37. Reflection

GCSE Physics: Reflection

1. What Happens at a Boundary?

When a wave hits the boundary between two different materials, three things can happen:

• Absorption: The wave's energy is transferred to the material's energy stores.

• Transmission: The wave passes through the material (often leading to refraction).

• Reflection: The wave "bounces" off the surface and never enters the material.

2. The Law of Reflection

The most important rule to remember for reflection is:The angle of incidence is always equal to the angle of reflection.

3. Drawing Ray Diagrams

To show reflection, we use ray diagrams. Here are the components you need to include:

• The Boundary: The surface where the reflection occurs (e.g., a mirror).

• Incoming Ray: The light ray moving towards the boundary (add an arrow for direction).

• The Normal: A dashed line drawn at 90 degrees (perpendicular) to the surface at the point where the ray hits.

• Angle of Incidence ($i$): The angle between the incoming ray and the normal.

• Point of Incidence: The exact spot where the incoming ray touches the boundary.

• Reflected Ray: The ray bouncing away from the surface.

• Angle of Reflection ($r$): The angle between the reflected ray and the normal (this must equal the angle of incidence).

4. Types of Reflection

Specular Reflection

• Surface: Perfectly smooth and flat (e.g., a mirror).

• Effect: All normals point in the same direction, so all light rays reflect in the same direction.

• Result: Provides a clear, sharp image.

Diffuse (Scattered) Reflection

• Surface: Rough or "bumpy" when viewed closely (e.g., a piece of paper).

• Effect: Because the surface is uneven, the normals point in many different directions.

• Result: Light rays are reflected (scattered) in all different directions, which is why you cannot see a clear reflection in paper.

• Note: The law of reflection still applies to every single tiny bump on the surface!

5. Summary Table