JAMB Physics 2020 Paper

Concept:Each reflection from a plane mirror turns the ray by twice the angle it makes with the mirror surface.The total deviation is the sum of the deviations produced by the two reflections.Explanation:From the diagram, the first reflection deviates the ray by $2 \times 50^\circ = 100^\circ$.The second reflection deviates the ray by $2 \times 40^\circ = 80^\circ$.So the total deviation is $D = 100^\circ + 80^\circ = 180^\circ$.Therefore, the emergent ray $PQ$ has been turned through $180^\circ$ from the incident ray $NO$.Answer:$180^\circ$ (Option D).