Notes on Refraction of Light

Refraction of Light

• Light refracts when it travels through transparent materials (e.g., glass).
• Key Angles:
  • Angle of Incidence (I)
  • Angle of Refraction (R)
• Behavior of Light:
  • When entering glass, light slows down and bends towards the normal.
  • When leaving glass, it speeds up and bends away from the normal.
• Frequency of light is unchanged across mediums; wavelength changes with the speed of light.
• Wavelength Relationships:
  • Speed up -> Wavelength increases
  • Slow down -> Wavelength decreases
• Light from less dense to more dense medium:
  • Slows down, bends towards the normal
• Light from more dense to less dense medium:
  • Speeds up, bends away from the normal

Special Cases

• Angle of Incidence = 0:
  • Ray enters along the normal; no change in direction.

Refractive Index

• Defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v).
• Equation:
  • n = c / v (no unit)
• Value of c = 3 x 10^8 m/s
• Refractive index in air is approximately 1.
• Density Relationship:
  • Higher density = Higher refractive index.

Snell's Law

• Formula:
  • n1 * sin(I) = n2 * sin(R)
• Example Calculations:
  1. Light from air (n1 = 1) to glass (n2 = 1.5), I = 60°; R = 35.3°
  2. Light from water (n1 = 1.3) to air (n2 = 1), R = 70°; I = 46.3°
  3. Light from air (n1 = 1) to diamond (n2 = ?), I = 47°, R = 15°; n = 2.8; v = 1.07 x 10^8 m/s

Experiment for Reflection of Light

• Materials: Glass block, paper, light ray, pins.
• Steps:
  1. Trace glass block on paper.
  2. Shine light ray and mark incident/emerging rays.
  3. Measure angles I and R.
  4. Calculate refractive index (n = sin(I) / sin(R)) and speed of light (V = c / n).
  5. Repeat for different angles to find averages or plot sin(I) vs. sin(R).

Critical Angle and Total Internal Reflection

• Light at zero degrees enters along the normal.
• As it reaches point A, some reflects and some refracts.
• Critical Angle (C):
  • Angle of incidence in denser medium where angle of refraction is 90°.
  • Formula: n = 1 / sin(C)
• Total Internal Reflection occurs when angle of incidence exceeds the critical angle.

Applications of Total Internal Reflection

• Periscope:
  • Uses glass prisms; light reflects at 45° angle.
• Binoculars:
  • Multiple total internal reflections; using 45° prisms.
• Rear Reflectors:
  • Reflect light for visibility in vehicles.
• Optical Fibers:
  • Thin glass core with lower refractive index cladding.
  • Used for communication (TV, internet, phones) and medical applications (endoscopy).
  • Allows high-speed information transmission via total internal reflection.

Conclusion

• Understanding refraction, refractive index, and total internal reflection is essential for grasping the behavior of light in various materials.
• Encouraged to engage with content for further learning.