Final answer:
The Law of Reflection in Physics states that the angle of reflection must be equal to the angle of incidence, which is mathematically expressed as θ1 = θr, with both angles measured relative to the perpendicular to the surface at the point of contact.
Step-by-step explanation:
The Law of Reflection in Physics stipulates that the angle of reflection is always equal to the angle of incidence, which is represented mathematically as θ1 = θr (where θ1 is the angle of incidence and θr is the angle of reflection). These angles are measured in relation to the normal line, which is perpendicular to the surface at the point of incidence. This principle applies to smooth surfaces such as mirrors, where the reflection of light occurs at specific angles, resulting in a clear image. Conversely, rough surfaces disperse light in many directions, leading to diffuse reflection.
An example of this phenomenon occurs when you look into a flat mirror; the light bouncing back from it follows the law of reflection, allowing you to see your reflection. On the multiple-choice question provided, the correct answer is "D. must be equal to the angle of reflection" based on the information given that the angle of reflection equals the angle of incidence (θ1 = θr).