waves Flashcards
define amplitude
a wave’s max displacement from its equilibrium position
define antinode
a position of max displacement in a stationary wave
define cladding
a protective layer on an optical fibre to improve the tensile strength of the fibre
what does cladding do?
prevents scratching and signal transfer between adjacent fibres
when are waves coherent?
when they have the same wavelength and frequency with a fixed phase difference between them
define diffraction grating
a grating with hundreds of slits per mm, resulting in sharper interference patterns
what are diffraction gratings used for?
calculating atomic spacing and to analyse elements
define diffraction
the spreading of waves as they pass through a gap of similar magnitude to their wavelength
define electromagnetic waves
waves that consist of perpenpendicular electric and magnetic oscillations
define frequency
the number of waves that pass a point in a time period
define fringe spacing
the distance between two adjacent bright or two adjacent dark fringes.
define interference
the superposition of waves that occurs when two waves meet
what interference occurs when waves are in phase?
constructive interference
what interference occurs when waves are out of phase?
destructive interference
define laser
a light source that produces a coherent monochromatic beam
define longitudinal wave
a wave with oscillations parallel to the direction of energy
give an example of a longitudinal wave
sound waves
define material dispersion
waves of different wavelengths travel at slightly different speeds through an optical fibre so they reach the end at different times
what does material dispersion cause?
pulse broadening
how would you fix material dispersion?
by using monochromatic light
define modal dispersion
waves enter an optical fibre at slightly different angles, meaning the distance each beam has to travel is slightly different
what does modal dispersion cause?
pulse broadening
define node
a position of min displacement in a stationary wave
define optical fibre
a thin glass fibre through which signals are passed through
define path difference
a measure of how far ahead a wave is compared to another wave.
define phase difference
the difference in phase between two points on a wave
define phase
a measure of how far through the waves cycle a given point on the wave is
define polarisation
the restriction of a wave so that it can oscilate in a single plane
what type of wave can polarisation occur for?
transverse waves
define pulse broadening
the elongation of a signal passed down an optical fibre
define refractive index, n
the ratio of the speed of light in a vacuum and in a given material
what is snell’s law
law linking the wave’s angle of incidence to the angle of refraction using the refractive indexes of the mediums involved.
define stationary wave
a wave that stores but doesn’t transfer energy
define total internal reflection
an effect that occurs in optical fibres, where full reflection occurs at the inside boundary of the fibre, so no radiation passes out.
define transverse wave
a wave with oscillations that are perpendicular to the direction of energy propagation
give an example of a transverse waves
electromagnetic waves
how to measure wavelength?
from peak to peak, or trough to trough
define wavelength
the distance between two identical positions on two adjacent waves.
