Before revision: Such directions of energy flow, which are always perpendicular to the wavefront, are called rays creating multiple wavefronts.University Physics – With Modern Physics (12th Edition), H. D. Young, R. A. Freedman (Original edition), Addison-Wesley (Pearson International), 1st Edition: 1949, 12th Edition: 2008, , The simplest form of a wavefront is the plane wave, where the rays are parallel to one another.
After revision: 200px|Rays and wavefrontsSuch directions of energy flow, which are always perpendicular to the wavefront, are called rays creating multiple wavefronts.University Physics – With Modern Physics (12th Edition), H. D. Young, R. A. Freedman (Original edition), Addison-Wesley (Pearson International), 1st Edition: 1949, 12th Edition: 2008, , The simplest form of a wavefront is the plane wave, where the rays are parallel to one another.