When light goes to medium
Ȯ
through air with an
Refractive Index of air in the atmospheric pressure
assumed as 1, the ratio of the sine of incident angle
Ș
against the interface to the sine of refractive
angle
ș
is called the Refractive Index of the medium.
Since the Refractive Index changes due to the
temperature, and wavelength of light, it is expressed
as follows:
1. What is a refractometer?
2. Refractive Index and Brix
8
If you put a straw into a glass of water, the straw appears bent. If the water contains
concentrations of sugar, the straw will appear more bent. This is called the "phenomenon of
light refraction". The refractometer applies this principle (if a solution has a higher concentration,
its Refractive Index rises proportionally). The refractometer is a measuring instrument devised
by Dr. Ernst Abbe in Germany in the early 20th century.
2. What is Refractive Index?
3. Brix scale
Note
:
The scale of the NAR-2T is a Brix scale that is based on the Refractive Index of water
(nD=1.33299=Brix 0.0%). Brix means the scale of the weight (%) of sucrose (grams of
sucrose contained in 100 grams of sucrose solution). Thus, if a sucrose solution is
measured, it matches this concentration. However, almost all foods contain not only sugar,
but also a variety of dissolved components such as salt and protein. The total
concentration of these water-soluble materials is called the soluble solid content. When
this sample is measured, Brix is almost consistent with the soluble solid content (%) and is
used as a practical scale.
* The Brix scale is expressed in % mass (Sucrose) as the International System of Units
(SI unit).
For example, the Refractive Index of water at 20
Υ
for the D line is expressed as
ࠉ
= 1.33299
(generally it is expressed in the form of nD=1.33299).
For relation between Brix percentage and refractive and Refractive Index (nD),
refer to page 49.
boundary
air
medium
Ȯ
Ș
ș
㹬
=1
㹬
=
sin
Ș
sin
ș
n
20
D
n
t
D
n : Represents the Refractive Index
t : Temperature(
Υ
)
D : D- line of sodium
Note:
The Refractive Index measured by setting the
Refractive Index of vacuum to 1 is called the
absolute Refractive Index, but it is generally
scarcely used.
