Waves Flashcards
What is the order of the EM Spectrum from Shortest Wavelength, Highest Energy?
Gamma Rays, X-Rays, Ultraviolet Rays, Visible Light, Infra-red, Microwaves, Radio Waves
What is the equation for The Law of Malus?
Light intensity passing through filter (I) = Light intensity entering filter (I0) x cos^2(Angle between E-field of light and axis of filter(ø))
I = I0 cos^2(ø)
When Sunlight is reflected off of the ocean, what is the polarisation of the reflected sunlight?
Horizontal
What orientation must the polarising filters in sunglasses be set to (given that they are eliminating reflection from horizontal surfaces)?
Vertically Orientated
What is the equation for Wavespeed regarding Wavelength and Time Period?
c = λ / T
In the equation nλ = d sinθ, what does d represent?
The distance between slits
What is Fringe Separation?
The distance between adjacent maxima
The sound quality of a portable radio is improved by adjusting the orientation of the aerial. Why is this?
The radio waves from the transmitter are polarised
Which one of these waves cannot be polarised? : Radio, Ultraviolet, Microwave, Ultrasound
Ultrasound
What band of the EM Spectrum would a wavelength of 200nm belong to?
Ultraviolet
What is displacement?
The distance and direction of a particle from the equilibrium position
Define amplitude
Maximum displacement of a vibrating particle
What is the wavelength?
The shortest distance between two particles in phase
Define frequency
Number of wave cycles occurring each second
Define wave speed
Distance travelled by a wave each second
Define phase difference
The amount by which one wave lags behind another wave, measured in degrees or radians
Define path difference
The difference in the lengths of two waves, measured in metres
What are progressive waves?
Waves whose oscillations travel and transfer energy
What is a transverse wave?
A wave whose oscillations are perpendicular to the direction of travel
Are electromagnetic waves transverse or longitudinal?
Transverse
What is a longitudinal wave?
A wave whose oscillations are parallel to the direction of travel
Are sound waves transverse or longitudinal?
Longitudinal
What does it mean if a wave is polarised?
All the waves are oscillating in the same plane
Only ____ waves can be polarised
Transverse
How is polarisation applicable in regards to glare and cameras?
Is used in polaroid sunglasses sunglasses to reduce glare and in cameras to enhance the image
How is polarisation applied in regards to TV and radio signals?
Tv and radio signals are polarised by the direction of the rods on the transmitting aerial
How can you ensure that you receive a TV or radio signal well?
By ensuring the receiving aerial and the waves are in the same plane
What is superposition?
The point where waves meet
What is the total displacement at the point of superposition equal to?
The sum of the individual displacements
When does constructive interference occur?
When waves are in phase
When does destructive interference occur?
When waves are anti-phase
What is created when two peaks/troughs constructively interfere?
A double peak/trough
What is created when a peak meets a trough?
They destructively interfere, cancelling each other out to create a minimum point
What is a stationary wave?
A wave that stores energy instead of transferring it
What is the equation for the fundamental frequency of a wave on a string?
f = 1/2l × sqrt(T/μ)
What does raising the tension or shortening the length of the string do to its fundamental frequency?
Increases it
In Young’s Double Slit Experiment, when illuminated, what did the two double slits act as?
Coherent wave sources
What does it mean if a wave source is coherent?
The waves have the same frequency and a constant phase difference
In Young’s Double Slit Experiment, why is an interference pattern created?
The lights diffracts at the slits and they superpose - a combination of cosntrictive and destructive interference
What is the double slit formula, W = λD/s , in words?
Fringe spacing = (wavelength × distance from the screen) /distance between slits
How did Young’s Double Slit Experiment provide evidence for the wave nature of EM radiation?
Diffraction and interference are purely wave properties
What is diffraction?
The spreading out of waves when they pass through a gap or over an edge
What does the amount of diffraction depend on?
The gap width and the wavelength of the wave
In regards to diffraction, what happens if the gap is a lot bigger than the wavelength?
The diffraction is unnoticeable
In regards to diffraction, what happens if the gap is a bit wider than the wavelength?
Diffraction is noticeable
In regards to diffraction, what happens if the gap is the same size as the wavelength?
The diffraction is most noticeable
In regards to diffraction, what happens if the gap is smaller than the wavelength?
Most of the waves are reflected
What is intensity a measure of?
Power delivered per unit area
What effect will increasing the Slit width have on a diffraction pattern?
It will create an intense but narrow central maximum
What effect will decreasing the Slit width have on a diffraction pattern?
It will create a wider and less intense central maximum
What is refraction?
When a wave changes speed when it crosses into a new medium
If a wave passes into a medium that is more optically dense, what will happen?
The wave will slow down and bend towards the normal
If a wave passes into a medium that is less optically dense, what will happen?
The wave will speed up and bend away from the normal
What does a material’s refractive index refer to?
How optically dense the medium is
What is the absolute refractive index?
How much a medium slows down light, as a ratio
What is the equation for absolute refractive index?
n = c / c¹
What can we use to predict the angle of refraction for a given angle of incidence?
Snell’s Law
What is Snell’s Law?
n¹sin(θ¹) = n²sin(θ²)
In regards to refraction, what is the critical angle?
The angle for which the refracted just passes along the boundary line and beyond which all of the wave will be deflected
What is the angle of refraction at the critical angle?
90°
In regards to refraction, what happens if the angle of incidence is greater than the critical angle?
The ray is reflected back inside
What are the two conditions for Total Internal Reclection to occur?
● Light must travel from a more optically dense to a less optically dense medium.
● The angle of incidence of the light ray must exceed the critical angle.
Give three examples of uses of Total Internal Reflection for transferring signals
● High-speed Internet cables
● Medical imaging as endoscopes
● Engineering inspections to view hard to reach areas
What are the two main parts of step-index optical fibres?
● A core made of a high-refractive index material.
● Cladding made of a low-refractive index material.
In an optical fibre, what are three purposes of the cladding?
● Provides tensile strength so it doesn’t break when twisted.
● Prevents information transferring between different cores.
● Prevents core being damaged
Why must optical fibres be protected from scratches?
Water may get in or the angle at which the signal hits the boundary may change
What happens if water gets into an optical fibre?
● Refractive index increases
● TIR cannot occur
● Signal exits core
What might a scratch do to an optical fibre?
Alter the angle at which the signal interacts with the core’s boundary such that the angle is lowered below the critical angle, preventing TIR and causing signal loss outside of the fibre
In regards to waves, what is absorption?
When energy is lost as a signal travels through an optical fibre
In regards to waves, what does absorption cause?
A loss of amplitude but no effect on the frequency
In regards to waves, how can the effects of absorption be reduced?
By using an optical fibre repeater to boost the signal at periodic points
In an optical fibre, what is modal dispersion?
When multiple beams enter a fibre at different angles, causing them to undergo TIR a different number of times and making them reach the end at different times, creating pulse broadening.
In an optical fibre, what is material dispersion?
A consequence of a signal containing several different wavelengths so they travel at different speeds, causing pulse broadening
