A light ray in air (n = 1.00) strikes a flat surface of a transparent material at an angle of incidence of 60°. The angle of refraction in the material is 35°. What is the refractive index of the material? (Use sin 60° = 0.866 and sin 35° = 0.574.)
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Correct answer
C. 1.51
Principle or equation
Snell's law: n1 sin θ1 = n2 sin θ2, where n1 and n2 are the refractive indices of the two media, and θ1 and θ2 are the angles of incidence and refraction, respectively.
Why this answer is correct
Here n1 = 1.00, θ1 = 60°, θ2 = 35°. So n2 = n1 sin θ1 / sin θ2 = (1.00 × 0.866) / 0.574 ≈ 1.51.
Example
If a ray goes from air into a medium with n = 1.50 at an incidence angle of 45°, the angle of refraction is about 28.1°.
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