# Problems on Tir in Prism

Physics

## example

### Total internal reflection in a Prism

Example: A ray monochromatic light is incident on the face of prism near vertex at an incident angle of (see figure). If the refractive index of the material of the prism is , then find the angle between incident and emergent ray.

Solution:
Ray OP goes parallel to the side BC. Hence the angle of incidence of this ray on the side CD becomes .Applying Snell's Law at the point Q,Hence, this is a case of total internal reflection.Thus the angle of incidence on Q is equal to the angle of reflection.This forms as angle of incidence on side AD.By Snell's Law,Thus the angle between rays OP and RS is .

## example

### Problem on TIR in prism

Problem:
A ray of light is incident normally on one face of a prism as shown in figure. The refractive index of the material of the prism is  and the prism is immersed in water of refractive index  then find angle of emergence and point of TIR.

Solution:
Initially at P, there is TIR, There force at Q (snells law)

If

Therefore, now TIR will not occur at P

## example

### Application of total internal reflection in a prism.

Many optical instruments use right -angled prisms to reflect a beam of light through or (By total internal reflection) such as cameras, binoculars, periscope and telescope.

When a ray of light strikes a face of prism perpendicular, it enters the prism without deviation and strikes the hypotenuse at an angle of . Since the angle of incidence is greater than critical angle of the glass which is , the light is totally reflected by the prism through an angle of . Two such prisms are used in periscope. The  light is totally reflected by the prism by an angle of . Two such prisms are used in binoculars.

Prism is also used to invert images without changing their size.