For coherent sources that are initially in phase, constructive interference occurs when the path difference is a whole number of wavelengths, while destructive interference occurs at an odd number of half-wavelengths. This is IB Physics C.3 Wave phenomena for both SL and HL.
Interference follows the principle of superposition: when waves overlap, their individual displacements add algebraically to give the resultant displacement. A stable pattern requires coherent sources, which have the same frequency and a constant phase difference.
| Interference | Path-difference condition | Phase-difference condition |
|---|---|---|
| Constructive |