A light ray travels from glass (n1 = 1.50) into air (n2 = 1.00) with an incidence angle of 40° relative to the normal. What is the refracted angle in air?

A light ray travels from glass (n1 = 1.50) into air (n2 = 1.00) with an incidence angle of 40° relative to the normal. What is the refracted angle in air?

• A. About 45.0°
• B. About 74.8°
• C. About 60.0°
• D. About 30.0°

Answer: (B)

This question tests how light bends at a boundary using Snell's law: n1 sin θ1 = n2 sin θ2. With light going from glass (n1 = 1.50) to air (n2 = 1.00) and an incidence angle of 40°, compute sin θ2 = (n1/n2) sin θ1 = 1.50 × sin 40° ≈ 1.50 × 0.6428 ≈ 0.9642. Then θ2 ≈ arcsin(0.9642) ≈ 74.8°. Since moving from a denser to a rarer medium, the refracted ray makes a larger angle with the normal, so it bends away from the normal. The value is well below 90°, so refraction occurs rather than total internal reflection.

This question tests how light bends at a boundary using Snell's law: n1 sin θ1 = n2 sin θ2. With light going from glass (n1 = 1.50) to air (n2 = 1.00) and an incidence angle of 40°, compute sin θ2 = (n1/n2) sin θ1 = 1.50 × sin 40° ≈ 1.50 × 0.6428 ≈ 0.9642. Then θ2 ≈ arcsin(0.9642) ≈ 74.8°. Since moving from a denser to a rarer medium, the refracted ray makes a larger angle with the normal, so it bends away from the normal. The value is well below 90°, so refraction occurs rather than total internal reflection.