Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.
Formula
The phase of an oscillation or wave refers to a sinusoidal function such as the following:
:x(t) = A\cdot \cos( 2 \pi f t + \theta )\,
:y(t) = A\cdot \sin( 2 \pi f t + \theta ) = A\cdot \cos( 2 \pi f t + \theta -\pi/2),\,
where A, f, and \scriptstyle \theta are constant parameters. These functions are periodic with period \scriptstyle T = 1/f, and they are identical except for a displacement of \scriptstyle T/4 along the \scriptstyle t axis. The term phase can refer to several diffe...