The angle between the reflected beam and the line perpendicular to the boundary is called the

• A. Angle of incidence
• B. Angle of reflection
• C. Angle of refraction
• D. Angle of deviation

Answer: (B)

The key idea is how we measure angles in reflection using the normal to the boundary. The line perpendicular to the boundary is the normal, and the angle formed between the reflected ray and that normal is defined as the angle of reflection. This mirrors how we define the angle of incidence—the angle between the incoming ray and the same normal. The law of reflection states these two angles are equal, which is why this particular angle is given its name.

The other terms don’t fit this specific definition: the angle of incidence refers to the incoming ray’s angle with the normal; the angle of refraction is about the bending of the ray as it passes into a new medium and is measured from the normal in that new medium; the angle of deviation describes how far the overall path has changed direction, often between the incident and emergent rays.