EX unit three: waves Flashcards
what types can waves be divided into?
mechanical waves and electromagnetic waves
mechanical waves
waves that need a material medium to travel through
electromagnetic waves
waves that can travel through a vacuum
what can waves transfer?
energy and information without transfer of matter
what types can mechanical waves be divided into?
transverse and longitudinal waves
transverse waves
the oscillations of the spring are perpendicular to the direction of energy transfer along the spring
longitudinal waves
the oscillations of the spring are parallel to the direction of energy transfer along the spring
when a wave travels above its rest position on a diagram is it positive or negative displacement?
positive
when a wave travels below its rest position on a diagram is it positive or negative displacement?
negative
define wavelength
the distance between corresponding points in the wave - one crest to the next crest in a transverse wave.
define amplitude
the maximum movement of particles from their resting or equilbrium position
what are wavefronts
a line where all the vibrations are in phase and the same distance from the source
what is the period of a wave
the time for one complete cycle of the wave, from wavelength to wavelength.
what is the frequency of the wave
the number of cycles the waves form per second
what is frequency measured in (provided the frequency is in seconds)
hertz (Hz)
frequency =
1 / period
wave speed =
frequency x wavelength
what is the symbol for wavespeed
v
what is the symbol for frequency
f
what is the symbol for wavelength
lamda λ
what is wavelength measured in
m
what is wave speed measured in
m/s
what is a ripple tank
a simple piece of apparatus that makes it possible to show how waves behave.
describe the movement of waves in a stationary vehicle’s engine. how does this affect the sound?
the soundwaves arrive as a series of equally spaced wavefronts. people in front or behind the vehicle hear a sound of the same frequency and wavelength.
describe the movement of waves in a moving vehicle’s engine. how does this affect the sound?
the soundwaves are no longer evenly spaced wavefronts, they will be compressed and have a shorter wavelength. this means they will have a higher frequency and the person hears a higher pitch. behind the car the soundwaves are spaced out and have a longer wavelength. this means they will have a lower frequency
what is the order of the electromagnetic spectrum
radio waves - microwaves - infrared - visible light - ultraviolet - xrays - gamma rays
does frequency increase or decrease along the electromagnetic spectrum
increase
does wavelength increase or decrease along the electromagnetic spectrum
decrease
what is the order of colours in the visible part of the electromagnetic spectrum?
red - orange - yellow - green - blue - indigo - violet
what are electromagnetic waves
transverse changes in the electric and magnetic fields in space.
uses of radiowaves
communication of information e.g. speech, radio, tv
what waves have the lowest frequencies and the longest wavelength
radio waves
uses of microwaves
heating food and satellite communciation.
uses of infrared
night vision cameras and heating devices.
uses of visible light
used by humans to see things and photography.
uses of ultraviolet
black lights and sterilising water
uses of x-rays
used to examine the internal structures of the body in medical diagnosis.
uses of gamma rays
sterilising medical equipment and treating cancer.
dangers of microwaves
they can directly heat internal body tissue
dangers of infrared
its readily absorbed by our skin and will cause burns
dangers of ultraviolet
skin cancers and can damage the eyes
dangers of x-rays
cell mutation and cancer
dangers of gamma rays
cell mutation and cancers
what is i in wave diagrams
angle of incidence
what is r in wave diagrams
angle of reflection
where is the normal drawn in wave diagrams
a construction line drawn at right angles to the mirror surface where rays of light strike it.
where are all angles measured
between rays of light and the normal
what is the law of reflection
angle of incidence = angle of reflection
what is refraction
the bending that happens when light travels from one material, like air, into another, like glass.
where does light travel more slowly
in denser materials, so glass, perspex and water.
when a light ray travels from air into glass (or similar substances) which way is the ray bent?
towards the normal
when a light ray travels out of glass (or similar substances) and into air which way is the wave bent?
away from the normal
what does the degree of bending/refraction depend on?
the material that the light is travelling into (and out of).
what is the refractive index
the property of the material that determines the amount of refraction.
what does n stand for
refractive index
what is the law of refraction
refractive index (n) = sin i / sin r
when does total internal reflection occur
when the angle of incidence is greater than the critical angle, and when light is travelling from a material in which it travels more slowly, towards a medium in which it travels more quickly.
refractive index (n) = (involving c)
1 / sin c
what is total internal reflection used in
optical fibres, used in digital communication and speech and video communication. also in endoscopes.
what type of wave are soundwaves
longitudinal
what speed do soundwaves travel at in air
340 m/s
what speed do soundwaves travel in water
1500 m/s
can soundwaves travel through a vacuum
no
what range of frequencies can the human ear detect?
