p12 - waves Flashcards
two different types of waves
transverse and longitudinal
what do waves transfer?
energy (not matter)
what causes waves?
vibrations and oscillations
transverse waves
when the displacement is at right angles (up and down) to the direction of the wave (horizontally) so they cross at a perpendicular
longitudinal waves
when the direction of energy transfer is parallel to the direction of the wave
examples of transverse waves
UV, electromagnetic
what is it called when longitudinal waves are close together?
compressions
what is it called when longitudinal waves are further apart?
rarefactions
wavelength
- lambda
- the distance between two identical points on the wave
frequency
- hertz
- the number of waves per second
1 wave per second =
1 hertz
amplitude
the maximum displacement from the rest position/equilibrium
equation for frequency
number of waves/time(s)
wave equation
wave speed (m/s) = frequency (Hz) x wavelength (m)
v = fA
1 hertz =
1/second
time period
time needed for the wave to complete one full vibration
equation for period
period (s) = 1/ frequency (Hz)
speed of sound:
330 m/s
calculating frequency (period equation)
frequency (Hz) = 1/period (s)
reflected
- waves will reflect off a flat surface
- the smoother the surface, the stronger the reflected wave is
- rough surfaces scatter the light in all directions, so they appear matt and not reflective.
- angle of incidence = angle of reflection
- light will reflect if the object is opaque and is not absorbed by the material
> the electrons will absorb the light energy, then reemit it as a reflected wave
transmitted
- waves will pass through a transparent material
- the more transparent, the more light will pass through the material
- it can still refract, but the process of passing through the material and still emerging is
transmission
specular reflection
type of reflection we get from smooth, shiny surfaces
diffuse reflection
type of reflection we get from rough, matt surfaces
REQUIRED PRACTICAL: how does increasing the angle of incidence affect the ray of reflection?
three things that can happen when a wave meets an interface of a material
refection, refraction or transmission
what is the ray going into a mirror called?
incident ray
name of the angle to the normal before it is reflected
angle of incidence
law of reflection
angle of incidence = angle of reflection
refraction
when waves are transmitted from one medium to another and there’s a difference in the optical density of the two media
- only occurs if the wave approaches the light at an angle
- if the wave approaches straight on (along the normal) the wave may change speed but NOT direction
optically dense
normal
wave fronts
if it’s going from less optically dense to MORE optically dense:
the light will bend towards the normal (refracts more)
if the light is going from a more optically dense material to a LESS optically dense material:
then it bends the other way (away from normal)
REQUIRED PRACTICAL: investigating the refraction of light
speed of sound
human hearing range
20Hz - 20,000Hz
what are sounds above the human hearing range classified as?
ultrasound
ultrasound
what can happen when waves arrive at a boundary/material?
- reflected or partially reflected
- transmitted
- absorbed
- refracted
two common purposes for waves
- ultrasound
- seismic waves
when are soundwaves partially reflected?
when an ultrasound wave meets a boundary between two different materials
pulse of an ultrasound
when directed at an object, some of the wave is reflected back
uses of ultrasound
- medical imaging
- industrial imaging
- echo sounding
ultrasound in industrial imaging
- ultrasound waves enter the material
- usually then partially reflected back by the far side of the material
- if there’s a crack inside the material then it will be reflected sooner, indicating a flaw
- the depth of each feature of a flaw can be calculated using s = vt, which allows us to form an image of the flaw
ultrasound in medical imaging (pre-natal scanning of a foetus)
- ultrasound waves enter and pass through the body
- some of the wave is reflected back (echoes) each time it meets a boundary (PARTIAL REFLECTION)
- reflections from different boundaries at different depths return at different times
- the depth (distance) of each structure/boundary can be calculated using s = vt and can be used to construct an image
why is a gel added?
to avoid the ultrasound wave being reflected back at the skin surface, a gel is placed between the patient’s skin and the ultrasound probe
seismic waves
- shock waves that are produced whenever there is an earthquake
- can be detected using a seismometer
two different types of seismic waves
S-waves and P-waves
primary waves (P-waves)
- longitudinal waves
- can travel through solids and liquids and can therefore pass through all of the earth’s layers
- the density of the earth increases with depth so as the waves pass through the earth, they change speed and refract gradually
- when the waves experiences dramatic changes in the earth’s structure there is also a dramatic refraction of the wave
secondary waves (S-waves)
- transverse waves
- can ONLY travel through solids, so can’t pass through all layers of earth
- they are SLOWER than p-waves
- the density of the earth increases with depth, so as the s- waves pass through the mantle, they change speed and gradually refract
importance of seismic waves
- allow scientists to determine where the properties of the earth change dramatically
- helps comprehend the internal structure of the earth (depending on where there is a major refraction)
comparing p-waves and s-waves
P-waves are longitudinal whilst S-waves are transverse
P-waves can go through both solids and liquids but S- waves can only go through solids (the earth’s mantle) therefore they are much slower
Therefore p-waves can travel through all internal structures of the earth while s-waves are absorbed once they travel through the liquid
Both types of waves gradually refract when they encounter a dramatic change in the earth’s structure
Both are seismic waves that are produced when there are earthquakes
