Wave interference

Wave interference is the superposition of two or more waves, producing a resultant wave whose amplitude depends on their relative phases.

Superposition principle: A linear-system principle stating that combined inputs produce the sum of their individual responses. It explains why overlapping waves combine by adding their displacements.
Wave: A disturbance that propagates through space or a medium, transferring energy and momentum. Interference describes how multiple propagating disturbances combine.
Young's double-slit experiment: An experiment in which light passing through two slits produces alternating bright and dark fringes. Its fringes directly reveal interference from two coherent light paths.
Diffraction: The bending and spreading of waves around obstacles or through openings. Diffraction concerns wave spreading, while interference describes superposition; diffraction patterns arise through interference.
Newton's rings: Concentric light and dark rings formed by interference in the thin film between a curved surface and a flat plate. The rings map thickness-dependent phase differences in a thin air film.
Phase: A position within a repeating cycle, often expressed as an angle or fraction of a period. The phase difference between waves determines whether their displacements reinforce or cancel.
Amplitude: The maximum displacement or field strength of an oscillation from its equilibrium value. The amplitudes being combined determine the strength of the resultant wave.
Michelson interferometer: An optical instrument that compares light traveling along two paths and recombines it to produce interference. It measures tiny path-length changes through shifts in fringe position.
Reflection: The return of a wave from a boundary into the medium from which it came. Reflection changes a wave's path at a boundary rather than naming how overlapping waves combine.
Thin-film interference: Interference between waves reflected from the upper and lower boundaries of a thin material layer. Reflections acquire path and phase changes that create colors or alternating brightness.

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