TIR And Critical Angle


Factors affecting critical angle

Critical angle is affected by the refractive index of second medium with respect to the first medium. This in turn depends on:
  • Wavelength: Critical angle increases with increase in wavelength (least for violet).
  • Temperature: Critical angle increases with increase in temperature. 


Critical angle

When the angle of incidence in water reaches a certain critical value, the refracted ray lies along the boundary, having an angle of refraction of 90-degrees. This angle of incidence is known as the critical angle; it is the largest angle of incidence for which refraction can still occur. For any angle of incidence greater than the critical angle, light will undergo total internal reflection.

The angle of incidence beyond which rays of light passing through a denser medium to the surface of a less dense medium are no longer refracted but totally reflected.


Total internal reflection (TIR)

When light travels from an optically denser medium to a rarer medium at the interface, it is partly reflected back into the same medium and partly refracted to the second medium. This reflection is called the internal reflection.


Total internal reflection is defined as the complete reflection of a light ray at the boundary of two media, when the ray is in the medium with greater refractive index.


Relation between refractive index and critical angle

Let us consider medium 1 Incident medium and 2 Refractive medium, Then value of critical angle can be derived by Snell's law.

: Refractive index of denser medium 1 with respect to rarer medium 2.