A ray of light passes from water (n = 1.33) into a transparent solid. The angle of incidence in water is 40°, and the angle of refraction in the solid is 25°. What is the refractive index of the solid? (Use sin 40° = 0.643 and sin 25° = 0.423)
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Correct answer
C. 2.02
Principle or equation
Snell's law: n1 sin θ1 = n2 sin θ2.
Why this answer is correct
Apply Snell's law: 1.33 × sin 40° = n2 × sin 25°. Thus n2 = (1.33 × 0.643) / 0.423 ≈ 2.02.
Example
If light goes from air (n=1) into glass at 30° and refracts at 19.5°, then n_glass = sin30/sin19.5 ≈ 1.5.
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