Question Video: Identifying Examples of Diffuse Reflection | Nagwa Question Video: Identifying Examples of Diffuse Reflection | Nagwa

# Question Video: Identifying Examples of Diffuse Reflection Physics • Second Year of Secondary School

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Which of the following examples of reflection of light rays from a surface shows diffuse reflection? [A] III only [B] IV only [C] II, III, and IV [D] III and IV [E] II and IV

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### Video Transcript

Which of the following examples of reflection of light rays from a surface shows diffuse reflection? (A) III only, (B) IV only, (C) II, III, and IV, (D) III and IV, (E) II and IV.

We have been given four diagrams in which we can see light rays directed at various different surfaces. We are asked to state which of these diagrams shows diffuse reflection.

Let’s recall that we can identify two different categories of reflection: specular reflection and diffuse reflection. Specular reflection occurs when the surface is flat. The normal line, that is, the line perpendicular to the surface, has the same direction at all points on the surface. Diffuse reflection occurs when the surface is uneven. The normal line will have different directions at different points on the surface.

Now, when light reflects off a surface, it does so according to the law of reflection. This law says that the angle of incidence, that is, the angle between the incident ray and the normal, is equal to the angle of reflection; that’s the angle between the reflected ray and the normal.

For specular reflection, no matter where a light ray hits the surface, the normal has the same direction. So, a ray incident at a given angle will be reflected at the same angle, no matter which point on the surface it hits. However, for diffuse reflection, light rays hitting the surface at different positions experience different surface normals. As a result, the reflected rays get scattered in different directions.

When considering whether reflection is specular or diffuse, the direction of the incident rays themselves is irrelevant. All that matters is whether the surface is flat or not. We can see that diagrams I and II show light rays directed at a flat surface. Therefore, these diagrams illustrate specular reflection. Meanwhile, diagrams III and IV show light rays directed at an uneven surface. That means that these diagrams illustrate diffuse reflection.

The correct answer is therefore option (D). The diagrams that show diffuse reflection are III and IV.

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