---
title: "A narrow parallel beam of light traveling through air strikes a flat but unpolished, microscopically rough surface, resulting in diffuse reflection as shown in the diagram. Which of the following claims correctly compares the angle of incidence to the angle of reflection for an individual ray in the beam, and provides a correct physical justification for why the reflected light scatters in multiple directions?"
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url: "https://nerd-notes.com/ubq/117392/"
date_modified: "2026-08-04T06:52:03+00:00"
---

# A narrow parallel beam of light traveling through air strikes a flat but unpolished, microscopically rough surface, resulting in diffuse reflection as shown in the diagram. Which of the following claims correctly compares the angle of incidence to the angle of reflection for an individual ray in the beam, and provides a correct physical justification for why the reflected light scatters in multiple directions?

A narrow parallel beam of light traveling through air strikes a flat but unpolished, microscopically rough surface, resulting in diffuse reflection as shown in the diagram. Which of the following claims correctly compares the angle of incidence to the angle of reflection for an individual ray in the beam, and provides a correct physical justification for why the reflected light scatters in multiple directions?

![A 2D schematic diagram showing three parallel incident rays of light striking a horizontal, microscopically rough surface from the upper-left. The surface baseline is horizontal, but the top boundary of the surface has small irregular jagged peaks and valleys. Three parallel incoming light rays, represented by straight solid lines with arrows pointing downward and to the right, strike three different points on the jagged surface. At each of the three impact points, a short dashed line represents the local surface normal perpendicular to the surface tangent at that specific point. Three reflected light rays, represented by solid lines with arrows pointing away from the surface, emerge from the impact points in three different directions. For each ray, the angle between the incident ray and the dashed local normal is equal to the angle between the reflected ray and the same dashed local normal. Labels \(\theta_i\) and \(\theta_r\) appear at one of the contact points between the ray and the dashed normal line. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1785826322-TKWAis.jpg)

- **A.** The angle of incidence does not equal the angle of reflection for individual light rays, because the law of reflection applies only to smooth surfaces.
- **B.** The angle of incidence equals the angle of reflection for each individual light ray, because the law of reflection holds locally relative to the local surface normal at each point of contact.
- **C.** The angle of incidence equals the angle of reflection for each individual light ray, because all rays in the beam share the same surface normal relative to the macroscopic flat plane.
- **D.** The angle of incidence is greater than the angle of reflection for individual light rays, because the roughness of the surface absorbs energy from the rays upon impact.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/117392/*