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Physics > Refractive Indices

The refractive index of a medium (material) is a measure for how much the speed of light (or other waves) is reduced inside the medium. Standard glass has a refractive index of 1.5, which means that light travels at 1 / 1.5 = 0.67 times the speed in air or vacuum. Two common properties of glass and other transparent materials are directly related to their refractive index. First, light rays change direction when they cross the interface from air to the material, an effect that is used in lenses. Second, light reflects partially from surfaces that have a refractive index different from that of their surroundings.

The table below shows the refractive indices of common materials:

Material Refractive Index (n)
Vacuum 1.00000 (exactly)
Air (STP) 1.00029
Acetone 1.36
Alcohol 1.329
Chromium Oxide 2.705
Copper Oxide 2.705
Crown Glass 1.52
Crystal 2.00
Diamond 2.417
Emerald 1.57
Ethyl Alcohol 1.36
Fused Quartz 1.46
Heaviest Flint Glass 1.89
Heavy Flint Glass 1.65
Glass 1.5
Ice 1.309
Iodine Crystal 3.34
Liquid Carbon Dioxide 1.20
Polystyrene 1.55
Quartz 1.644
Ruby 1.77
Sapphire 1.77
Sodium Chloride (Salt) 1.544
Sugar Solution (30%) 1.38
Sugar Solution (80%) 1.49
Topaz 1.61
Water (20°C) 1.333
Zinc Crown Glass 1.517