Total Internal Reflection and Critical angle

Physics

result

Experimental verifications of total internal reflection

Experiment 1:
  • Take a glass beaker with clear water in it.
  • Stir the water a few times with a piece of soap, so that it becomes a little turbid.
  • Take a laser pointer and shine its beam through the turbid water.
  • You will find that the path of the beam inside the water shines brightly.
  • Shine the beam from below the beaker such that it strikes at the upper water surface at the other end.
  • It undergoes partial reflection and partial refraction.
  • Now direct the laser beam from one side of the beaker such that it strikes the upper surface of water more obliquely.
  • Adjust the direction of laser beam until you find the angle for which the refraction above the water surface is totally absent.
  • The beam is totally reflected back to water. This is called as total internal reflection.

Experiment 2:
  • Pour the turbid water in a long test tube.
  • Shine the laser light from top.
  • Adjust the direction of the laser beam such that it is totally internally reflected every time it strikes the walls of the tube.
  • This demonstrates total internal reflection.

definition

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.

Definition: 
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.

definition

Total internal reflection (TIR)

Introduction: 
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.

Definition:

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.

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