Light – Reflection and Refraction

• Introduction to Light

  • Definition: Form of energy producing sensation of sight
  • Properties: Rectilinear propagation, dual nature, speed in vacuum ($3 \times 10^8$ m/s)
  • Phenomena: Reflection, Refraction, Dispersion

• Reflection of Light

  • Laws of Reflection
    • Angle of incidence ($i$) = Angle of reflection ($r$)
    • Incident ray, normal, and reflected ray lie in the same plane
  • Spherical Mirrors
    • Types
      • Concave Mirror (Converging)
      • Convex Mirror (Diverging)
    • Key Terms
      • Pole ($P$), Center of Curvature ($C$), Radius of Curvature ($R$)
      • Principal Axis, Principal Focus ($F$), Focal Length ($f$)
      • Relation: $R = 2f$
    • Ray Diagrams & Image Formation
      • Concave: Real/Virtual, Inverted/Erect, Diminished/Enlarged depending on object position
      • Convex: Always Virtual, Erect, and Diminished
    • Mirror Formula
      • $\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$
    • Magnification ($m$)
      • Formula: $m = \frac{h'}{h} = -\frac{v}{u}$
      • Sign conventions: $+ve$ for virtual, $-ve$ for real

• Refraction of Light

  • Phenomenon: Bending of light when passing from one medium to another
  • Laws of Refraction (Snell's Law)
    • Incident ray, refracted ray, and normal lie in the same plane
    • Ratio of $\sin i$ to $\sin r$ is constant ($\frac{\sin i}{\sin r} = n_{21}$)
  • Refractive Index ($n$)
    • Absolute Refractive Index: $n = \frac{c}{v}$
    • Relative Refractive Index: $n_{21} = \frac{v_1}{v_2}$
    • Optically rarer vs. denser medium

• Refraction by Spherical Lenses

  • Types
    • Convex Lens (Converging)
    • Concave Lens (Diverging)
  • Key Terms
    • Optical Center ($O$), Principal Axis, Focus ($F$), Focal Length ($f$)
  • Ray Diagrams & Image Formation
    • Convex Lens: Real/Virtual images based on object distance
    • Concave Lens: Always Virtual, Erect, and Diminished
  • Lens Formula
    • $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
  • Magnification ($m$)
    • Formula: $m = \frac{h'}{h} = \frac{v}{u}$
  • Power of a Lens ($P$)
    • Definition: Reciprocal of focal length in meters ($P = \frac{1}{f}$)
    • Unit: Dioptre ($D$)
    • Combination of lenses: $P = P_1 + P_2 + P_3 + \dots$