Reflection & Refraction
BeginnerUnderstand how light behaves when it encounters boundaries between different materials.
Reflection & Refraction Visualization
Incident Ray
Reflected Ray
Refracted Ray
Parameters
Calculations
Incident Angle
30°
From normal
Reflected Angle
30°
θᵢ = θᵣ
Refracted Angle
19.5°
Snell's law
Critical Angle
N/A
For TIR
Snell's Law Verification
n₁ sin(θ₁) = n₂ sin(θ₂)
1.00 × sin(30°) = 1.50 × sin(19.5°)
0.5000 = 0.5000
💡 Tips:
- Into denser medium (n₂ > n₁): Light bends toward the normal
- Into less dense (n₂ < n₁): Light bends away from the normal
- Total internal reflection: Set n₁ > n₂ and increase angle past critical angle
- Law of reflection: Angle of incidence always equals angle of reflection
- Try air→water (1.0→1.33), water→air (1.33→1.0), or air→diamond (1.0→2.42)
- Critical angle only exists when going from denser to less dense medium
Theory
Snell's Law of Refraction
When light passes from one medium to another, it changes direction according to the refractive indices of the two media.
Snell's Law: n₁ sin(θ₁) = n₂ sin(θ₂)
Refractive Index: n = c / v
Critical Angle: θc = sin⁻¹(n₂ / n₁) when n₁ > n₂
Total Internal Reflection: Occurs when θ₁ > θc
Law of Reflection
When light reflects off a surface, the angle of incidence equals the angle of reflection:
- θincident = θreflected
- Incident ray, reflected ray, and normal all lie in the same plane
- Works for all types of surfaces (mirrors, water, glass, etc.)
Refraction Principles
When light enters a different medium, it bends according to the refractive indices:
- Into denser medium (n₂ > n₁): Light bends toward the normal
- Into less dense medium (n₂ < n₁): Light bends away from the normal
- Same refractive index: No bending, light continues straight
- Speed changes: Light slows down in denser media (higher n)
Total Internal Reflection
A special phenomenon that occurs when light travels from a denser to a less dense medium:
Conditions Required
- • Light traveling from denser to less dense medium
- • Angle of incidence > critical angle
- • 100% of light is reflected internally
Applications
- • Optical fibers for data transmission
- • Binoculars and periscopes (prisms)
- • Diamond brilliance
Common Refractive Indices
| Material | Refractive Index (n) | Speed of Light |
|---|---|---|
| Vacuum | 1.00 | 3.0 × 10⁸ m/s |
| Air | 1.0003 | ≈ 3.0 × 10⁸ m/s |
| Water | 1.33 | 2.25 × 10⁸ m/s |
| Glass (typical) | 1.5 | 2.0 × 10⁸ m/s |
| Diamond | 2.42 | 1.24 × 10⁸ m/s |
Real-World Applications
- Optical fibers: Use total internal reflection to transmit data over long distances
- Lenses: Cameras, eyeglasses, microscopes all rely on refraction
- Rainbows: Refraction and reflection inside water droplets
- Mirages: Refraction in air layers of different temperatures
- Prisms: Separate white light into colors due to wavelength-dependent refraction
- Underwater vision: Why things look distorted when viewed from different media
- Diamonds: High refractive index creates brilliance through total internal reflection