Physics
Physics
Problem
When drawing the normal at the point where a light ray strikes a plane mirror, which of the following best explains why the normal is drawn perpendicular to the surface? a) The normal shows the direction the light ray would have travelled inside the mirror, so it is used as the comparison line. b) Because measuring the angle to the surface would require subtracting , drawing a perpendicular line gives the angles directly and is therefore more convenient. c) Using a line perpendicular to the surface allows the incident and reflected angles to be measured relative to the same reference, as required by the law of reflection (). d) The normal represents the average orientation of the surface’s microscopic irregularities, so it is taken to be the meaningful reference direction.Intuitive explanation
The normal represents the direction of zero tangential change along the mirror's surface—it's the only direction that's truly "perpendicular" to how the surface is oriented. Since the law of reflection states that angles are measured from this perpendicular, not from the surface itself, the normal becomes the natural reference line. Drawing it perpendicular ensures you're measuring the angle of incidence and reflection correctly, making the geometry of reflection unambiguous and consistent.
Intuitive explanation
The normal represents the direction of zero tangential change along the mirror's surface—it's the only direction that's truly "perpendicular" to how the surface is oriented. Since the law of reflection states that angles are measured from this perpendicular, not from the surface itself, the normal becomes the natural reference line. Drawing it perpendicular ensures you're measuring the angle of incidence and reflection correctly, making the geometry of reflection unambiguous and consistent.