Two plane mirrors are hinged along one edge so that they form a movable "V" shape
PHYSICS · Multi-part · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction
Problem
Two plane mirrors are hinged along one edge so that they form a movable "V" shape. The mirrors make an angle of 60° with one another. A narrow laser beam in air lies in the plane that contains both mirror surfaces and strikes Mirror 1 at a point 8.0 cm from the hinge. At the point of impact the beam makes an angle of 20° with the normal to Mirror 1.
A sheet of paper is placed beneath the mirrors so students can trace the path of the ray.
Answer the following in the spaces provided.
(a) Draw a clearly labeled ray diagram that shows the path of the beam from the moment it strikes Mirror 1 until it leaves Mirror 2 after the second reflection. Indicate all normal lines and all relevant angles.
(b) Using the law of reflection and appropriate angle relationships, explain why the total angle through which the beam is turned (the angle between the incident and final directions) equals twice the angle between the mirrors.
(c) Describe qualitatively how the total turning angle would change if the mirrors were opened to 90° while keeping the incident angle of 20° the same. Provide reasoning based on your diagram.
(d) Specular reflection is assumed in the analysis above. Explain how the outcome would differ if the mirror surfaces were rough enough to cause diffuse reflection.