Waves Flashcards
What is a progressive wave?
a wave that carries energy from one place to another without transferring matter
What is frequency?
the number of oscillations per second
what is phase difference?
a measure of the difference in where the two waves are in their cycle
what is reflection?
when the wave bounces back when it hits a boundary
what is refraction?
when a wave changes direction as it enters a different medium
what are transverse waves?
- example?
a wave in which the particles vibrate perpendicularly to the direction of the wave’s travel.
-electromagnetic waves
what are longitudinal waves?
- example?
a wave where the particles oscillate parallel to the direction of wave travel
- sound waves
what is a polarised wave?
- this can only happen to what kind of wave?
wave that only vibrates in one plane
- transverse waves
what are polarisers used for?
sunglasses, television transmission and reception
explain how polaroid material works?
polaroid sheets are made of long molecules that run up and down the sheet. waves parallel to the molecules are absorbed and those perpendicular are transmitted.
what are stationary waves?
a wave formed when two progressive waves with the same frequency and wavelength are moving in opposite directions and interfere with each other
What are nodes?
points on a stationary wave that have zero amplitude
what are antinodes?
points on a stationary wave with maximum amplitude
what is the equation of the first harmonic?
f= (1/2L) x root T/μ
what is the principle of superposition?
when two or more waves meet at a point, the resulting displacement at that point is the sum of the individual displacements of each wave
what does coherence mean?
when two waves have the same frequency and wavelength and a fixed phase relation
what does monochromatic mean?
light of the same wavelength
how could you use a laser as a source of monochromatic light?
-what does this produce?
shine laser through two slits and they act like to identical sources of laser light
- a series of light and dark fringes corresponding to constructive or destructive interference
what is the equation for fringe spacing in a double slit experiment?
w= λD/s
What would the interference pattern look like if white light was used in a double slit experiment?
Bright white middle fringe and side fringes have a spectrum of visible colours, blue is nearer the centre and red further out as blue diffracts less than red.
What safety precautions must be taken when handling lasers?
-not point laser in people’s eyes
-wear protective eyewear
-use proper signage so that people understand that you are dealing with lasers
How has light been theorised over the years?
newton, huygen, young, einstein
- Newtons corpuscles (packets of light)
- Huygen’s waves (wavefront theory)
- Young’s double slit experiment (backed Huygen)
- Einstein’s photons, photoelectric effect (backed newton)
How can we observe interference in sound waves?
set up to sound sources (speakers) that play the same sound at the same time, by moving a microphone from one side to the other we can measure constructive and destructive interference by whether the noise is loud or quiet
-How is constructive interference shown on a diffraction grating?
-How is destructive interference shown on a diffraction grating?
-bright lines
-dark lines
what are orders?
position of maxima
what is the zero order?
the largest, brightest line in the middle
what happens in the grating as the number of slits increase?
sharper lines
what is the diffraction grating equation?
dsinθ=nλ
what happens to the diffraction pattern if we :
-increase the wavelength?
-increase the slit screen distance?
-patterns becomes more spread out
-pattern becomes less spread out
Why are diffraction gratings useful?
-used to separate wavelengths in light of diffrerent substances
- atomics spacing in crystals
what is the refractive index of a material?
the ratio of the speed of light in a vacuum to the speed of light in that material
what is the equation for refractive index?
n= c/c(subscript s)
what is snell’s law?
n₁sinθ=n₂sinθ
what happens when light travels from a less optically dense medium to a more optically dense material?
it bends towards the normal
what happens when light travels from a more optically dense material to a less optically dense material?
it bends away from the normal
what is the equation for the critical angle?
sinθ=n₂/n₁
where n₁ is more optically dense that n₂
what happens when the angle of incidence is larger or equal to the critical angle?
total internal reflection
what is are the features of cladding?
- it has a much lower optical density meaning there is a very small critical angle
-when does material dispersion occur?
-what does this cause?
-how do we solve this?
-when different wavelengths of light arrive at the end of fibre at different time
-pulse broadening, signal degradation
- use monochromatic light
-when does modal dispersion occur?
-what does this cause?
-how do we solve this?
-when waves take different paths in the fibre meaning they arrive at the end of the fibre at different times
-pulse broadening
-use of monomode fibre
-what is pulse absorption?
-how to we solve this?
-when the signal is absorbed by the material leading to a reduction in signal amplitude
-use of signal repeaters or boosters
Why does the presence of a water droplet on a reflection tube cause a reduction in the intensity of the light?
it prevents total internal reflection from occurring as it increases the critical angle.
causing refraction instead.
What is the pattern produced on a screen when a light source goes through a single slit?
- bright and dark fringes
- central fringe is significantly more intense
how has the pattern produced changed on a screen when a light source going through a single slit is now red instead of green?
-fringes are further apart
- wider central maximum
