Function And Construction Of The Refractometer - Optica 2WAJ Manual De Instrucciones

5.0 FUNCTION AND CONSTRUCTION OF THE REFRACTOMETER

5.1 Refractive index
The refractive index of a material is the factor by which the phase velocity of electromagnetic
radiation is slowed in that material, relative to its velocity in a vacuum.
When a light beam travels between two media of differing refractive index, n
angle of incidence, a1, that is not perpendicular with the surface, the beam will be deviated
according to the refractive law (Snell's law):
Where a , is the angle of refraction measured with respect to the normal to the surface.
2
When a light beam enters from optically denser medium to optically thinner one, the angle of
incidence is smaller than the refractive angle. Increasing the angle of incidence will lead us to
a point where the angle of refraction will be 90°C. In this case, the angle of incidence is called
a critical angle. Beyond this angle total reflection will occur and no light will be transmitted to
the second medium.
This principle is used by the refractometer in or-
der to determine the refractive indices. In the
refractometer light beams from different angles
fall upon the surface, its refractive angles are
always greater than 90°. A telescope is used to
observe the emerging beam and a bright and
dark image can be observed in the field of view
in the telescope, appearing as distinct boundary
line in between, as indicated in fig. 2. The boun-
dary line between the brightness and the dark-
ness is just the position of the critical angle.
5.2 Construction of the optical system
The optical system of the instrument consists of the telescopic and the reading systems as
shown in fig. 3. All optical components and other main structures except the prism and the
eyepieces are mounted inside the housing.
SURFACE
BETWEEN MEDIA
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and n , with an
1 2
NORMAL
Fig.1
Fig.2