## Phase and Path Difference

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° 90° 135° 180° 225° 270° 315° 360°