draw ray diagrams to show how a right angled isosceles prism can be used to 
1- deviate the ray through 180 degree 
2- deviate the ray through 90 degree 
3- invert the ray ..

Dear Student,

(1) Deviate the ray through 900 :
Total internal reflection in glass depends on the fact that its critical angle is approximately 420. A light ray with an angle of incidence greater than this will be totally internally reflected. So a light ray with an angle of incidence of 450 will be reflected, and its angle of reflection will also be 450. Hence the light ray is deviated through an angle of 900.

For 900 deviation, a 900 isosceles glass prism is used. In this way the incident ray and the reflected rays are normal to the surfaces they enter and leave. Total internal reflection occurs on the hypotenuse.

(2) Deviate the ray through 1800 :
Besides a 900 deviation, an isosceles prism is also used to produce a 1800 deviation, but this time reflection occurs on the equal, adjacent sides of the prism and not on the hypotenuse.

(3) Invert the ray :
By tracing the above two light rays though the prism, it can be seen that the image produced is inverted. As a result of the image being reflected twice, lateral inversion is cancelled.


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