Reflection and refraction
Posted in Physics, OpticsReflection
Reflection is where light changes direction when it reaches a border between two different materials. The light is reflected back at the same angle it enters as measured in relation to the normal, a line perpendicular to the boundary of the two mediums.
The angle between the normal (dashed line) and the incoming light, r, is the same as the angle between the normal and reflected light.
Refraction
When light travels from one material to another it changes speed and therefore direction. The angle between the refracted light and the normal is called 'angle of incidence' and is given the letter i.
The refractive index describes how much light will be refracted (or slowed down) in a material compared with the speed of light in a vacuum. Hence the equation for the refractive index, n, of a material is given by:
Where c is the speed of light in a vacuum and v is the speed of light in the material.
Snell's law
Snell's law related the angle of the incoming/reflected light, r, and the angle of the refracted light, i:
Total internal reflection
Total internal reflection occurs when no light is refracted, that is the light stays inside a material. The smallest angle of reflection (r, above) at which light is totally internally reflected, in a given material, is called the critical angle and is given by the equation: