and pass through + are refracted
- so a reciever next to the emitter can record the reflected waves
Ultrasound def
sounds higher than 20kHz (humans can’t hear)
infrasound def +use
sound wave with frequency lower than 20Hz (also known as seismis waves)
used to explore earth’s core
P waves
longitudinal, can pass through solids and liquids
S waves
transverse, only pass through solids (slower too)
sonar
- pulse of ultrasound is sent below a ship
- the time taken for it to reflect and reach the ship can help calculate the depth
- can be used to figure out if theres a shoal of fish under the ship or how far below the seabed is
electromagnetic waves order
radio
microwave
infrared
visible
ultraviolet
xray
gamma ray
electromagnetic waves
- transverse
- dont need particles to move
- in space, waves all have the same velocity
- can transfer energy from a source to absorber
Electromagnetic waves: relationships
as speed is constant for all EM waves
as wavelength decrease…
as frequency increases…
as wavelength decreases, frequency increases
as frequency increases, energy of the wave increases
refraction
- if entering a denser material, it bends towards the normal
- if entering a less dense material, it bends away from normal
- substances will absorb, transmit, reflect or refract certain EM waves depending on wavelength
refraction: some effects are due to differences in velocity
- when light enters a denser medium, it slows down
- shorter wavelengths slow down more than longer wavelengths
Why does dispersion occurs of white light into a prism?
The different wavelengths refract a different amount,
and therefore spread out creating a rainbow effect
When refracting, the speed…
When refracting, the speed decreases and wavelength
decreases too in denser material, the horizontal lines
show the “wave-fronts” of the waves
radio waves
- produced by oscillations in electrical circuits
- when radio waves are absorbed they create an alternating current at the same frequency as the radio waves
when electrons move to a higher orbit…
when electrons move to a lower orbit…
if an electron gains enough energy it can…
so gamma rays originate from…
… the atom has absorbed EM radiation
… the atom has emitted EM radiation
… leave the atom to form an ion
… changes in the nucleus of an atom
Hazards of EM radiation + some solutions
UV - skin ages prematurely, increasing risk of skin cancer (use sun cream)
x ray and gamma - ionisation radiation can cause the mutation of genes = causing cancer (minimal exposure should be ensured)
uses of EM waves
radio - tv and radio
micro - satellite communication, cooking food
infrared - cooking food, infrered cameras
visible - fibre optics
UV - sun tanning, energy efficient lamps
x ray + gamma - medical imaging + treatment
Lenses:
- If light passes through centre of lens…
- Lenses are generally drawn as …
- Focal points are…
- Convex lenses can have …
- Concave lenses can only have…
- If light passes through centre of lens, it does not
change direction. - Lenses are generally drawn as a dashed vertical line
- Focal points are points either side of the lens which
light can converge at. - Convex lenses can have virtual or real images (appear
to be on same or opposite side as the real object
respectively). - Concave lenses can only have virtual images.
Concave lenses:
A concave lens “caves” inward
- They are thinner at the…
- Light appears to have come from…
A concave lens “caves” inward
- They are thinner at centre than at edges
- Spreads light outwards
- Light appears to have come from the focal point
Convex Lenses:
A convex lens is normally … at centre
- They focus light…
- Horizontal rays focus onto…
- Used for…
- Used to correct…
A convex lens is normally wider at centre
- They focus light inwards
- Horizontal rays focus onto focal point
- Used for magnifying glasses, binoculars
- Used to correct long-sightedness, as it focuses
the rays closer
visible light:
types of reflection:
specular
diffuse
specular - smooth surface gives a single reflection
diffuse - reflection off a rough surface causes scattering
colour filters
- works by the filter absorbing every other colour + only letting certain wavelength (colour) through
opaque colours:
An opaque object has colour, determined by the…
- Wavelengths which are not reflected are absorbed
o If all wavelengths reflect…
o If all wavelengths are absorbed…
o The wavelength which is absorbed =
An opaque object has colour, determined by the strength of reflection for different
wavelengths
- Wavelengths which are not reflected are absorbed
o If all wavelengths reflect, it is white in colour
o If all wavelengths are absorbed, it appears black
o The wavelength which is absorbed = the colour which it appears
Objects that transmit light are either
transparent or translucent
black body radiation and space:
All objects, regardless of temperature, emit and absorb…
- The hotter the body:
o The greater amount of… released per second
o The greater amount of … released
All objects, regardless of temperature, emit and absorb infrared radiation.
- The hotter the body:
o The greater amount of radiation released per second (more powerful)
o The greater amount of shorter-wavelength radiation released (waves with more
energy, like x-rays etc.)
black body def
A black body is an object that absorbs all the radiation it receives (does not transmit or reflect any)
- And therefore also emits all types of radiation
a body at constant temp…
It is still radiating/receiving radiation
- But it is absorbing radiation at the same rate as it is emitting it
- Increasing temperature?
o It is absorbing more energy than it emits
a body cooling down…
energy is released at a greater rate than it absorbs
earth:
Sun’s energy is mostly … by the earth’s atmosphere, and some is …
The amount of energy re-radiated and absorbed leads to…
Sun’s energy is mostly absorbed by the earth’s atmosphere, and some is reflected
- The amount of energy re-radiated and absorbed leads to Earth’s temperature.
