NEETPhysicsRay Optics
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): When a light ray is incident normally on the vertical face of a thin right-angled prism of refractive index and prism angle A , the angle of emergence is A . Reason (R): The ray passes undeviated through the first face, making the angle of incidence at the second face equal to zero. In the light of
Options
- ABoth (A) and (R) are correct and (R) is the correct explanation of (A)
- BBoth (A) and (R) are correct but (R) is not the correct explanation of (A)
- C(A) is correct but (R) is not correct
- DBoth (A) and (R) are not correct
Correct answer
C. (A) is correct but (R) is not correct
Step-by-step solution
Assertion (A) is correct: When a ray is incident normally on the first face, the angle of incidence i = 0^ , so the angle of refraction at the first face r₁ = 0^ . For a prism, the internal angles are related by r₁ + r₂ = A , which gives the angle of incidence at the second face r₂ = A . Using Snell's law for small angles at the second face ( e = r₂ ), the angle of emergence is e = A . Reason (R) is incorrect: While it is true that the ray passes undeviated through the first face, this geometry makes the angle of i