RRB NTPC GROUP D : Refractive indices of materials

Refractive index

Definition

The refractive index n of an optical medium is defined as the ratio of the speed of light in vacuum, c = 299792458 m/s, and the phase velocity v of light in the medium

${\displaystyle n={\frac {c}{v}}.}$

The phase velocity is the speed at which the crests or the phase of the wave moves, which may be different from the group velocity, the speed at which the pulse of light or the envelope of the wave moves.

Material	n
Vacuum	1
Gases at 0 °C and 1 atm
Air	1.000293
Helium	1.000036
Hydrogen	1.000132
Carbon dioxide	1.00045
Liquids at 20 °C
Water	1.333
Ethanol	1.36
Olive oil	1.47
Solids
Ice	1.31
Fused silica (quartz)	1.46
PMMA (acrylic, plexiglas, lucite, perspex)	1.49
Window glass	1.52[12]
Polycarbonate (Lexan™)	1.58[
Flint glass (typical)	1.62
Sapphire	1.77
Cubic zirconia	2.15
Diamond	2.42
Moissanite	2.65