Tabla de contenido
Idiomas disponibles

Idiomas disponibles

3. WORKING PRINCIPLES

Refractometry
!
When a light beam arrives to the divisory
surface between two different mediums, one
part is reflected and the other is bended (it
cames into the second medium), being spre-
ad with an angle and speed different to first
medium. Both values are measured by
Refractive index. Each substance has its own
refractive index value.
!
Refractive index is related to mass, char-
ge and the number of particles in the subs-
tance through which the light beam is transmited. There are different kinds of refracto-
meters but they all are based on the same principle.
!
The basic refractometer principle is based on the following refraction law:
Being n 1 and n 2 medium refractive index at both limit sides between different sides
medium, where α ' is the incident angle and α '' refractive angle.
!
When a light beam enters an optically lighter medium from a thicker one, the incident
angle is smaller than refractive angle and if we change the first one until the second one
reaches 90º, the incident angle is named critical angle.
!
As shown in picture 3, when a light beam falls on surface AB from any angle, its refrac-
tive angle is always bigger than i, if we observe the emergent light beam through a micros-
cope, it appears the view field divided in two halves, one dark and the other one light
Picture 3 - Critical angle
Version 2 December-03
Picture 2
n 1 xsen α '= n 2 xsen α ''
coloured. If we place the two halves separation line
just in the middle, this is the critical angle position.
!
ABDC is the refracting prism whose refractive
index is n 2 , and the sample to be measured (liquid
or transparent solid) is placed on AB surface. Its
refractive index is n 1 .
!
From refraction law, we obtain the following
equation:
Instruction manual 50320XXX
n 1 xsen90º= xsen α
n 2 xsenß = sen i
φ = α + ß
α = φ - ß
Page 13
Tabla de contenido
loading

Tabla de contenido