Waves Flashcards
What does a progressive wave(moving wave) do?
A progressive wave carries out energy from one place to another without transferring any material.
What does a wave carry?
energy
What kind of waves heat things up?
Electromagnetic waves
what can be ______, ________ and _________
reflected, refracted and diffracted
what is reflection ?
the wave is bounced back when it hits a boundary
What kind of waves knock electrons out of their orbits, causing ionisation.
X-rays and gamma rays
What is refraction?
the wave changes direction as it enters a different medium. The change in direction is a result of the wave slowing down or speeding up
What wave power can be used?
generate electricity
What kind of waves make things vibrate?
loud sound waves
what is diffraction?
the wave spreads out as it passes through a gap or round an obstacle
what is the definition of displacement?
how far a point on the wave has moved from its undisturbed position
what is the definition of amplitude?
the maximum displacement
what is the definition of wavelength?
the length of one whole wave oscillation or wave cycle
what is the definition of period?
the time taken for one whole wave cycle
what is the definition of frequency?
the number of whole wave cycles per second passing a given point
what is wavelength measured in?
metres
what is the definition of phase difference?
the amount by which one wave lags behind another wave
what is phase difference measured in?
degrees or redians
what is the formula which links frequency and period together
f=1/t
what is the formula for wave speed?
c = d/t c = f入
what is a transverse wave?
the vibration is at right angles to the direction of travel.
examples of transverse waves?
electromagnetic wave ripples on water earthquake shock wave (S-waves)
what is the a longitudinal wave?
the vibrations are along the direction of travel, it consists of alternate compression and rarefactions.
examples of longitudinal wave
sound wave earthquake shock wave (P-wave)
what do we use to demonstrate longitudinal and transverse waves?
slinky
what are ordinary light waves?
ordinary light waves are a mixture of different directions of vibration.
What can we do to make the ordinary light waves travel in one direction?
polarise the oridinary waves
what can we use to polarise the ordinary light waves?
polarising filter
whatwould happen if you have two polarising filters at right angles to each other?
no light will get through
what kind of wave can be polarised?
transverse waves
examples of polarisation of light?
glare reduction
What would happen to the light reflected by a glass block?
reflected light is partially polarised
what would happen if you let partially-polarised reflected light travel through a polarising filter at right angle ?
it would block out most of the reflected light, while still letting through light which vibrates at the angel of the filter.
Why light goes faster in vacuum but slower in other materials?
because it interacts with the particles in them
the more ____________ a material is, the more light _________ when it enters it.
optically dense, slows down
how do we measure optical density?
refractive index
the higher a material’s __________ is, the _________ its ______________.
optical density, higher, reflective index
what is the formula for reflective index?
n=c/cs
which is the angle of incidence
the angle between incident ray and normal
which is the angle of refrction
the angle between refracted ray and normal
how do we find the refractive index if we have the angles
snell’s law
how do we find the refractive index if we have the speed?
n = c/cs
how do we calculate critical angle?
sinx = n2/n1
what is TIP
at angles of incidence greater than the critical angle, refraction can’t happen. that means all the light is reflected back into the material.
can you sketch 3 TIR examples
what is an optical fibre?
an optical fibre is a very thin flexible tube of glass or plastic fibre that can carry light signals over long distances and round corners using TIR.
can you sketch the struture of an optical fibre? cladding core
can you describe what’s going in an optical fibre?
light is shone in at one end of the fibre. the fibre is so narrow that the light always hits the boundary between the fibre and cladding at an angle greater than critical angle. so all the light is totally internally reflected from boundary to boundary until it reaches the other end.
what do we use optical fibres for?
transmit phone and cable tv signals
what are the advantages of using optical fibres? (5)
- the signal can carry more information because light has a high frequency 2. the light doesn’t heat up the fibre - so almost no energy is lost as heat. 3. there is no electrical interference 4. they are much cheaper to produce 5. the signal can travel a long way, very quickly and with minimal signal loss.
signal degradation
…
when do superposition happen?
when two or more waves pass through each other.
can you draw three different superpositions?
the superposition of two or more waves can result in ______________
interference
what is a constructive interference
a bigger wave
what is a destructive interference
cancellation
can you draw two points that are in phase
2 points on a wave are in phase if they are both at the same point in the same wave cycle
what are the two ways to describe phase difference?
