Question Detail
Question
Two flat mirrors are perpendicular to each other. An incoming beam of light makes an angle of 15° with the surface of the first mirror. As shown in the diagram on page 12, what is the angle of incidence of the reflected beam on the second mirror?
Correct Answer
Option A is the correct answer.
Detailed Explanation
As per the diagram on page 12 (Example 32-1), the initial incident ray makes a 15° angle with the surface of the first mirror. This means its angle of incidence with the normal is 90° - 15° = 75°. By the law of reflection, the reflected ray also makes a 75° angle with the normal (and 15° with the surface of the first mirror). Since the mirrors are perpendicular, this reflected ray then strikes the second mirror. The diagram explicitly labels the angle of incidence on the second mirror (θ3) as 15°. Therefore, the angle of reflection from the second mirror (θ4) will also be 15°.
Hint
Trace the path of the light ray using the Law of Reflection and the geometry of perpendicular mirrors, as shown in the diagram for Example 32-1.