JEE MainPhysicsGeometrical OpticsMCQ+4 / −1
Monochromatic light is incident on a glass prism of angle . If the refractive index of the material of the prism is , a ray, incident at an angle . on the face would get transmitted through the face of the prism provided : 

- A
- B
- C
- D
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Correct answer: C
- Refraction at first face
Let the angle of incidence on face be , and the angle of refraction inside the prism at face be .
By Snell's law: so,
- Condition at second face
Let the angle of incidence at the second face inside the prism be . For a prism, Hence,
For the ray to emerge from face , it must not suffer total internal reflection. Thus, where the critical angle for glass-air interface is
Therefore,
This gives
- Convert this into condition on
Using we get
Hence,
So the ray will be transmitted through face provided is greater than this limiting value.
Thus the matching option is:
- Check options
- A and B involve , which does not arise here.
- D has the wrong inequality sign.
- C matches the derived result.
Therefore, the correct option is C.
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