C11/12 (Waves) Flashcards
What’s meant by a progressive wave
Is a mean of transfering energy from one place to another without a transfer of matter between the two points
What are the two types of progressive waves
Transverse
Longitudinal
What do mechanical waves rely on to transfer energy?
Matter
Do EM waves rely on matter to transverse energy
No
Transverse waves (definition)
The direction of oscillation of a wave is perpendicular to the direction of motion of the wave
Transverse waves (examples)
Em waves (light and radio waves)
String waves
Seismic waves
Water waves
What are the troughs and peaks of a transverse wave?
The points where the oscillating particles are at a maximum displacement from their equilibrium position
Longitudinal waves (definition)
The direction of oscillation of a wave is parallel to the direction of motion of the wave
Longitudinal waves (examples)
Sound waves
P-waves
What is alternative name for longitudinal waves
Compression waves
What does a longitudinal wave consist of?
Areas of compression and refraction
S
Displacement
Units (m)
Distance from equilibrium position in a particular direction; a vector so can have a postive or negative value
A
Amplitude
Units (m)
Maximum displacement from the equilibrium position
Lambda
Wavelength
Units (m)
Minimum displacement between 2 points in phase on adjacent waves
T
Peroid of oscialltion
Units (s)
Time taken for one oscillation
f
Frequency
Units (Hz)
Number of wavelengths passing a given point per unit time
v or c
Wave speed
Units (m/s)
Distance travelled by the wave per unit time
What can a Displacement-Distance graph be used to find?
The amplitude and wavelength of both types of waves
What can a Displacement-Time graph be used to find?
Find the Time period, amplitude and frequency of both types of waves
The wave equation
Velocity= Frequency x Wavelength
What is the equation of wave speed, including time peroid?
Velocity= Wavelength / Time peroid
Equation for Frequency
Frequency = 1 / Time period
What does phase difference describe
The difference between the displacement or particles on a wave, or the difference between the displacement of particles on different waves.
What is phase difference measured in
Degrees or radians
Each complete wave as 360° or 2pie radians
When will particles reach max positive displacement at the same time
If particles oscillate perfectly in step with each other, both reach max positive displacement at the same time, they are described as in place. Phase difference of zero.
If particles are separated by a whole wavelength we say
The phase difference is 360° or two pi radians.
If two wavelengths out what is the phase difference
Phase difference is four pi radians or 720° etc
Equation for phase difference
Phase difference equals distance divided by wavelength times by 360 for degrees or multiple by 2pi to get in radians
When does reflection occur
When wave changes direction at the boundary between 2 different media, remaining in the original medium (light reflecting off a mirrored surface).The light waves remain in the original medium (the air)
What does the rays of a diagram show
The rays direction of energy transfer and so the path taken by the wave
When does the law of reflection apply
Whenever waves are reflected
What does the law of reflection state
It states that the angle of incidence is equal to the angle of reflection
When a wave is reflected what happens to the wavelength and its frequency
It’s remains unchanged
When does refraction occur
Refraction occurs when a wave changes direction as it changes speed when it passes from one medium to another.
Whenever a wave refracts, is there ever some sort of reflection off the surface?
There is always some reflection off the surface (partial reflection)
In refraction if the wave slows down how will it refract?
It will refract towards the normal
If a wave speeds up how will it refract
It’s refracts away from the normal
Does refraction have an affect on the wavelength and frequency
Refraction has an affect on wavelength but not frequency. If a wave slows down its wavelength decreases and frequency remains unchanged and if a wave speed up its wavelength increases and frequency remains unchanged
Refractive index equation
Refractive index equals speed of light in a vacuum divided by the speed of wave (varies)
The greater the refractive index the more the light entering the material is…
Refracted towards the normal.
Refraction of water waves
Speed of water waves affected by changes in the depth of the water (easy way to investigate refraction of water waves). When a wave enters shallow water, it slows down and the wavelength gets shorter.
Diffraction
Is a property unique to waves.
When waves pass through a gap or travel around an obstacle, they spread out
What waves can be diffracted
And what wave properties change
All waves can be diffracted
Speed wavelength and frequency all remain unchanged
What determines how much a wave defracts
Depends on the relative sizes of the wavelength and the gap or obstacle
When is diffraction most significant
It will only occur is the wavelength is similar to the size of the gap or obstacle (the more similar they are the significant the diffraction is).
Polarisation
Polarisation means that the particles oscillate along one direction only, which means the wave is confined to a single plane.
Unpolarised light
Light that oscillates in many different planes
What type of waves can be polarised and why
Transverse only.
The particles in Longitudinal waves oscillation are always parallel to the direction of energy transfer, can’t be polarised. Their oscillation are already limited to only one plane (direction of energy transfer).
Partial polarisation
When transverse waves reflect off a surface, become partially polarised. Meaning there are more waves oscillating in one particular plane, but wave isn’t completely polarised.
Partial polarisation occurs on what type of surfaces
Non-metallic surfaces
Metallic surfaces reflect light with a variety of vibrational directions, such reflected light is unpolarized.
Intensity
The radiant power passing through a surface per unit area,
Measured in Wm^2
Equation for intensity
I= P/A
I= P/ 4 pi r^2
Where A is the surface area or a sphere
Diffraction
The spreading of waves when they pass through a gap or by an edge/ obstacle
Coherence
Two waves are said to be coherent if they have the same frequency and the same constant phase difference
Incoherence
If two waves don’t have the same frequency or a constant phase difference
Superposition
When two or more waves overlap, the resultant displacement at a point is equal to the sum of the individual displacement at that point
Constructive interference
When the crests/ troughs of 2 waves coincide, they combine to create an amplified wave.
(The 2 waves are in phase with each other, zero phase difference).
Destructive interference
Where the crests of one wave are aligned with the troughs of another, they cancel each other out (or lower ones amplitude).
The wave are out of phase (anti phase), have half a cycle difference from each other.
What can an interference pattern be produced from?
2 coherent wave sources
How to work out path difference
Measure distance of one source and the other (find difference)
(Should be a multiple of the wavelength)
When do constructive interference occur?
Whenever the path difference between coherent sources is n x wavelength (where n is a whole number)
When do destructive interferences occur?
When path difference between coherent sources is n x wavelength / 2
(n is a whole number)
