A ray of light originated in air falls perpendicularly on the shorter face of a right angled isosceles(90-45-45) triangular glass prism of refractive index 1.5. Find the angle of deviation in this case in diagram.

According to question a ray of light falls perpendicularly which means angle of incidence = 0. if angle of incidence is 0 then light ray doesn’t refract and moves in a straight line.

if Refractive index of the prism = 1.5 then critical angle is given by
critical angle = arcsin(1/refractive index)
critical angle = arcsin(1/1.5) = 41.81

the figure looks something just like this.

angle of deviaiton for right angled isosceles triangle
angle of deviaiton for right angled isosceles triangle

from figure we know when it hits the larger face , the angle of incidence is 45. since angle of incidence is greater than that of critical angle there is total internal reflection.
total deviation would = 2* glancing angleĀ  in our case glancing angle is 45. so deviation would be 90.


This is Ashish Thapa. It's just a name after all. Just had a thought that our names should signify our situation and should be dynamic. What if our name upgraded with respect to experiences acquired.

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