Phase difference is a concept that primarily applies to coherent waves. Coherence refers to a property of waves where they have a constant phase relationship or a fixed phase difference between them. In coherent waves, the phase difference remains constant over time.
When two or more waves are coherent, their waveforms align and can interfere constructively or destructively. The phase difference between them determines how they combine at different points in space and time.
For example, in the case of two coherent waves, if their peaks and troughs align perfectly, they are said to be in phase, and they will reinforce each other, resulting in constructive interference. Conversely, if their peaks align with the troughs of the other wave, they are said to be in phase opposition or out of phase, and they will cancel each other out, resulting in destructive interference.
However, for incoherent or non-coherent waves, the phase relationship between them is not fixed or predictable. In such cases, the waves do not maintain a constant phase difference, and their interference patterns become random or averaged out over time.
It's important to note that coherence is not an all-or-nothing property. Waves can have varying degrees of coherence. For example, partially coherent waves have a partial correlation in their phases, while fully coherent waves have a precise and consistent phase relationship.
In summary, while phase difference is a key concept in understanding the interference of coherent waves, it does not have a well-defined meaning or significance for incoherent waves.