In an experiment demonstrating the laws of reflection, if the plane containing the reflected ray is disrupted (e.g., by bending the paper), the ray…

Correct Option

The correct option is

The incident ray, reflected ray, and normal must lie in the same plane.

Explanation

The reflection of light is governed by two fundamental laws. The first law states that the angle of incidence is equal to the angle of reflection. The second law defines the spatial relationship between the light rays and the surface normal.

Analysis

The experiment described is a standard demonstration used to verify the second law of reflection.

• Statement The incident ray, reflected ray, and normal must lie in the same plane. is Correct: The second law of reflection states that the incident ray, the normal to the surface at the point of incidence, and the reflected ray all lie in the same plane. In the experiment, the sheet of paper represents this plane. As long as the paper is flat, the reflected ray travels along it and is visible. When the paper is bent or folded, that portion of the paper is moved out of the plane defined by the incident ray and the normal. Since the reflected ray continues to travel in the original plane, it does not strike the bent part of the paper, making it appear invisible on that surface.
• Statement Light is absorbed by non-planar surfaces. is Incorrect: The invisibility of the ray is due to the geometric alignment of the paper relative to the path of light, not because the surface absorbs the light.
• Statement The angle of reflection varies with the surface curvature. is Incorrect: While surface curvature affects the direction of reflection, the specific phenomenon of the ray disappearing from the paper when bent is a test of coplanarity, not the relationship between angle and curvature.
• Statement The intensity of light decreases below the visual threshold. is Incorrect: The light intensity remains sufficient for visibility; the ray simply does not intersect with the physical surface of the paper once the plane is disrupted.

Key Takeaway: The incident ray, the reflected ray, and the normal at the point of incidence are coplanar; they must always exist within the same geometric plane.