Chapter 9: Light - Reflection and Refraction

Introduction to Light

• Visibility of objects is due to light reflection and transmission.
• Common phenomena: image formation by mirrors, star twinkling, rainbows, bending of light.
• Light travels in straight lines, forming sharp shadows.
• Diffraction occurs when light bends around small objects, indicating its wave nature.
• Quantum theory reconciles light's wave and particle properties.

Reflection of Light

• Laws of Reflection:
  1. Angle of incidence = Angle of reflection
  2. Incident ray, normal, and reflected ray lie in the same plane.
• Plane mirror images are virtual, erect, and laterally inverted.

Spherical Mirrors

• Types:
  • Concave: Inward reflecting surface.
  • Convex: Outward reflecting surface.
• Important terms:
  • Pole (P): Center of the mirror surface.
  • Centre of Curvature (C): Center of the sphere from which the mirror segment is taken.
  • Radius of Curvature (R): Distance PC.
  • Principal Axis: Line through P and C.
  • Principal Focus (F): Point where parallel rays converge or appear to diverge.

Image Formation by Spherical Mirrors

• Activity to explore image size and nature based on object position relative to P, F, and C.
• Ray Diagrams: Use two specific rays to determine image location:
  1. Parallel to principal axis reflects through F (concave) or appears from F (convex).
  2. Through F reflects parallel to principal axis.
  3. Through C reflects back on itself.
  4. Incident obliquely reflects obliquely.

Mirror Formula and Magnification

• Formula: ( \frac{1}{v} + \frac{1}{u} = \frac{1}{f} )
• Magnification ( m = \frac{\text{height of image}}{\text{height of object}} )
• Sign conventions based on New Cartesian System.

Refraction of Light

• Light changes direction when moving between different media (refraction).
• Laws of Refraction:
  1. Incident ray, refracted ray, and normal lie in the same plane.
  2. ( \frac{\sin i}{\sin r} = \text{constant} ) (Snell's Law)

Refractive Index

• Ratio of speed of light in two media: ( n_{21} = \frac{v_1}{v_2} )
• Absolute refractive index ( n = \frac{c}{v} )
• Optical density relates to refractive index not mass density._

Refraction by Spherical Lenses

• Types:
  • Convex: Converging lens
  • Concave: Diverging lens
• Terms:
  • Principal Axis
  • Optical Centre (O)
  • Principal Focus (F1, F2)

Image Formation by Lenses

• Lens Formula: Similar to mirrors, ( \frac{1}{v} - \frac{1}{u} = \frac{1}{f} )
• Magnification ( m = \frac{v}{u} = \frac{h^{'}}{h} )
• Sign conventions similar to mirrors.

Power of a Lens

• Power ( P = \frac{1}{f} ), measured in dioptres.
• Lens combinations: sum of individual powers.

Practical Applications

• Uses of concave and convex mirrors and lenses in everyday objects.
• Activities and experiments illustrate principles.

Conclusion

• Review of light's properties, laws of reflection and refraction, and how mirrors and lenses form images.

Exercises

• Review questions to test understanding of reflection, refraction, and lens/mirror concepts.