Let's consider a plane wave of the form $e^{i(\vec{k}.\vec{r}-\omega t)}$ Is the graphical representation the following [![reference : https://fr.wikipedia.org/wiki/Onde_plane][1]][1] or the following ? [![enter image description here][2]][2] I'm wondering what is now the graphical representation for the case of a plane wave of the form $e^{i(k.x-\omega t)}$ ? Is it just that ? [![enter image description here][3]][3] or is it that : [![enter image description here][4]][4] [1]: https://i.sstatic.net/AeuGg.png [2]: https://i.sstatic.net/bwGVl.png [3]: https://i.sstatic.net/3492d.png [4]: https://i.sstatic.net/c465A.png