Lecture on Reflection of Light

Introduction to Reflection

• Reflection: Bouncing back of light rays when they strike a polished surface.
• Practical example: Seeing your face in a mirror.
• Types of Reflection: Regular and Irregular (diffuse).

Characteristics of Regular Reflection

• Occurs on smooth surfaces like mirrors or stainless steel plates.
• Incident Ray: Ray striking the surface.
• Reflected Ray: Ray bouncing back from the surface.
• Angle of Incidence (i): Angle between incident ray and the normal.
• Angle of Reflection (r): Angle between reflected ray and normal.
• Law: Angle of Incidence (i) = Angle of Reflection (r).

Irregular Reflection

• Occurs on rough surfaces like walls or notebooks.
• Light rays are scattered in different directions.

Key Terms in Reflection

• Point of Incidence: Point where incident ray strikes the surface.
• Normal: Perpendicular line to the surface at the point of incidence.
• Plane Mirror: Mirror with a flat reflective surface.
• Real Images: Formed by actual intersection of reflected rays; can be captured on a screen.
• Virtual Images: Formed by apparent divergence of reflected rays; cannot be captured on a screen.

Formation of Images by Plane Mirrors

• Real Images: Always inverted.
• Virtual Images: Always upright and formed in mirrors.
• Equal distance: Object distance from mirror = Image distance behind mirror.
• Lateral Inversion: Exchange of left and right in the image.
• Number of Images: With inclined mirrors, related by the formula (360°/θ - 1).

Spherical Mirrors

• Concave Mirrors: Reflective surface is inward, resembling a spoon's inner surface.
  • Real and inverted images formed at focus.
• Convex Mirrors: Reflective surface is outward, resembling a spoon's outer surface.
  • Always forms virtual, upright, and diminished images.

Key Points for Spherical Mirrors

• Center of Curvature: Center of the sphere from which mirror is a part.
• Radius of Curvature: Distance between the pole and the center of curvature.
• Principal Axis: Line joining the pole and center of curvature.
• Principal Focus: Point where parallel rays converge (concave) or appear to diverge (convex).
• Focal Length (f): Distance between the pole and the principal focus.

Practical Uses of Mirrors

• Concave Mirrors: Used in torches, headlights as they focus light beams.
• Convex Mirrors: Used in vehicle side mirrors, streetlights for a wider field of view.

Summary

• Regular vs Irregular Reflection: Smooth vs rough surfaces.
• Laws of Reflection: Angle of incidence equals angle of reflection.
• Image Formation: Real vs virtual images; usage in various applications.
• Mirrors: Types, uses, and key properties.