Refractive Index Table
Reference values for 'n' and interactive Speed of Light calculator.
Speed of Light
Enter a value or select from table.
v = c / n| Material | n value |
|---|---|
Vacuum Reference | 1.000 |
Air (STP) Gas | 1.000 |
Ice Solid | 1.310 |
Water (20°C) Liquid | 1.333 |
Ethanol Liquid | 1.360 |
Cornea (Human) Biological | 1.376 |
Kerosene Liquid | 1.440 |
Olive Oil Liquid | 1.470 |
Glycerol Liquid | 1.473 |
Plexiglass Solid | 1.490 |
Glass (Crown) Solid | 1.520 |
Salt (NaCl) Solid | 1.544 |
Polycarbonate Solid | 1.584 |
Glass (Flint) Solid | 1.620 |
Sapphire Gemstone | 1.770 |
Ruby Gemstone | 1.770 |
Cubic Zirconia Gemstone | 2.150 |
Diamond Gemstone | 2.417 |
Moissanite Gemstone | 2.650 |
Silicon Solid | 3.440 |
Germanium Solid | 4.000 |
Nothing beats Vacuum.
In a vacuum, light is unstoppable ($c$). But put matter in its way—glass, water, diamond—and it hits the brakes. The Refractive Index ($n$) tells us exactly how hard the brakes are slammed.
The "Car on Mud" Analogy
Why does light bend? Imagine a car driving on pavement (Fast) approaching a patch of mud (Slow) at an angle.
Right wheels hit mud first & slow down.
Left wheels are still fast on pavement.
Result: The car SWERVES (Bends)!
Defining "n"
Refractive Index is fundamentally a ratio of speeds. It has no units.
c = Speed in Vacuum (Fastest)
v = Speed in Material (Slower)
Material Breakdown
| Category | Typical 'n' | Behavior |
|---|---|---|
| Gases (Air) | ~1.0003 | Barely slows light down. Almost vacuum speed. |
| Liquids (Water) | 1.33 - 1.50 | Noticeable bending (Pencils look broken). |
| Solids (Glass/Gems) | 1.50 - 2.42+ | Drastic slowing. High sparkle (Total Reflection). |
Real World Magic: Fiber Optics
The internet (light signals) travels through glass fibers. Because the glass core has a higher refractive index than the outer cladding, light gets trapped inside by Total Internal Reflection. It bounces all the way from New York to London without escaping!
Frequently Asked Questions
What is Refractive Index (n)?
Refractive Index ($n$) is a dimensionless number that describes how fast light travels through a material. It is defined as $n = c / v$, where $c$ is speed in vacuum and $v$ is speed in the medium.
What is the speed of light in Diamond?
Diamond has a high refractive index of $n = 2.42$. Using $v = c/n$, the speed of light in diamond drops to approx. 124,000 km/s (less than half its speed in a vacuum!).
Why does light bend (Refraction)?
Think of a car hitting a patch of mud. If the right wheels hit the mud first, they slow down while the left wheels keep moving fast. This causes the car to turn (bend) towards the mud. Similarly, light bends towards the normal when entering a slower (denser) medium.
What is Total Internal Reflection (TIR)?
When light tries to leave a dense medium (like water) to a rare medium (air) at a steep angle, it can get trapped inside. This happens if the angle of incidence > Critical Angle. Fiber optics use TIR to transport data.
Why does a prism create a rainbow? (Dispersion)
The refractive index depends slightly on wavelength (color). Blue light slows down MORE than Red light (higher $n$). So, Blue light bends more, separating the colors. This is called Dispersion.
Which material has the highest Refractive Index?
Among common gemstones, Moissanite (2.65) and Diamond (2.42) are high. Silicon (3.44) and Germanium (4.0) are much higher but are opaque to visible light (used in Infrared optics).
Does temperature affect Refractive Index?
Yes. Hot air is less dense than cold air. Lower density means lower $n$. This variation causes light to bend gradually in the atmosphere, creating Mirages on hot roads.
Why do diamonds sparkle?
High $n$ means a small Critical Angle (~24°). Light enters but struggles to escape from the bottom, so it bounces around (TIR) and exits the top, reaching your eye as brilliant sparkles.
Is "Optical Density" the same as Mass Density?
No! Kerosene floats on water (lower mass density) but has a higher refractive index (1.44 vs 1.33). Optical density refers purely to how much atoms interact with and slow down light photons.
What uses a lens with High Refractive Index?
High-index lenses are used for strong glasses prescriptions. They bend light more efficiently, so the lens can be made thinner and lighter than standard glass or plastic.