Refraction
Physics · अपवर्तन
📋Quick Overview
Refraction is the bending of light when it passes from one medium to another (e.g., air to water). This happens because light travels at DIFFERENT speeds in different media. Light is fastest in vacuum (3 × 10⁸ m/s), slower in air, even slower in water, and slowest in glass/diamond. When light enters a denser medium, it bends TOWARDS the normal. When it enters a rarer medium, it bends AWAY from normal.
📖Snell's Law & Refractive Index
Snell's Law: n₁ sin i = n₂ sin r, where n = refractive index, i = angle of incidence, r = angle of refraction. Refractive Index (n) = Speed of light in vacuum / Speed of light in medium. Higher n = denser medium = light bends more.
| Medium | Refractive Index (n) | Light Speed |
|---|---|---|
| Vacuum | 1.00 (reference) | 3 × 10⁸ m/s (fastest) |
| Air | 1.0003 (≈1) | Nearly same as vacuum |
| Water | 1.33 | 2.25 × 10⁸ m/s |
| Glass | 1.5 | 2 × 10⁸ m/s |
| Diamond | 2.42 (highest natural) | 1.24 × 10⁸ m/s (slowest) |
📝Total Internal Reflection (TIR)
- •When light goes from DENSER to RARER medium at angle greater than the critical angle, it is totally reflected back — no refraction occurs!
- •Two conditions: (1) Light must go from denser to rarer, (2) Angle of incidence > critical angle
- •Applications: Optical Fiber (internet cables), Mirage in desert, Diamond sparkle, Periscope (using prisms)
- •Optical fiber uses TIR to carry light signals over long distances without loss — basis of internet!
- •Diamond sparkles because its critical angle is very small (24.4°), so most light undergoes TIR inside the diamond
📝Daily Life Examples of Refraction
- •Pencil in water looks BENT — because light bends when going from water to air
- •Pool/river looks SHALLOWER than actual — objects in water appear closer to surface
- •Stars TWINKLE due to atmospheric refraction (light bends through different air layers)
- •Sun appears before actual sunrise and after actual sunset — due to atmospheric refraction
- •MIRAGE: In deserts, hot air near ground is rarer → light bends upward → creates illusion of water
- •Rainbow is caused by dispersion (splitting) of white light by raindrops into 7 colors (VIBGYOR)