A physics student is setting up a demonstration in which a narrow laser beam strikes…
PHYSICS · Multi-part · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction
Problem
A physics student is setting up a demonstration in which a narrow laser beam strikes a flat mirror fixed vertically on an optical bench. The student mistakenly measures the incoming beam’s angle at 30∘ from the mirror surface and predicts that the reflected beam will also leave at 30∘ from the surface.
Answer the following about the student’s procedure and the correct method of determining the outgoing direction of the beam.
(a) Identify the student’s error in the way the angle of incidence is defined. State the correct definition of the angle of incidence for a light ray reflecting from a surface.
(b) Describe a step-by-step procedure for constructing the line against which both the angle of incidence and the angle of reflection must be measured for any point on a reflecting surface.
(c) For an incoming beam that is actually 30∘ below the horizontal and strikes the mirror 60cm above the optical bench, sketch the incident and reflected rays. Clearly label the correct angle of incidence and the correct angle of reflection on your sketch.
(d) Explain qualitatively why measuring the angles relative to the reference line you described in part (b) guarantees that the incident and reflected angles are equal for a perfectly smooth surface.