There is a very simple relationship between the phase and path difference.

A whole wavelength corresponds to one whole oscillation, a path difference ofThis is turn corresponds to a phase difference ofor 360 °. Confusion arises because many waves are sinusoidal so the displacement from equilibrium is given bywhereso whenincreases byincreases by

The angle however may also be measured in degrees so a phase difference of %pi means the same as a phase difference of 180°, and both of these are equivalent to a path difference of

The following table shows equivalent path and phase difference for different phase/path differences.

Path difference |
Phase Difference in Degrees |
Phase Difference in Radians |

0 |
0° |
0 |

45° |
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90° |
||

135° |
||

180° |
||

225° |
||

270° |
||

315° |
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360° |