B Tech Applied Science: Physics

Unit 1: Refraction and Total Internal Reflection

Introduction

• Topics Covered: Refraction and Total Internal Reflection (TIR)
• Initial Quiz: Identify wave behaviors in diagrams

Key Concepts

Refraction

• Definition: A wave changes direction when passing through a different medium
• Example: Light entering glass from air
• Behavior:
  • When entering a denser medium (e.g., air to glass), light bends towards the normal
  • When entering a less dense medium (e.g., glass to air), light bends away from the normal
  • Reason: Wave speed decreases in denser mediums
• Speed of Light:
  • In vacuum: (3 \times 10^8) m/s
  • In water: (2.25 \times 10^8) m/s
  • Water is optically denser than air

Refractive Index

• Formula: (n = \frac{c}{v})
  • (c): Speed of light in vacuum
  • (v): Speed of light in medium
• Refractive Index of Water: 1.33
• Relation with Angles: (n = \frac{\sin i}{\sin r})
  • (i): Angle of incidence
  • (r): Angle of refraction
  • (\sin i > \sin r) for (n > 1)
  • Angles measured between ray and normal

Total Internal Reflection (TIR)

• Occurs When:
  • Light cannot refract beyond 90°
  • Light reflects within the medium
• Critical Angle:
  • Maximum angle of incidence before TIR occurs
  • (\sin C = \frac{1}{n})
  • Calculate for different materials:
    • Water: 48.8°
    • Glass: 41.8°
    • Diamond: 24.6°

Applications of Total Internal Reflection

Optical Fibers

• Structure: Glass fibers that trap light
• Use:
  • Light remains inside fiber due to TIR
  • Allows light to travel around corners
• Applications:
  • Communication:
    • Fiber optic cables carry digital signals (e.g., TV programs, telephone)
  • Medical Use:
    • Endoscopy for internal body examination without surgery

Summary

• Understand how light behaves when transitioning between different mediums
• Calculate refractive index and critical angles
• Recognize the practical uses of TIR in technology and medicine