Hai dao động vuông pha khi:

\[{\rm{\Delta }}\varphi = {\varphi _2} - {\varphi _1} = 2k\pi \]

\[{\rm{\Delta }}\varphi = {\varphi _2} - {\varphi _1} = \left( {2k + 1} \right)\pi \]

\[{\rm{\Delta }}\varphi = {\varphi _2} - {\varphi _1} = \frac{{2k + 1}}{2}\pi \]

\[{\rm{\Delta }}\varphi = {\varphi _2} - {\varphi _1} = \alpha \]bất kì