# Wavefront and wave radius

Let’s imagine that we are on the edge of a lake. At any given moment, we throw a stone on the surface of the water. It is possible to see that the point reached will be *disturbed* . Therefore, on the surface of the lake, we will see the formation of concentric circles whose radii increase over time. When this disturbance propagates, we say that it constitutes a *wave* . Thus, we can define a wave as follows:

*A wave is the propagation of energy from one point to another, without any transport of matter between them.*

To schematically represent the propagation of waves, we use two simple tricks:

**Wavefront**is the region of space that gathers all the points in the middle reached simultaneously by a pulse (we say that all points of a wavefront have the same phase). Wavefronts can be called*wave surfaces*.**A wave ray**is an oriented line that originates at the wave source and is perpendicular to the wavefronts, drawn to indicate the direction of wave propagation at each point in the medium. Let’s see the figure below:

As for the wave propagation , that is, as for the relevant wave direction, we say that there are three types of waves: one-dimensional, two-dimensional and three-dimensional .

**One- dimensional** is the wave that propagates in a single dimension, like waves on tensioned strings.

**Two- dimensional** is the wave that propagates in two directions, that is, in a plane, for example, waves on surfaces of liquids.

**Three- dimensional** is the wave that propagates in three dimensions, that is, in space, as most light waves and sound waves do.