Q1. A ray of light is incident at an angle of incidence 15° on a plane mirror, as shown in the figure. The value of angle X is:
A 45°
B 65°
C 75° Correct
D 85°
Explanation
The angle of incidence is measured from the normal to the mirror, not from the mirror surface. If the incident ray makes 15° with the normal, then the same geometry leaves 90° - 15° = 75° with the plane mirror surface. Hence angle X, as indicated in the figure, is 75°. The values 45° and 65° do not follow from the complementary angle relation here. The value 85° would correspond to only a 5° angle with the normal, which is not the given incidence angle.