waves Flashcards
define a progressive wave
an oscillation of particles/fields in a medium that transfers energy from one point to another, without transferring material
give an equation for wave speed
c=fλ
give an equation for frequency, with relation to period.
f= 1/T
define a transverse wave
the direction of oscillation is perpendicular to the direction of motion of the energy. i.e. electromagnetic
what is a longitudinal wave
the direction of the oscillation is parallel to the direction of motion of the energy i.e. sound waves
define polarization, and give an application
only allowing a wave to oscillate on one plane,
van be used in sunglasses/aerials
state the equation for the law of reflection
θ1=θ2
state the equation for refractive index
n =c/c(s)
where c is the speed of light and c(s) is the speed of light in the material
give snell’s law of refraction
n(a)sinθ(a) = n(b)sinθ(b)
what properties are affected by refraction
wavelength varies, wave speed varies
what is the refractive index of air
1
what is total internal reflection
where no refraction occurs if the angle of incidence is greater than the critical angle
sinθ =n(b)/n(a)
describe step index optical fibres, and the use of their cladding
- thin glass fibres that fire signals made of light pulses
- light undergoes TIR, so no light escapes
- cladding has a lower refractive index to ensure TIR happens
- cladding acts as protection for thin fibre
what is modal dispersion?
when light rays enter a fibre at different angles causing them to take longer to reach the end.
what is material dispersion, and how do you prevent it?
when different wavelengths travel at different speeds resulting in them arriving at different times
(can be overcome by using monochromatic light)
what is diffraction
waves spreading out after passing through a gap with a similar size to the wavelength
Define monochromatic
Single wavelength
Define coherent
Constant phase difference
State a safety precaution when using a laser
dont look into the laser
State and explain the effect of using a laser with a shorter wavelength on the maxima spacing in Young’s double slit
Maxima closer together
use w=𝜆D/s
Use wave theory to explain how the fringe pattern is formed
Slits act as coherent sources Waves diffract at slits Waves superpose Bright patches: constructive Dark patches: destructive
State two requirements for two light sources to be coherent
Same wavelength
Same phase
Explain how Young’s double slit arrangement produces interference fringes, refer to width of first slit and coherence of second slits
Narrow single slit gives wide diffraction to ensure that both second slits are illuminated
Paths to second slits are of constant length giving constant phase difference
Light diffracted at slits and overlap and interfere
Where path lengths differ by whole number of wavelengths, constructive interference occurs producing a bright fringe
If Young’s double slit was carried out with red light and then with white light, how would the two differ?
Central fringe would be white
Dark fringes would be closer together
Side fringes are spectra
State two ways a diffraction pattern on single slit would change if the slit became narrower
Increased separation
Lower intensity
State and explain what happens to angle θ in λ = d sin θ when wavelength decreases?
Angle θ gets smaller
As path difference gets smaller
Why will total internal reflection occur when light ray travels from water into glass?
TIR only occurs when ray travels from higher n to lower n
State and explain an advantage of a smaller diameter core in a fibre optic
Reduce multipath
Which would cause poor resolution
Define amplitude of a wave
The maximum displacement of the wave from the equilibrium position
What is an S-wave?
A secondary wave that is transverse
What is a P-wave?
A primary wave that is longitudinal
What is a compression and a rarefaction?
A compression is an area of high pressure and a rarefaction is an area of low pressure
What is the principle of superposition?
This is when two waves overlap, they superpose. When two waves meet at a point the resultant displacement at that point is equal to the sum of the displacements of the individual waves.
