A refractometer works based on the principle that light bends when it enters a different medium. This instrument measures the angle of refraction of light rays passing through the unknown sample.
The following cross sectional diagram illustrates the inner-workings of a refractometer. A light source shines on the illuminating prism and light rays enter the sample moving in different directions. The other light rays entering the refracting prism all have a smaller refraction angle and lie to the left of point C. A detector at the back of the refracting prism produces the light and dark regions.
In an Abbe refractometer, a detector is not present and there is more optics but the general scheme remains the same. Samples with different refractive indexes produce different angles of refraction which will cause a shift in the borderline between the light and dark regions.
Figure 2 : A cross-sectional diagram of part of the optical path of an Abbe refractometer. The sample thickness has been exaggerated for clarity. Since refractive indices vary with temperature, for each degree Celsius of temperature change, the average temperature correction has been found to be 0. If the reading for the refractive index was 1.
Many refractometers have a theromometer and a means of circulating water to maintain a specific temperature. This video illustrates step by step the usage of an Abbe 3L Bausch and Lomb refractometer. This is a good webpage for the most common problems when setting up your refractometer.
Refractive indices have many purposes and are used most frequently to differentiate between liquid samples. Therefore, this physical quantity characterizes liquids in the same way that melting points are used to characterize solids.
This measurement can serve as a means of identification of a substance by comparing its refractive index to known literature values. Finally, refractive indices are influenced by the polarizability of a medium. The more polarizable the material, the higher the refractive index is for the substance. Thus, knowledge of the refractive index of a substance is also necessary to calculate dipole moments of that substance. The molar refractions, R, can be calculated and are characteristic of that substance and indicative of its structure.
Skip to main content. Refractive Index Theory Your browser does not support the embed tag What is a refractive index? Factors that affect the refractive index: The two factors which affect the value of the refractive index are: Temperature Refractive index values are usually determined at standard temperature.
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Create a free Team What is Teams? Learn more. Why is the index of refraction different for different wavelengths? Asked 6 years, 3 months ago. Active 6 years, 3 months ago. Viewed 52k times. Improve this question. Add a comment.
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