# Wave and Wave front

#### logearav

Joined Aug 19, 2011
243
Revered members,
What is the difference between wave and wave front?
Geometrically both are represented in the same way. Take for example, my attachment, Here AB is the incident wave front and the perpendiculars drawn to AB at the points A and B that is PA and QC are incident rays.
Do perpendiculars drawn to the top and bottom of the incident wave front qualifies as incident rays?
Similarly in my second attachment PA and QBC are incident rays, while AB is incident wave front.

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#### BillO

Joined Nov 24, 2008
990
The wavefront is just the front of the wave. The line which marks the beginning of the perturbation along the leading edge of the wave.

You can pick any phase of the plane wave as your wave front. As long as all the points are a
t exactly the same phase.. So you track the wave along that plane which represents all those points with a common phase.

It could be a continuous wave, like a sound pressure wave of a long tone, or it could be a pulse of some kind.

You can also define multiple wavefronts as are required to study what ever you need to study. Each wavefront would be at different phase of the wave.

In the case of these examples, they have chosen two wavefronts along the same wave, P and Q, in order to show you how reflection and refraction affect the wave and the wave phase across a plane wave.

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#### logearav

Joined Aug 19, 2011
243
The line which marks the beginning of the perturbation along the leading edge of the wave.
Thanks BillO. In my attachment, which line qualifies for your statement?

#### BillO

Joined Nov 24, 2008
990
They both are. They just represent different phases for the same continuous plane wave. In both examples P arrives first, then Q.

You seem to get caught up in things that are not really important. Mostly in the way things are represented. In this case, they need to show you how a wave behaves when it undergoes reflection and refraction, so they just arbitrarily pick a phase of the wave as P and another as Q. P could be at a peak of the wave, at a zero crossing, or at any other phase of the wave. Q is just another phase, it too could be anywhere along the wave. Just know that it is different than P.

The important thing is, that all the points along P are in phase with each other, as well all, the points along Q are also in phase with each other.