Which law describes the refraction of light at an interface between media of different refractive indices?

• A. Snell's Law n1 sin theta1 = n2 sin theta2
• B. Ohm's Law
• C. Newton's second law
• D. Coulomb's Law

Answer: (A)

When light crosses a boundary between media with different refractive indices, its speed changes and the path bends. The relationship that ties the incident and refracted angles to the material properties is Snell's law: n1 sin theta1 = n2 sin theta2. The refractive index n of a medium is c divided by the light’s speed in that medium, so this equation reflects how the speed change governs the bending of the beam. If the second medium is denser (n2 > n1), the light slows and bends toward the normal; if it’s less dense (n2 < n1), it speeds up and bends away from the normal. The other laws mentioned describe unrelated effects: Ohm's law for electric circuits, Newton's second law for forces on mass, and Coulomb's law for electrostatic forces.