[AS] Waves Flashcards
What is a wave
A wave is the oscillation of particles or fields
What is a progressive wave
A moving wave which carries energy from one place to another without transferring any material
A wave is caused by …
Something making particles or fields oscillate(vibrate) at a source
What is the displacement of a wave?
How far a point on the wave has moved from its undisturbed position
What is the amplitude of a wave?
Maximum magnitude of displacement
What is the frequency of a wave? What’s the equation?
The number of cycles that pass a given point per second
F= 1/T
What is meant by phase difference?
The amount one waves lags behind another
What is refraction?
The wave changes direction as it enters a different medium
What is a transverse wave?
Vibrate at right angles to the direction of energy transfer
E.g. all electromagnetic waves
What is a longitudinal wave?
Vibrate along the direction of energy transfer
E.g. sound
What is polarisation?
Examples?
The filtering of transverse waves into just one plane of motion
Tv and radio signals
Polarisation is evidence that …..
Electromagnetic waves are transverse
What is superposition?
2 or more waves pass through each other
What happens during constructive interference?
Crest meets crest
Or
Trough meets trough
What happens during destructive interference?
Crest and trough cancel out
How do 2 points in phase on a wave interfere?
Constructively
What is meant by in phase?
They are both at the same point in the wave cycle
Phase difference of zero or 360 etc
What is meant by 2 point exactly out of phase?
2 points with a phase difference of 180 degrees
To get interference patterns the two sources must be coherent.
What does this mean?
Same wave length and frequency
What is a stationary wave?
(Progressive wave reflected at a boundary)
The superposition of two progressive waves with the same frequency moving in opposite directors.
Is energy transmitted by a stationary wave?
Will Mike ever dunk?😂
How can you demonstrate a stationary wave?
Setting up a driving oscillator at one end of a stretched string with the other end fixed
What is meant by resonant frequent?
The frequency needed to create a stationary wave
Do stationary on strings form oscillating loops?
Can Marcus dunk?🤗 (yes)
what is diffraction?
waves spread out as they go round cornors or through a narrow gap
when the gap is a lot bigger than the wavelength, diffraction is……
unnoticeable
when do you get the most diffraction?
when the gap is the same size as the wave length
what happens if the wavelength is much bigger the the gap?
mostly reflection
what do you see when demonstrating diffraction patterns with a monochromatic, coherent light source?
a central fringe, with dark and bright fringes alternating on either side
what do you see when demonstrating diffraction patterns with white light?
multicoloured fringes
what does light intensity mean
the number of photons
describe young double slit experiment in 3 points
shine a laser between 2 slits
slits need to be about the same size as the wavelength of the light
you get a pattern of light and dark fringes depending of whether there is constructive or destructive interference
what was youngs double slit experiment evidence for?
the wave nature of EM radiation
what happens the the interference patterns of waves when you increase the number of slits?
why?
they get sharper
there are more beams reinforcing the pattern
dsinX = n(wavelength)
what does n, X and d mean?
n = which order X = angle between zero order and n d = space between slits
What is refractive index a measure of?
The ratio of the speed of light in two materials
n = C/Cs
what does each letter mean?
n= refractive index C= speed of light in a vacuum Cs= speed of light in material
Where do you measure the angle of incidence between?
The incoming ray of light and the normal
How does the angle of refraction change when light enters an optically denser medium?
Refracted towards the normal
How does the angle of refraction change when light enters an optically less dense medium?
Refracted away from the normal
At what angle is light refracted along the boundary when light enters an optically less medium?
Critical angle
What happens when the angle of incidence is greater than the critical angle when entering an optically DENSER medium?
Nothing
What happens when the angle of incidence is greater than the critical angle when entering an optically LESS DENSE medium?
Total internal reflection
What must be true about the density of the materials for total internal reflection to happen?
The light enters an optically less dense medium
What is the refractive index of optical fibres?
HIGH
What is the refractive index of optical fibre cladding?
LOW
How does light move through a optical fibre?
Total internal reflection
How can signal degradation happen in an optical fibre?
Absorption, Dispersion
What is signal degradation by absorption?
Some of the signal’s energy is lost through absorption by the material,
reducing its amplitude
What is signal degradation by dispersion?
Signals disperse as they travel down the wire.
Broadened pulses overlap and interfere with each-other
What are the two types of dispersion?
Modal, Material
Describe modal dispersion
Light enters the wire at different angles, so they take different paths.
Describe material dispersion
Light of different wavelengths travels at different speeds through the wire
How can you prevent modal dispersion?
Using a “single-mode fibre”
How can you prevent material dispersion?
Using monochromatic light
How can you reduce signal degradation along an optical fibre?
An optical fibre repeater
boosts and regenerates the signal
