Unit 2: Waves Flashcards
What are progressive waves?
Progressive waves transfer energy without transferring matter.
What are transverse waves?
Transverse waves are waves which the direction of wave movement is perpendicular to the oscillations.
Water waves are an example
What are longitudinal waves?
Transverse waves are waves which the direction of wave movement is parallel to the oscillations.
Sound waves are an example
What is the amplitude?
Maximum displacement from equilibrium
What is polarisation?
Reducing of transverse waves oscillating in a particular direction as the other directions are absorbed by a polaroid.
What is a wavelength?
The minimum distance between 2 oscillating points in phase with each other
What is frequency?
The number of cycles per second
What is the period
The time taken for 1 complete cycle
How are frequency and period linked?
Period = 1/frequency
How can wave speed be calculated?
C=fλ
What is diffraction and how does it work?
Diffraction is the spreading of a wave when it passes through a slit or objects.
If the slit is larger than the wave length little diffraction occurs, however if the slit is the same size or smaller than the slit then the wave spread will be 180°
What is a diffraction grating? And what happens when a light source travels through them
Diffraction gratings are an opaque material that have many narrow equally spaced slots.
When a light source travels through a diffraction grating a pattern of bright fringes appears.
What is superposition and when does it occur?
Superposition occurs when 2 waves meet and its the interference between these 2 waves.
What is constructive interference?
Constructive interference is when 2 waves that are in phase meet, they will form an amplitude which is the sum of each individual amplitude.
What is destructive interference?
Destructive interference is when 2 waves which are out of phase meet and they will cause an amplitude of 0.
What are stationary waves?
Stationary waves are when 2 waves of equal frequency and amplitude, travelling in opposite directions interfere with each other causing them to superimpose.
What is the formula for Young’s Double Slit?
Wavelength =
Split separation x Fringe separation / Distance from split to screen
What is the formula for diffraction grating?
Order x Wavelength =
Split separation / sinθ
What is refraction?
Refraction is the change of speed of a wave within a new medium.
What is the refractive index?
The ratio to tell how you much slower a wave will trave when entering a medium
Its the
original speed/Final speed
n=c/v
What does a high refractive index tell you?
A high refractive index tells you that light travels slower and that light will bend more towards the normal.
What is Snell’s law?
n1sin(i) = n2sin(r)
What is the critical angle?
The critical angle is the angle of incidence which causes the light to refract along the boundary
What is the equation for critical angle?
Sinθ = n2/n1
What is total internal reflection?
When θ1 is greater than the critical angle then no light is refracted all light is reflected within the first medium
What are the conditions for Total Internal Reflection?
1) the light must be in the medium with a greater reflective index
2) angle of incidence must be greater than the critical angle
What is Total Internal Reflection used in and how?
It’s used within optic fibres to transfer data by using light and total internal reflection
How do optic fibres work?
Light travels through a medium which has a high refractive index, this medium is then covered by a cladding which has a lesser refractive index.
What are the different types of fibres?
Multimode fibres and monomode fibres
What are multimode fibres?
Multimode fibres are fibres which have multiple paths of light travelling within them each taking their own path.
What are monomode fibres?
Monomode fibres are fibres with only 1 path of light travelling through them
What is Multimode dispersion?
Multimode dispersion is the spreading of the individual paths of light in Multimode fibres as they overlap each other
How is Multimode dispersion countered?
Multimode fibres are limited to short distances to prevent the dispersion
How are constructive and destructive interferences shown?
Constructive:
nλ path difference or 0°/360° in phase
Destructive:
(n+1/2)λ path difference or 180° out of phase
