Figure B.9 shows a 2D cross-section of a snapshot (in time) of the sinusoidal plane wave
for and , with and in the range .
Figure B.10 depicts a more mathematical schematic of a sinusoidal plane wave traveling toward the upper-right of the figure. The dotted lines indicate the crests (peak amplitude location) along the wave.
The direction of travel and spatial frequency are indicated by the vector wavenumber , as discussed in the following section.