12/25/2023 0 Comments Hydrometer fruitjuice![]() Although more complex mixtures may produce less accurate determinations, refractometers can still give acceptable approximations of solute concentration, suitable for quality control. When the test sample is a simple mixture of two components, such as water and sugar or water and alcohol, the first choice for their characterization is a refractometer. The refractive index is specific to a substance, making this property an easy and efficient method to characterize materials and evaluate their purity. How to use a refractometer, specific gravity and what it tells us Refracted beams are shown in red, the beam at the critical angle in black and reflected beams in purple. 1įigure 2: Representation of light refraction and reflection in relation to the critical point (A) and observation of the critical angle through reflected light on a prism (B). Therefore, care must be taken to control or compensate for temperature variations and wavelength. To determine the refractive index of a substance accurately, additional considerations must be made, in particular due to the dependency of this property on the temperature and the wavelength of light used to measure it. This relation establishes the working principle of most refractometers. ![]() By knowing the refractive index of the prism ( n A) as well as the refraction angle θ B at the critical angle (i.e., 90°), the refractive index of the liquid ( n B) can now be determined. When observed from the right position, the critical angle can be visualized as a transition between dark and light regions. 3 If we now consider an illuminated prism in contact with a liquid (Figure 2B), the beams traveling below the critical angle are refracted and the beams traveling above the critical angle are reflected. At this particular point, known as the critical angle, the light beam travels parallel to the interface and any additional increase in the angle of incidence will result in reflection of the light. At a specific angle of incidence, the refraction angle reaches 90 °, which is the maximum refraction angle possible. As the angle of an incident light beam increases, so does the refraction angle (see Figure 2A). To understand the working principles of refractometers better, there is another fundamental concept to consider, the critical angle. The above equation shows that the refractive index of a substance can be found by measuring the angles of incidence and refraction rather than measuring the speed of light. 2 Considering a perpendicular plane to the interface, the incident and refracted beams form angles θ A and θ B, and the refractive indices of media A and B ( n A and n B), the following relation can be established (Equation 2): Credit: The Author.Īccording to Snell's law, the relation between the sines of the angle of incidence and angle of refraction is equal to the refractive index of the second medium. This phenomenon is represented by Figure 1, where a light beam travels through media A and B at the velocities v A and v B respectively.įigure 1: Light refraction at the interface between medium A and medium B. ![]() When light travels from one medium to another, it changes not only in speed but also in direction, resulting in refraction. Refractive index (n) = (Speed of light in a vacuum)Įquation 1: Definition of the refractive index of a substance using light speeds. The refractive index of a substance is determined by the ratio of the speed of light in a vacuum to the speed of light traveling through the test substance, as described in Equation 1. How does a refractometer work, the index of refraction and role of Snell’s law ![]()
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