Definitions

• Progressive wave

  Moving wave that carries energy from one point to another without transferring any matter
• Cycle

  One complete oscillation of the wave
• Displacement(waves)

  Distance a point on the wave has moved from its equilibrium position
• Amplitude

  Magnitude of displacement
• Wavelength

  Length between 2 adjacent points moving in phase
• Period

  Time taken for a wave cycle to complete/pass a given point
• Frequency

  Number of cycles (produced)/(passing a given point) per second
• Phase

  Measure of the position of a certain point along the wave cycle
• Phase difference

  Amount (one wave)/(one point on a wave) lags behind another
• In Phase

  Two (points on a wave)/(waves) have a phase difference of 0/2π/360°
• Anti-phase

  Two (points on a wave)/(waves) have a phase difference of π/180°
• Wave types

  • Transverse waves
  • Longitudinal waves
• Unpolarised wave

  Oscillations in all planes perpendicular to the direction of wave travel
• Polarised wave

  Oscillations in only one plane perpendicular to the direction of wave travel
• Partial plane polarisation


  Waves can also be polarised by reflection, where a proportion of the reflected light will oscillate more in the horizontal plane than the vertical plane
• Superposition

  When two or more waves arrive at a point, they interfere and the resultant displacement at that point is equal to the vector sum of their displacements
• Coherent waves

  Waves with the same frequency and wavelength, with a fixed phase difference
• Stationary waves

  The superposition of two progressive waves travelling along the same line with the same speed and frequency with similar amplitudes in opposite directions
• Resonant frequencies

  Frequencies at which there is an exact number of half wavelengths between the oscillator and boundary, reinforcing each other and creating a wave pattern
• Harmonics

  Wave patterns created at resonant frequencies
• Path Difference

  Difference in the distance travelled by two waves from their sources to the point where they meet
• Fringe spacing

  The distance between the centre of 2 adjacent bright/dark fringes
• Corpuscles

  "Light is made up of tiny particles" - Isaac Newton
• Monochromatic

  Light of one colour / 1 wavelength/ 1 frequency
• Zero order line

  The line of maximum brightness at the centre for monochromatic light [diffraction gratings only]
• First order line

  The lines on either side of the central (zero order) line where path difference = λ
• X-ray crystallogrphy

  Crystal acting as a diffraction grating for x-rays
• Optical density

  Density with respect to speed of light of a substance
• Refraction

  When light travels from one medium to another medium with a different optical density, its speed changes, causing its direction to change.

  Faster - away from the normal

  Slower - towards the normal
• Angle of incidence

  Angle between incident ray and normal
• Angle of refraction

  Angle between refracted ray and normal
• Wavefronts

  Imaginary lines connecting the crests of waves together
• Refractive index

  Measure of optical density. Ratio between speed of light in a vacuum (c) and the speed of light in that material (cₛ)
• Critical angle

  The angle of incidence when the angle of refraction is at the maximum angle and light is refracted along the boundary
• Total internal reflection

  When all the light is reflected back into the material and the angle of incidence is greater than the critical angle
• Optical fibres

  Thin cables/wires that use total internal reflection to transmit light
• Core

  Middle of the optical fibre, made of plastic/glass; medium that light travels through
• Cladding

  Outer part with lower refractive indexes than the core, protects the core from scratches which could let light escape, prevents crossover of touching cores to preventing loss of signal
• Signal degradation

  Signal travelling through an optical fibre can be degraded (by absorption or dispersion) causing information loss
• Absorption

  As the signal is travelling, some of its energy is lost through absorption by the material the core is made out of, resulting in amplitude reduction