A light ray travels from air into water with an incidence angle of 30°. If n_air ≈ 1.00 and n_water ≈ 1.33, what is the angle of refraction in water approximately?

A light ray travels from air into water with an incidence angle of 30°. If n_air ≈ 1.00 and n_water ≈ 1.33, what is the angle of refraction in water approximately?

• A. About 18°
• B. About 30°
• C. About 36°
• D. About 22°

Answer: (D)

When light moves from air into water, it slows down and bends toward the normal. This bending is described by Snell’s law: n1 sin(theta1) = n2 sin(theta2). With n1 ≈ 1.00, theta1 = 30°, and n2 ≈ 1.33, the angle in water is found from sin(theta2) = (n1/n2) sin(theta1) = (1.00/1.33) * sin(30°) = (1/1.33) * 0.5 ≈ 0.376. The inverse sine gives theta2 ≈ 22°. So the ray refracts at about 22 degrees in water.

When light moves from air into water, it slows down and bends toward the normal. This bending is described by Snell’s law: n1 sin(theta1) = n2 sin(theta2). With n1 ≈ 1.00, theta1 = 30°, and n2 ≈ 1.33, the angle in water is found from sin(theta2) = (n1/n2) sin(theta1) = (1.00/1.33) * sin(30°) = (1/1.33) * 0.5 ≈ 0.376. The inverse sine gives theta2 ≈ 22°. So the ray refracts at about 22 degrees in water.