When drawing the normal at the point where a light ray strikes a plane mirror
PHYSICS · Single correct · AP · Physics 2: Algebra-based · Geometric Optics · Geometric Optics
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 90∘, 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 (θi=θr).
(d) The normal represents the average orientation of the surface’s microscopic irregularities, so it is taken to be the meaningful reference direction.