Working Principle Behind the Abbe Refractometer

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A refractometer is an instrument which measures refractive index by making use of total internal reflection. Pulfrich designed a refractometer enabling the refractive index of a liquid to be easily obtained, which consists of a block of glass G with a polished and vertical face. On top of G is cemented a circular glass tube V. The liquid L is placed in V, and a convergent beam of monochromatic light is directed so that the liquid-glass interface is illuminated. On observing the light refracted through G by a telescope T, a dark and light field of view are seen.


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Abbe designed a refractometer for measuring the refractive index of liquids whose principle is illustrated as follows:

Two similar prisms X, Y are placed on a table A, the prism X being hinged at H so that it could be swung away from Y, A drop of the liquid is placed on the surface a, which is matt, and the prisms are placed together so that the liquid is squeezed into a thin film between them. Light from suitable source is directed towards the prisms by means of a mirror m, where it strikes the surface a, and is scattered by the matt surface into the liquid film. The emergent rays are collected in a telescope T directed towards the prisms, and the field of view is divided into a dark and bright portion. The table A is then turned until the dividing line between the dark and bright fields is on the crosswires of the telescope, which is fixed. The reading on a scale S, which is attached to, and moves with, the table, gives the refractive index of the liquid directly.


About the Author

Tony Onwujiariri
Tony is an Avid Tech enthusiast that loves Scientific Inventions and Tech Products. He blogs Passionately on Science and Technology related niches and spends most of his time on Research in Content Management and SEO. Tony loves Sugar and has been in love with Don Williams since he was a toddler on Diapers.

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