can somebody explain to me how a refractometer works, please?

Answer 1

A simple refractometer typically involves a prism (or a grating), a turntable, an objective lens and an image lens.

The objective lens focuses light onto the prism/grating which refracts the light. The imaging collimator and lens is placed at the angle where the refraction occurs (by looking for the light) and, therefore, tells you the angle. From that, details about the refractive index can be determined.

Answer 2

A refractometer is a simple instrument used for measuring concentrations of aqueous solutions.
It requires only a few drops of liquid, and is used throughout the food, agricultural, chemical,
and manufacturing industries.
When light enters a liquid it changes direction; this is called refraction. Refractometers measure the degree to which the light changes direction, called the angle of refraction. A refractometer takes the refraction angles and correlates them to refractive index (nD) values that have been established. Using these values, you can determine the concentrations of solutions. For example, solutions have different refractive indexes depending on their concentration in water.

The prism in the refractometer has a greater refractive index than the solution. Measurements are read at the point where the prism and solution meet. With a low concentration solution, the refractive index of the prism is much greater than that of the sample, creating a large refraction angle and a low reading. The reverse would happen with a high concentration solution.

Answer 3

My first Science fair project was to build a refractometer. That simple device consisted of a semicircle of transparent plastic and a light source. The light source was positioned to shine on the center of the flat side of the semicircle of plastic. Rotating the semicircle in the plane of the circle allowed me to create different angles of incidence. As the angle of incidence approached a certain angle, the light stopped penetrating the plastic and was instead reflected. This angle was a property of the plastic I was using. The critical angle of total reflection was determined by the refractive index of the plastic. More accurate devices would take into account the frequency of the light being used.
A refractometer would need to be built differently to deal with testing materials in the three different material phases. A device that was good at testing gasses would probably not do a good job of testing solids. A device to test gasses and liquids could be made with a semicircular tank to hold the liquid and angles could be measured relative to the tank. The bending of the light beam as it traveled through the liquid or gas might also be possible. A device to test solids would need to be able to measure angles relative to the surface of the solid and would be restricted to finding the critical angle of total reflection.