In reflection, what is the relationship between the angle of incidence and the angle of reflection?

In reflection, what is the relationship between the angle of incidence and the angle of reflection?

• A. They are always supplementary.
• B. They are always equal.
• C. They are always perpendicular.
• D. They have no fixed relationship.

Answer: (B)

The key idea is the law of reflection: when light reflects off a smooth surface, the angle it makes with the normal (the line perpendicular to the surface at the point of incidence) is the same on both sides. In other words, the angle of incidence equals the angle of reflection. This symmetry means both rays and the normal all lie in the same plane, and the light path is such that the incoming and outgoing directions are mirror images about the normal. A common pitfall is measuring angles from the surface instead of from the normal; the correct measurement is from the normal, which is why equal angles are observed. For example, if the ray strikes at 30 degrees to the normal, it leaves at 30 degrees to the normal on the other side. The other relationships (supplementary, perpendicular, or no fixed relationship) do not describe how reflection behaves.

The key idea is the law of reflection: when light reflects off a smooth surface, the angle it makes with the normal (the line perpendicular to the surface at the point of incidence) is the same on both sides. In other words, the angle of incidence equals the angle of reflection. This symmetry means both rays and the normal all lie in the same plane, and the light path is such that the incoming and outgoing directions are mirror images about the normal. A common pitfall is measuring angles from the surface instead of from the normal; the correct measurement is from the normal, which is why equal angles are observed. For example, if the ray strikes at 30 degrees to the normal, it leaves at 30 degrees to the normal on the other side. The other relationships (supplementary, perpendicular, or no fixed relationship) do not describe how reflection behaves.