Snell's Law for refraction at air-water interface

Steps:

• Apply Snell's Law: n₁ sin i = n₂ sin r, where n₁ (air) = 1, n₂ (water) = 1.3, r = 40°.
• Rearrange for i: sin i = (n₂ / n₁) sin r = 1.3 × sin 40°.
• Calculate sin 40° ≈ 0.6428, so sin i ≈ 1.3 × 0.6428 = 0.8356.
• i = arcsin(0.8356) ≈ 57°.

Why D is correct:

• Snell's Law precisely calculates the incident angle as 57° using n sin i = n' sin r.

Why the others are wrong:

• A: 30° violates Snell's Law, as it underestimates incidence for given refraction.
• B: 50° is too low, ignoring the full refractive index effect.
• C: 52° approximates but falls short of the exact arcsin result.

Final answer: D