---
title: 'The 5 laws of geometrical optics'
media_order: 'interaction_lumiere_surface_3.gif,Opt_Geo_refle_lim.gif,Loi_reflexion.png,Opt_Geo_loi_refrac.jpg'
---

###The 5 laws of light rays optics

**Fermat's principle $\Longrightarrow$ 5 las of light rays optics**


##### Propagation of light is rectilinear

In an homogenous and isotropice medium for its optical properties, light rays propagate in straight lines.

##### Light rays do not interact with each other


##### Law of reflection

<!--Comment for a fursther step :
Rays are geometrical constructions that indicate the direction of flow of the luminous energy
- in an homogenous medium, rays are stright lines.
- in an isotropic medium, rays
-->

* The **reflected ray** *belongs to the incidente plane*, and is*located in the opposite side to that of the incident ray*, with regard to the normal of the surface at the impact point. **The angle of reflection $r$ is equal to the angle of incidence $i_1$ :

$r=i_1$**

![](Loi_reflexion.png)

##### Law of refraction

![](Opt_Geo_loi_refrac.jpg)

[](https://www.geogebra.org/material/iframe/id/bg5ewxee)



