Waves Flashcards
What is a progressive wave?
An oscillation that travels through matter.
What do progressive waves transfer?
All progressive wave transfer energy but not matter.
Example of a progressive wave
Sound waves- when someone talks to you, the vibration travel to your ear, not the air particles.
What is a transverse wave?
The oscillation or vibration are perpendicular to the direction of the energy transfer.
Examples of transverse waves:
Water waves
EM waves
Waves on a string
S waves
What is a longitudinal wave?
The oscillation are parallel to the direction of energy transfer.
Examples of longitudinal waves:
Sound waves
P waves
Displacement
The distance from the equilibrium position in a particular position. Can be negative or positive
Amplitude
Maximum displacement from equilibrium position/ can be positive or negative
Period of oscillation
The time taken from one oscillation.
Frequency
The number of wavelength passing a given point per unit of time.
Wave speed
The distance travelled by the wave per unit time
What is the wave equation
V=f λ
What is the equation for frequency?
F= 1/T
Define phase difference
The difference between the displacement of particles along a wave.
When are particles in phase?
When they are oscillating perfectly in step of each other- phase difference of zero
When are particles in Antiphase?
If particles are oscillating completely out of step with each other.
(one reaches maximum positive displacement whilst the other reaches maximum negative displacement)
The phase difference is 180
Using an oscilloscope to determine wave frequency.
Use a microphone to produce a trace on the screen. Count the squares to find the frequency
What is reflection?
When a wave changes direction at a boundary between two different media, remaining in the original medium.
State what is the law of reflection
The angle of incidence is equal to the angle of reflection.
Do any properties of a wave change when a wave is reflected?
No their wavelength and frequency stays the same.
What is refraction
When a wave changes direction as it changes speed when passing from one medium to another.
What happens if a wave slows down?
It refracts towards the normal
What happens if a wave speeds up?
It will refract away from the normal
How does refraction effect the properties of the wave?
Refraction effects the wavelength but not its frequency.
If the wave slows down, its wavelength decreases and frequency remains constant. Vice versa
When a wave enters shallower water what happens?
It slows down and the wavelength gets shorter.
Define diffraction.
When a wave passes through a gap, the wave spread out.
When is diffraction most effective?
When the size of the gap or obstacle is the same as the wavelength of the wave.
Define polarisation
When the particles are oscillating along one direction and confined to a single plane.
What waves can be polarised?
Transverse waves can, longitudinal cannot as they are already limited to one plane.
Define intensity
The radiant power passing through a surface per unit area.
What is the relationship between intensity and distance?
They are inversely proportional. The further they spread out, reduces the intensity.
When power is spread out uniformly in all directions, what is the relationship between intensity and the distance from the source?
Intensity is inversely proportional to the radius squared.
What is the relationship between intensity and amplitude?
Intensity is directly proportional to the amplitude squared.
What speed do EM waves travel?
The same as the speed of light.
How can EM waves be polarised?
Using polarisers. Each filter only allows waves with a particular orientation through.
Polarisation of light
When you rotate the second filter 90, no light is transmitted and the intensity falls to zero.
Define refracted index
The angle at which light refracts, depending on the property of the material.
Equation for refraction index
N=c/v
c= speed of light through a vacuum
v= speed through the material
n= refracted index
The greater the refracted index, the ____ the light entering the material is reflected towards the material.
More
Refraction law
nsin(theta) = constant
n1sin(theta)1=n2sin(theta)2
What is total internal reflection?
When the light strikes the boundary and the angle is so large that the light is totally internally reflected. All the light is reflected back into the original medium.
What are the two conditions required for TIR to occur:
- Light must be travelling through from high refracted index to low refracted index. Not the other way round
- The angle the light strikes must be above the critical angle.
What is critical angle?
The angle of incidence at the boundary between two media that will produce an angle of reflection of 90
The greater the refracted index, the ____ the critical angle is.
Smaller
When two waves meet, and where the waves overlap what happens?
They superpose, producing a single wave.
State the principle of superposition.
When two waves meet at a point, the resultant displacement at that point is equal to the sum of displacement of the individual waves.
What is interference?
When two progressive waves pass through each other they superpose and produce a resultant wave with a displacement equal to the sum of individual displacement from the two waves.
What are the two types of interference?
Constructive interference
Destructive interference
When does constructive interference occur?
If two waves are IN PHASE, their maximum positive displacement line up so it will create a resultant displacement with an increased amplitude.
When does destructive interference occur?
If two waves are in ANTIPHASE, their resultant displacement is smaller then their individual waves.
Define coherence
Waves emitted from two sources having a constant phase difference, two waves must have the same frequency.
At a maxima what happens?
Waves interfere constructively.
At minimum what happens?
Destructive interference.
Define path difference.
The difference in distance travelled by two waves from their source.
At a node what happens?
The displacement is zero
What happens at an antinode?
The greatest amplitude.
