3. Waves Definitions Flashcards
Define amplitude
A wave’s maximum displacement from its equilibrium position
Define antinode
A position of maximum displacement in a stationary wave
Define cladding
A protective layer on an optical fibre to improve the tensile strength of the fibre, prevent scratching and to prevent 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
Define diffraction grating
A grating with hundreds of slits per millimetre, 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 a similar magnitude to their wavelength
Define electromagnetic 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. It is the inverse of the time period.
Define fringe spacing
The distance between adjacent bright fringes or two adjacent dark fringes
Define interference
The name given to the superposition of the 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.
Define laser
A light source that produces a collimated and coherent beam
Define longitudinal wave
A wave with oscillations that are parallel to the direction of energy propagation. Sound waves are an example of a longitudinal wave.
Define material dispersion
Waves of different wavelengths travel at slightly different speeds through an optical fibre and so reach the end of the fibre at slightly different times, causing pulse broadening. The use of monochromatic light fixes this.
Define modal dispersion
Waves enter an optical fibre a slightly different angles, meaning the distance each beam has to travel is slightly different. This leads to the beams reaching the end at different times and so causes pulse broadening.
Define node
A position of minimum displacement in a stationary wave
Define optical fibre
A thin glass fibre through which signals are passed through. Optical fibres usually have cladding surrounding them.
Define path difference
A measure of how far ahead a wave is compared to another wave, usually expressed in terms of the wavelength
Define phase difference
The difference in phase between two points on a wave. It is usually expressed in radians
Define phase
A measure of how far through the wave’s 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. This can only occur for transverse waves.
Define pulse broadening
The elongation of a signal passed down an optical fibre, commonly due to modal or material dispersion
Define 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.
Define Snell’s Law
A law linking a wave’s angle of incidence to its angle of refraction, with the use of the refractive indexes of the mediums involved.
Define speed of a wave
The product of a wave’s frequency and wavelength
Define stationary wave
A wave that stores, but does not transfer, energy
Define total internal reflection
An effect that occurs in optical fibres, where full reflection occurs at the inside boundary of the fibre, meaning no radiation passes out.
Define transverse wave
A wave with oscillations that are perpendicular to the direction of energy propagation. Electromagnetic waves are examples of transverse waves.
Define wavelength
The distance between two identical positions on two adjacent waves. It is commonly measured from peak to peak or trough to trough.
Define 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 bright and dark fringes.
