At a smooth boundary, what is the relationship between the angle of incidence and the angle of reflection?

At a smooth boundary, what is the relationship between the angle of incidence and the angle of reflection?

• A. They Are Supplementary
• B. The Angle of Reflection Is Independent of Incidence
• C. The Angle of Incidence Equals the Angle of Reflection
• D. The Angle of Incidence Is Twice the Angle of Reflection

Answer: (C)

At a smooth boundary, light follows specular reflection: the angle of incidence equals the angle of reflection, with both measured from the surface normal. This symmetry comes from the boundary conditions that conserve the tangential component of the wave’s direction and from the idea that the path of least time is followed, making the incident and reflected rays mirror images across the normal. If the surface were rough, reflection would be diffuse and there wouldn’t be a single equal-angle relation. The other ideas—angles summing to a straight line, being independent of incidence, or being twice as large—don’t describe the predictable mirror-like behavior of a smooth boundary.

At a smooth boundary, light follows specular reflection: the angle of incidence equals the angle of reflection, with both measured from the surface normal. This symmetry comes from the boundary conditions that conserve the tangential component of the wave’s direction and from the idea that the path of least time is followed, making the incident and reflected rays mirror images across the normal. If the surface were rough, reflection would be diffuse and there wouldn’t be a single equal-angle relation. The other ideas—angles summing to a straight line, being independent of incidence, or being twice as large—don’t describe the predictable mirror-like behavior of a smooth boundary.