Amplitude: The maximum extent of a vibration or oscillation, measured from the position of equilibrium.
Antinode: The position of maximum displacement in a standing wave system.
Node: A point at which the amplitude of vibration in a standing wave system is zero.
Beat frequency: The number of beats per second, equal to the difference in the frequencies of two interacting tones or oscillations.
Frequency: The rate per second of a vibration constituting a wave.
Fundamental frequency (1st harmonic): The lowest frequency which is produced by the oscillation of the whole of an object, as distinct from the harmonics of higher frequency.
Period: The interval of time between successive occurrences of the same state in an oscillatory or cyclic phenomenon, such as a mechanical vibration.
Pitch: The quality of sound governed by the rate of vibrations producing. The degree of 'highness' or 'lowness' of a tone.
Resonant frequency: The natural frequency of vibration determined by the physical features of the vibrating object.
Standing wave: A vibration in a system in which some points remain fixed while others between them vibrate at the maximum amplitude.
Standing waves in closed pipes: A standing wave produced in a pipe with one end closed; nodes occur at the centre of the closed end and the edge of the open end.
Standing waves in open pipes: A standing wave produced in a pipe open at both ends; nodes occur at the edges of the open ends.
Standing waves in strings: A standing wave caused by the interference of two or more waves along a string.
String density: The mass per unit of length of a string. Strings with higher density have a lower resonant frequency.
String tension: A pulling force experienced along the length of a string. Higher tension leads to a higher resonant frequency.
Timbre: The perceived quality of a musical sound distinct from its pitch and loudness.
Wave types: Transverse waves have particle motion perpendicular to wave motion. Longitudinal waves have particles moving parallel to the wave direction.
Wavelength: The distance between successive crests of a wave
Wavespeed: The speed at which a wave travels; wave speed = frequency x wavelength.
Antinodal lines: Imaginary lines that connect the antinodes (points where the waves always interfere constructively).
Central bright fringe/ central maxima: The point in the centre of an interference pattern with zero path difference so all frequencies of light combine to form 'white' light.
Constructive interference: When two or more waves interfere such that their amplitudes combine/add together.
Destructive interference: When two or more waves interfere such that their amplitudes counteract/subtract from each other.
Diffraction: The process by which a system of waves is spread out as a result of passing through a narrow aperture or across an edge.
Diffraction grating: A band of equidistant, parallel lines ruled on a glass or polished metal surface for diffracting light to produce optical spectra.
Double slit: A type of diffraction grating with only two parallel lines to produce two beams of light, typically such that the beams interfere.
In phase: Describes two or more waves that reach the same positions (such as maximum amplitude) at the same time
Multiple-point source interference: Interference patterns produced by the interaction of multiple wave sources. For example, those produced by diffraction gratings.
Nodal lines: Imaginary lines connecting the nodes that occur in two-point source interference patterns.
Order number: Assigned to nodal and antinodal lines and equivalent to the path difference between wavefronts of two interfering waves.
Out of phase: Describes two or more waves with the same frequency that reach the same positions (such as maximum amplitude) at different times.
Path difference: The difference between the distances travelled by two waves meeting at a point.
Slit separation: The distance between successive slits in a diffraction grating.
Slit width: The distance between the edges of a slit in a diffraction grating.
Small-angle approximation: A useful simplification of some basic trigonometric functions which is approximately true where the angle is small (approaches zero).
Spectrum: A continuum of colour formed when a beam of white light is dispersed so that its component wavelengths are spread through different angles.
Two-point source interference: The interference of waves produced by two sources that are in phase.
Apparent frequency: The apparent upward or downward shift in frequency heard by an observer due to the movement of a wave source.
Apparent wavelength: The apparent shortening or lengthening of wavelengths reaching an observer due to the movement of a wave source.
Circular wavefronts: The shape of waves as a wave moves radially from a source (often represented in 2D for spherical wavefronts, e.g. light and sound).
Compressed wavefronts: Wavefronts that occur in front of a moving source
Doppler blue shift: Light waves that are compressed such that the wavelength of the source light shortens towards the blue end of the spectrum.
Doppler red shift: Light waves that are stretched such that the wavelength of the source light lengthens towards the red end of the spectrum.
Parallel: Describes lines, planes, or surfaces that are side by side and having the same distance continuously between them.
Perpendicular: Describes an angle of 90° to a given line, plane, or surface or to the ground.
Relative velocity: The velocity of something relative to something else that is moving, as compared to a fixed point.
Sonic boom: A loud explosive noise caused by the shock wave from an aircraft or other object travelling faster than the speed of sound.
Source (true) frequency: The actual frequency of a wave emitted by a source that will appear different to an observer if the source is moving relative to the observer.
Source (true) wavelength: The actual wavelength of a wave emitted by a source that will appear different to an observer if the source is moving relative to the observer.
Source velocity: The velocity of a source that is emitting a wave (light/sound).
Stretched wavefronts: Wavefronts that occur behind of a moving source
Tangential: Describes an imaginary (straight) line that passes some distance from an observer.
The Doppler Effect: The apparent change in frequency and wavelength of waves emitted by a moving source.
Wave equation: V = f λ (velocity equals wavelength multiplied by the frequency).
Wave velocity: The velocity of a wave as it propagates through a medium or field(s).