- The angle of refraction is measured between the refracted ray of light and the normal.
- The normal is an imaginary line drawn on a ray-tracing diagram perpendicular to the surface at the point of incidence.
- Expressed more formally, in optics, the normal is a geometric construct, a line drawn perpendicular to the interface between two media at the point of contact. This conceptually defined reference line is crucial for characterizing various light-matter interactions, such as reflection, refraction, and absorption.
- The equation used to determine the angle of refraction is often referred to as Snell’s law or the law of refraction.
- The law of refraction describes the relationship between the angle of incidence and the angle of refraction when light crosses the boundary between two transparent media, such as from air to water.
- In the field of optics, Snell’s law is applied when drawing a ray-tracing diagram to calculate the angles of incidence and refraction and is also used experimentally to determine the refractive index of a given medium.

- The refractive index of a medium can significantly affect the degree to which light is refracted when entering that medium.
- For instance, light is refracted more when it enters a medium with a high refractive index, such as glass, than when it enters a medium with a low refractive index, like air.
- Total internal reflection is a phenomenon that takes place when light attempts to pass from a medium with a higher refractive index to one with a lower refractive index at an angle greater than the so-called “critical angle”. The outcome is that all of the light is reflected back into the first medium instead of being refracted.

###### About lines that are normal to one another

- If one line is normal to another, then it is at right angles.
- In geometry, a normal (or
*the*normal) refers to a line drawn perpendicular to and intersecting another line, plane or surface. - In the field of optics, the normal is a line drawn on a ray-tracing diagram perpendicular to (at 90
^{0}to), the boundary between two media. - If the boundary between two media is curved then the normal is drawn at a tangent to the boundary.

###### References

The angle of refraction measures the angle to which light bends as it passes across the boundary between different media.

- The angle of refraction is measured between a ray of light and an imaginary line called the
*normal*. - In optics, the
*normal*is a line drawn on a ray diagram perpendicular to, so at a right angle to (90^{0}), the boundary between two media. - See this diagram for an explanation: Refraction of a ray of light
- If the boundary between the media is curved, the
*normal*is drawn perpendicular to the boundary.