- the amount by which one wave lag behind the other 2. the difference between two points
what is a stationary wave?
the superposition of two progressive waves with the same frequency and amplitude, moving in opposite directions.
one major difference between stationary wave and progressive wave
no energy is transmitted by a stationary wave
resonant frequency
….
nodes
are points on the wave where the amplitude of vibration is zero
antinodes
are points of maximum amplitude
fundamental frequency
the stationary wave is vibrating at its lowest possible resonant frequency.
second harmonic or first overtone
it has twice the fundamental frequency
third harmonic
is three times the fundamental frequency
wavelength always goes up by ________ .
half
stationary microwaves
you can set up a stationary wave by reflecting a microwave beam at a metal plate. the superposition of the wave and its reflection produces a stationary wave. you can find the nodes and antinodes by moving the probe between the transmitter and reflecting plate. the meter or loudspeaker receives no signal at the nodes and maximum signal at the antinodes.
diffraction
the way that waves spread out as they come through a narrow gap or go round obstacles
the amount of diffraction depends on ____________.
the wavelength of the wave compared with the sixe of the gap.
when the gap is a lot bigger than the wavelength, diffraction is _______
unnoticeable
you get noticeable diffraction through a gap several wavelength ______.
wide
the most diffraction is when the gap is ______ as the wavelength.
the same
if the gap is _____ than the wavelength, the waves are mostly just ________.
reflected back
why we can’t see the person behind the door?
light passes through the doorway, it is passing through a gap around a few million times bigger than its wavelength - the amount of diffraction is tiny.
diffraction around obstacles
when a wave meets an obstacle, you get diffraction around the edges. behind the obstacle is a shadow, where the wave is blocked. the wider the obstacle compared with the wavelength of the wave, the less diffraction you get, and so the longer the shadow.
the diffraction of light
when light shone through a narrow slit will diffract and sometimes produces a diffraction pattern. monochromatic light is of a single wavelength (and also a single colour). the diffraction of light is shown by shining a laser beam through a very narrow slit onto a screen. you can alter the amount of diffraction by changing the width of the slit. if the wavelength of a light is roughly similar to the size of the aperture(slit), you get a diffraction pattern of light and dark fringes. the pattern has a bright central fringe with alternating dark and bright finges on either side of it. the narrower the slit, the wider and less intense the diffraction pattern. the fringe pattern is due to interference.
white light
is made up of a continuous range of wavelengths across the visible light spectrum.
laser light
is monochromatic - it has single wavelength and frequency and a single colour. you need to be careful using laser lights. laser beams are very powerful and could damage your eyesight, so you should always make sure you dont look directly at the beam.
two source interference
is when the waves from two sources interfere to produce a pattern
coherent
two waves are coherent if they have the same wavelength and frequency and a fixed phase difference between them. if a light source is coherent, the troughs and crests line up- this causes constructive interference and a very intense beam.
path difference
the amount by which the path travelled by one wave is longer than the path travelled by the other wave
double slit interference of light
you can’t arrange two separate coherent light sources because they might not be coherent with each other. a laser light is monochromatic and coherent light. you can create two coherent light source by shining a single laser through two slits
laser safety precautions
working with laser is very dangerous because laser light is focused into a very direct, powerful beam of monochromatic light. if you look at a laser beam directly, your eyes lens would focus it onto your retina, which would be permanently damaged. to make sure you don’t cause any damage while using lasers, make sure you never shine the laser towards a person are wearing laser safety goggles avoid shining the laser beam at a reflective surface have a warming sign on display turn the laser off when it’s not needed
the double-slit formula
w = wavelength x D/ s
w = the fringe spacing , D = the distace from the slits to the screen,
S = spacing between slits
the fringes are usually so tiny. How can we get a relatively acurrate value of it?
it’s easier to measure across several fringes then divide by the number of fringe widths between them
the difference of red and blue lights in diffraction patterns
describe the diffraction pattern of single slit
- the central fringe is twice as wide as each of the outer fringes
- the peak intensity of each fringe decreases with distance from the centre
- each of the outer fringes is the same width
- the outer fringes are much less intense than the central fringe
diffraction grating
a diffraction grating consists of a plate with many closely spaced parallel slits ruled on it.
