Reflection Calculator

Reflection Calculator

Critical Angle
Refractive Index1
Refractive Index2


Reflection is a phenomenon of light when light ray bounces off after striking an object.

Laws of Reflection
  • The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane.
  • The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal

Incident ray is the beam of light that strikes the mirror and the reflected ray is the beam of light that bounces off after striking the mirror. Normal is always perpendicular to the surface.

When light crosses an interface into a medium with a higher index of refraction, the light bends towards the normal. Conversely, light traveling across an interface from higher n to lower n will bend away from the normal

Critical angle is the angle at which light travelling from a medium with higher n to a medium with lower n will be refracted at 90°; i.e. refracted along the interface

Total internal reflection – If the light hits the interface at any angle larger than this critical angle, it will not pass through to the second medium at all. Instead, all of it will be reflected back into the first medium


The formula for calculating Critical Angle of reflection is

Sin θc = n2/n1 where n1 > n2


θc Critical Angle
n2 refractive index of medium 2
n1 refractive index of medium 1

Example 1:

A beam of light travels from piece of diamond into water. What is the critical angle of reflection?


Refractive index of Diamond, n1 = 2.42

Refractive index of Water, n2 = 1.33

Sin θc = n2/n1

>Sin θc = 1.33/2.42

θc (Critical Angle) = 33.34°


The standard unit of measurement for Critical Angle is degree.