A ray of light passes from a medium with refractive index 1.50 into a medium with refractive index 1.20. If the angle of incidence is 40°, what is the angle of refraction? (Use sin 40° = 0.643 and arcsin(0.804) = 53.5°)
Show the answer and explanation
Correct answer
C. 53.5°
Principle or equation
Snell's law: n1 sin θ1 = n2 sin θ2. Solve for θ2 = arcsin( (n1/n2) sin θ1 ).
Why this answer is correct
n1 = 1.50, θ1 = 40°, n2 = 1.20. sin θ2 = (1.50/1.20) × sin 40° = 1.25 × 0.643 = 0.80375 ≈ 0.804. θ2 = arcsin(0.804) = 53.5°.
Example
If light goes from n=1.5 to n=1.0 with incidence 30°, sin θ2 = 1.5 × 0.5 = 0.75, θ2 ≈ 48.6°.
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