In optics, a property of mediums through which light passes, the ratio of the velocity of light in a vacuum (c) to its velocity in the medium. It varies with the wavelength of the light. The symbol is n.
The index of refraction can also be expressed in terms of the permeability and dielectric constant of the medium:
An equation. n equals the fraction c over v, or equals the square root of the fraction
whose numerator is mu times epsilon and whose denominator is mu sub oh time epsilon sub oh,
where μ0 and ε0 represent the permeability and dielectric constant, respectively, of the vacuum.
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Some Examples |
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| Material | Index of refraction at 546.1 nanometers |
| dry air at 15°C, 1 atm pressure | 1.000 277 82 |
| carbon dioxide, STP | 1.000 410 |
| water at 30°C (589 nm) | 1.332 30 |
| fused silica | 1.460 08 |
| Plexiglas | about 1.49 |
| crown glass | 1.513 14 |
| borosilicate crown glass | 1.518 72 |
| crown flint glass | 1.519 78 |
| phosphate crown glass | 1.527 36 |
| polystyrene at 20°C (589 nm) | 1.591 |
| flint glass | 1.607 18 |
| dense crown glass | 1.609 94 |