Waves Flashcards
Define amplitude
A wave’s maximum displacement from it’s equilibrium position
What is an Antinode?
A position of maximum displacement in a stationary wave
What is cladding?
A protective layer on an optical fibre to improve the tensile strength of the fibre. Prevents scratching and prevents signal transfer between adjacent fibres
Define coherence
Waves are coherent if they have the same wavelength and frequency, as well as there being a fixed phase difference between them
What is a diffraction grating?
A grating with hundreds of slits per mm, that results in sharper interference patterns. They are used to calculate atomic spacing and to analyse elements
Define diffraction
The spreading of waves as they pass through a gap of similar magnitude to their wavelength
What are electromagnetic (EM) waves?
Waves that consist of perpendicular electric and magnetic oscillations
Define frequency
The number of waves that pass a point in a unit time period. The inverse of the time period
What is fringe spacing?
The distance between two adjacent bright fringes, or two adjacent dark fringes
Define interference
The name given to the superposition of waves that occurs when two waves meet. If the waves are in phase they will constructively interfere, but if they are out of phase they will destructively interfere
What is a laser?
A light source that produces a collimated and coherent beam
What are Longitudinal waves? Provide an example
Waves that oscillate parallel to the direction of energy propagation. Sounds waves are an example
What is material dispersion? How can is be fixed?
Waves of different wavelengths travel at slightly different speeds through an optical fibre, so reach the end of the fibre at slightly different times - resulting in pulse broadening. The use of monochromatic light fixes this
What is modal dispersion? How can it be prevented?
Waves enter an optical fibre at slightly different angles, meaning the distance each beam has to travel is slightly different. This leads to the beams reaching the end of the fibre at slightly different times - causing pulse broadening. Can prevented by using a fibre with a very narrow core
What is a node?
A position of minimum displacement in a stationary wave
What is an optical fibre?
A thin glass fibre that signals are passed through. Usually have cladding surrounding them
Define phase difference
The difference in phase between two points on a wave. Usually expressed in radians
Define path difference
A measure of how far ahead a wave is compared to another wave, usually expressed in terms of wavelength
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 only oscillate in a single plane. Can only occur in transverse waves
What is pulse broadening?
The elongation of a signal passed down an optical fibre. Commonly due to material or modal dispersion
What is a refractive index?
A material property that is equal to the ratio between the speed of light in a vacuum, and the speed of light in a given material
What is Snell’s law?
A law linking a waves angle of incidence to its angle of refraction, with the use of the refractive indexes of the mediums involved
Define speed
The product of a waves frequency and wavelength
What is a stationary wave?
A wave that stores, but does not transfer energy
What is total internal reflection?
An effect where light, instead of passing into a medium of lower refractive index, is completely reflected by the boundary between the two materials. Occurs when the angle it approaches the boundary at is greater than, or equal to the critical angle
What is a transverse wave? Provide an example
A wave that oscillates perpendicular to the direction of energy propagation. EM waves are an example
What is meant by wavelength?
The distance between two identical positions on two adjacent waves. Commonly measured Peak to peak, or trough to trough
What is Young’s double-slit experiment?
An experiment that demonstrates the diffraction of light by passing monochromatic light across two narrow slits and observing the resulting pattern of dark and bright fringes
