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Snell's law of refraction at the boundary between two media of refractive indices $n_1$ and $n_2$ states
A$n_1\sin\theta_1 = n_2\sin\theta_2$
B$n_1\cos\theta_1 = n_2\cos\theta_2$
C$n_1\tan\theta_1 = n_2\tan\theta_2$
D$n_1 + \theta_1 = n_2 + \theta_2$
Answer & Solution
Correct answer: A. $n_1\sin\theta_1 = n_2\sin\theta_2$
1. NCERT §9.3 (Refraction): when a ray crosses from medium 1 to medium 2, the angles of incidence and refraction (both measured from the NORMAL) satisfy $n_1\sin\theta_1 = n_2\sin\theta_2$.
2. Consequence: when light enters a denser medium (higher $n$), it bends TOWARD the normal; entering rarer (lower $n$), it bends AWAY.
3. The refractive index $n = c/v$ measures how much slower light travels in the medium.
4. Options B, C, D have wrong trigonometric functions or wrong functional form — Snell's law has no derivation that produces cosines, tangents, or sums.
_Source: NCERT Class 12 Physics Part 2, Ch 9 "Ray Optics", §9.3 (Refraction, Eq. 9.4), p. 2–3._
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