Snell's Law expresses the relationship between the incident and refracted angles and refractive indices as which equation?

• A. n1 sin theta1 = n2 sin theta2
• B. E = h f
• C. v = f lambda
• D. F = m a

Answer: (A)

Light changes speed when it enters a different medium, and that change in speed makes the path bend at the boundary. The relationship that captures this bending is Snell’s Law: n1 sin theta1 = n2 sin theta2. Here theta1 and theta2 are the angles the rays make with the normal to the surface, and n1 and n2 are the refractive indices of the two media. Since n = c/v, a higher n means slower light in that medium, which causes the ray to bend toward the normal when entering a slower medium (n2 > n1) and away from the normal when entering a faster medium (n2 < n1). This equation directly ties the incident and refracted angles to the media’s refractive indices. The other formulas here describe different physics: E = hf pertains to photon energy, v = f lambda to wave speed, and F = ma to force and acceleration.