20.1 Refractive Index properties and terminology
Description
This article is from the Chemistry FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous contributions by others.
20.1 Refractive Index properties and terminology
When light passes between media of different density, the direction of the
beam is changed as it passes through the surface, and this is called
refraction. In the first medium, the angle between the light ray and the
perpendicular is called the angle of incidence (i), and the corresponding
angle in the second medium is called the angle of refraction (r). The
ratio sine i / sine r is called the index of refraction, and usually the
assumption is that the light is travelling from the less dense (air) to more
dense, giving an index of refraction that is greater than 1. Although the
theoretical reference is a vacuum, air ( 0.03% different ) is usually used.
The refractive index of a compound decreases with increasing wavelength
( dispersion ), except where absorption occurs, thus the wavelength should
be reported. The D lines of sodium are commonly used.
The refractive index of a liquid varies with temperature and pressure, but
the specific refraction ( Lorentz and Lorentz equation ) does not. The molar
refraction is the specific refraction multiplied by the molecular weight,
and is approximately an additive property of the groups or elements
comprising the compound. Tables of atomic refractions are available in the
literature, as are descriptions of the common types of refractometers [1].
Continue to:
My Books
