Explain the Diagramming Waves?

There are two ways that waves can be indicated in a two-dimensional diagram. Parallel lines can be drawn that are meant to show the position of the peak displacement of the waves. This method is most commonly used to show water and sound waves, but it also is used for light, especially when we start talking about interference and diffraction.

Alternatively, rays may be drawn perpendicular to these wavefronts, indicating the direction of travel of the waves. Reflection of waves from a flat surface requires that the angle of incidence, θ_i (measured from the incoming ray to the normal of the reflective surface) must equal the angle of reflection, θ_r (measured from the normal to the reflected ray).