🔬 ScienceGrade 4Lesson 20
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Light reflection and refraction
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Learning Objectives
- 1Define reflection and refraction of light
- 2Distinguish between reflection and refraction using real-life examples
- 3Explain how light changes direction when it enters a denser medium
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Mini Lesson
Light travels in straight lines, but its direction can change when it hits a surface or passes from one material into another. The two main ways this happens are reflection and refraction.
Reflection
- Reflection occurs when light bounces off a surface and changes direction.
- The angle of incidence equals the angle of reflection (measured from the normal).
- Smooth, shiny surfaces like mirrors reflect light in a predictable direction (regular reflection).
- Rough surfaces scatter light in many directions (diffuse reflection).
- Examples: mirrors, still water, shiny metal surfaces, moonlight (reflected sunlight).
Refraction
- Refraction occurs when light bends as it passes from one medium into another.
- Light slows down when entering a denser medium (e.g. from air into water) and bends toward the normal.
- Light speeds up when entering a less dense medium and bends away from the normal.
- The amount of bending depends on the difference in density between the two media.
- Examples: a straw appearing bent in water, a rainbow formed by a prism, lenses in eyeglasses.
Key Differences
- Reflection — light bounces back; medium does NOT change.
- Refraction — light passes through; medium CHANGES and light bends.
- Both involve a change in the direction of light travel.
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Tip: remember R-R — Reflection = Ray bounces back (same medium). Refraction = Ray bends as it crosses into a different medium.
Vocabulary
reflection
The bouncing of light off a surface back into the same medium.
refraction
The bending of light as it passes from one medium into another of different density.
normal
An imaginary line perpendicular to a surface at the point where light strikes it.
incident ray
The ray of light that strikes a surface or boundary.
angle of incidence
The angle between the incident ray and the normal.
angle of reflection
The angle between the reflected ray and the normal; equals the angle of incidence.
medium
A material through which light (or another wave) travels, such as air, water, or glass.
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