25.2 The Law of Reflection

Light reflection is a fundamental concept in optics. It explains how light bounces off surfaces, creating images we see daily. Understanding reflection helps us grasp how mirrors work and why objects appear the way they do.

The law of reflection states that the angle of incidence equals the angle of reflection. This principle applies to both smooth and rough surfaces, affecting how light is scattered. It's crucial for understanding image formation in mirrors and other reflective objects.

The Law of Reflection

Reflection from surface types

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• Smooth surfaces
  • Reflect light uniformly and predictably
  • Incident rays hitting at the same angle will reflect at the same angle (specular reflection)
  • Examples: plane mirrors, polished metal, still water
• Rough surfaces
  • Reflect light in various directions due to irregular surface
  • Incident rays hitting at the same angle will reflect at different angles (diffuse reflection)
  • Examples: paper, matte paint, unpolished wood

Wave Optics and Reflection

• Light rays are part of the electromagnetic spectrum
• Reflection occurs when light waves bounce off a surface
• The law of reflection applies to both particle and wave models of light

Calculations with reflection law

• Law of reflection states angle of incidence equals angle of reflection
  • [object Object],[object Object]
  • $\theta_i$ is angle of incidence, measured between incident ray and normal
  • $\theta_r$ is angle of reflection, measured between reflected ray and normal
• Normal is imaginary line perpendicular to surface at point of incidence
• To calculate angle of reflection, measure angle of incidence and use law of reflection
• To calculate angle of incidence, measure angle of reflection and use law of reflection
• The incident ray, reflected ray, and normal all lie in the same plane

Formation of mirror images

• Mirror images formed by reflection of light from mirror's surface
• Image appears behind mirror because brain interprets light as coming from point behind mirror
  • Due to way reflected light rays converge and appear to originate from behind mirror
• Distance between object and mirror equals apparent distance between image and mirror
  • Explains why image appears same size as object
• Characteristics of mirror images
  • Virtual: cannot be projected onto a screen
  • Upright: not inverted
  • Laterally inverted: left and right sides are swapped