20 Hz to 20,000 Hz`
what does the pitch of a sound depend on
how quickly the sound producing system is vibrating
how does a microphone and an oscillioscope work
a microphone converts soundwaves into electrical signals, small voltages that vary with time. an oscilloscope amplifies these voltages and produces a graph which shows how the voltages are changing with time.
if a sound is very loud, will its height/amplitude on an oscilloscope trace be high or low.
high
what type of wave are light waves
transverse
if the source that is creating a wave vibrates quickly…
it will produce a large number of waves each second, and will have a larger frequency
if the source that is creating a wave vibrates slowly…
it will produce a fewer number of waves each second, and will have a lower frequency.
describe a ripple tank
when the motor is turned on, the wooden bar vibrates creating a series of ripples or wavefronts on the surface of the water. a light placed above the tank creates patterns of the water waves on the floor. by observing the patterns we can see how the water waves are behaving
what do the typical wavelength in nanometers range from
400nm to 700nm
how much is 1nm
1 x 10 to the power of -9
properties of the EM spectrum
they all transfer energy
they are all transverse waves
they all travel at 300 000 000 m/s
they can all be reflected and refracted
what is the speed of light in a vacuum
300 000 000 m/s
how does the transmission of radiowaves work
they are emitted from a transformer and arrive at an aerial, they are detected and the information they carry can be received. televisions and FM radio waves with the shorter wavelengths to carry their signals.
why do microwaves have a metal screen that reflects the microwaves and keep them inside the oven
because they could heat human body tissue.
why are microwaves used in communication
the waves pass easily through the earth’s atmosphere and can carry signals to orbiting satellites. they are then passed onto their destinations or to other satellites.
what do all objects emit
infrared radiation
what is visible light used for
read compact discs and barcodes, and also can be sent along optical fibres and therefore can be used in endoscopes
what does the ozone layer absorb
UV light
what can x-rays do and not do
pass through soft body tissue but not through bones.
how would you investigate the refractive index for glass
use a ray box and a rectangular glass box. shine a ray of light onto one of the sides of the glass box, so that the ray emerges on the opposite side of the block. mark the directions of both rays. draw around the box and then remove it. using the marks draw in the line of the ray going through the box. draw the normal. measure he angles of i and r, and then use the equation to find n
when does TIR occur
when rays of light are travelling towards a boundary with a less optically dense medium. (a medium with a lower refractive index) and when i is greater than c.
how would you investigate TIR
use a semi-circular glass block and a ray box. direct the light through the centre of the straight side of the block, then decrease and increase the angle at which the ray strikes the flat edge of the glass block, so you can discover the smallest angle at which most light is refracted along the edge of the glass block. this is the critical angle.
how would you investigate the TIR in prisms
do the same experiment but shine it through a prism
what is a periscope that uses prisms to reflect the light called
a prismatic periscope
what makes up an optical fibre
a very thin piece of optical fibre composed of two different types of glass. the centre is made of a glass that has a high refractive index surrounded by a different type of glass with a lower refeactive index.
how do obtical fibres work
as theyre very narrow, light entering the inner core always strikes the boundary of the two glasses at an angle greater than the critical angle, so no light escapes.
how are optical fibres used in modern telecommunications
electrical signals are converted into light energy produced by tiny lasers, which send pulses (small amounts) of light into the ends of optical fibres. a light sensitive detector at the other end changes the pulse back into electrical signals which then flow into a telephone receiver (earpiece).
how would you investigate the speed of sound using echoes
stand 50m away from a large wall or building. band two pieces of wood together and listen for the echo. band the pieces of wood together each time you hear the echo. this will create a regular rhythm of claps. ask the friend to time you doing 20 claps, during this time the sound will have travelled, for example, 50m x 20 x 2, (to the wall and back 20 times) and you can dividet this distance by the time to work out the speed of sound)
how does echo sounding work
sound waves are emitted from the ship and travel to the seabed.
some of these waves are reflected from the seabed back up to the ship. equipment on the ship detects these sound waves.
the time it takes the waves to make this journey is measured.
knowing theis time, the depth of the sea below the ship can be calculated.
how do most sound waves we hear travel
usually in a straight line
if something vibrates faster, what happens to the frequency
it will produce a high frequency
if something vibrates slower, what happens to the frequency
it will produce a low frequency
what is an oscilloscope
it shows an image or representation of a wave. (even if it is longitudinal it will be shown as a transverse wave because we can then see it’s features like amplitude and frequency more easily)
what is the spread of frequencies that we can hear called
the audible range
how can you demonstrate the audible range (and how it narrows as we get older)
use a signal generator and a loudspeaker to produce sounds at different frequencies
if a drum is hit hard, lots of energy is transferred to it from the drum stick. the drum skin vibrates…
up and down with a large amplitude, creating sound waves with a large amplitude so we will hear a loud sound.
if a drum is hit gently, less energy is transferred from the drum stick, so the drum skin vibrates…
up and down but with a smaller amplitude, so smaller sound waves are produced and we hear this as quieter.
why can’t soundwaves travel through a vacuum
there are no particles to carry the vibrations
