Editing Phase (waves) (section)

===For sinusoids===
For sinusoidal signals, when the phase difference <math>\varphi(t)</math> is 180° (<math>\pi</math> radians), one says that the phases are ''opposite'', and that the signals are ''in antiphase''.  Then the signals have opposite signs, and [[interference (wave propagation)|destructive interference]] occurs.  
{{anchor|Reversal}}Conversely, a ''phase reversal'' or ''phase inversion'' implies a 180-degree phase shift.<ref>{{Cite web|url=https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm|title = Federal Standard 1037C: Glossary of Telecommunications Terms}}</ref>

{{anchor|Quadrature}}When the phase difference <math>\varphi(t)</math> is a quarter of turn (a right angle, {{nowrap|1=+90° = π/2}} or {{nowrap|1=−90° = 270° = −π/2 = 3π/2}}), sinusoidal signals are sometimes said to be in ''quadrature'', e.g., [[in-phase and quadrature components]] of a composite signal or even different signals (e.g., voltage and current).

If the frequencies are different, the phase difference <math>\varphi(t)</math> increases linearly with the argument <math>t</math>.  The periodic changes from reinforcement and opposition cause a phenomenon called [[beat (acoustics)|beating]].