Waves 1 Flashcards
What is a progressive wave?
An oscillation that travels through matter and transfers energy but not matter.
What happens when a progressive waves travels through a medium?
- The particles move from their equilibrium positions to a new position
- The particles in the medium exert forces on each other
- The particles experience restoring forces from their neighbours and return to the equilibrium positions
What are transverse waves?
The oscillations travel perpendicular to the direction of energy transfers.
They have peaks and troughs
What are longitudinal waves?
Oscillations travel parallel to the direction of energy transfer.
Comprised of compressions (areas of high pressure) and rarefactions (areas of low pressure).
What is displacement in a wave?
The distance from the equilibrium position in a particular direction, vector quantity.
What is amplitude?
Max displacement from the equilibrium position, vector quantity
What is wavelength?
Min distance between two points in phase on adjacent waves
What is the period of oscillation?
The time taken for one oscillation or time taken for wave to move one whole wavelength past a given point
What is frequency?
The number of wavelengths passing a given point per unit time
What is wave speed?
The distance travelled by the wave per unit time.
What do displacement-distance graphs show?
The displacement of the particles in the wave along the distance along the wave. Can be used to determine the wavelength and amplitude of both types of waves.
What is phase difference?
The difference between the displacements of particles along a wave (or on different waves). Depends on the separation of particles in terms of the wavelength.
What do displacement-time graphs show?
The displacement of a given particles of the medium varying with time. Looks the same for both types of waves.
What is reflection?
When a wave changes direction at a boundary between two different media, remaining in the original medium.
What is a ray?
The direction taken by a wave
What is the law of reflection?
The angle of incidence is equal to the angle of reflection.
What are wavefronts?
A line joining points of the wave which are in phase. The distance between wavefronts is equal to the wavelength of the wave.
What is refraction?
When a wave changes direction as it changes speed when it passes from one medium to another
What is partial reflection?
Some reflection off the surface when a wave refracts
Where will the wave refract when it slows down?
Towards the normal
Where will the wave refract when it speeds up?
Away from the normal
What happens to the wavelength when the wave refracts?
If the wave slows down, the wavelength decreases and vice versa.
Refraction of water waves:
When a water wave enters shallower water, it slows down as the wavelength gets shorter.
What is diffraction?
When waves pass through a gap or travel around an obstacle, they spread out.
What does diffraction depend on?
The size of the gap that the wave travels around/through. If the gap is similar to the wavelength, then the diffraction here is the largest.
What is polarisation?
Polarisation is when waves are confined to a single plane, so the particles oscillate along one direction only.
What is the plane of oscillation?
Contains the oscillation of the particles and the direction of travel of the wave.
What is partial polarisation?
When more waves are oscillating in one particular plane, but the wave is not completely plane polarised.
What is intensity?
Defined as the radiant power passing through a surface per unit area. I=P/A or I=P/4pir^2 for a wave travelling out from a source
What is the relationship between intensity and amplitude?
Intensity=k(amplitude^2)
- The intensity drops as the areas increases so the amplitude decreases
- This reduces the speed and also the KE
What are EM waves?
Transverse, their vibrations are changes in electrical and magnetic fields at right angles
How to polarise EM waves?
With polarising filters: each filter only allows waves with a certain orientation through.
What is refractive index?
n=c/v
- The angle at which the light refracts depends on the refractive index
What is the refraction law?
nsintheta=k
n1sintheta1=n2sintheta2
When does TIR occur?
- At the boundary between two different media when light strikes the boundary at a large enough angle to the normal.
What are the two conditions for TIR?
- The light must be travelling through a medium with a higher refractive index as it strikes the boundary with a medium with a lower refractive index
- The angle at which the light strikes the boundary must be above the critical angle which depends on the refractive index of the medium
What happens when the angle is less than the critical angle?
Refraction and partial reflection occurs
What happens when the angle is equal to the critical angle?
Light refracts along the boundary between two different media
What happens when the angle is larger than the critical angle?
TIR
