Why is index of refraction important

The angle of incidence of each individual light ray is denoted by i and the angle of refraction by r. The four yellow light rays all have an angle of incidence i low enough to pass through the interface between the two media. However, the two red light rays have incident angles that exceed the critical angle approximately 41 degrees and are reflected either into the boundary between the media or back into the high refractive index medium. This phenomenon takes place when the angle of refraction angle r in Figure 4 becomes equal to 90 degrees and Snell's law reduces to:.

As discussed previously, another important feature of light refraction is that the wavelength of light has an impact on the amount of refraction that occurs within a medium. In fact, the amount of refraction that takes place is inversely proportional to the wavelength of the incident light.

Thus, shorter wavelength visible light is refracted at a greater angle than longer wavelength light. Consequently, when white light, which is composed of all the colors in the visible spectrum, is passed through a glass prism, it is dispersed into its component colors in a manner that is dependent upon the individual wavelengths. Low frequency visible light nanometers and greater is refracted at a smaller angle than higher frequency light, which results in a rainbow-like effect, as illustrated below in Figure 5.

This same phenomenon is also responsible for chromatic aberration. When white light is passed through a simple convex lens, several focal points arise in close proximity that correspond to the minor refractive index differences of the component wavelengths. This effect tends to produce colored either red or blue, depending upon focus halos surrounding the images of objects.

Correction of this aberration is usually accomplished through the use of combinations of two or more lens elements composed of materials having different dispersive properties, such as an achromatic lens constructed with both crown and flint glasses. Over the years, humans have made many devices that make use of the fact that light can be refracted, as well as reflected and focused. The most common example is a camera, which is designed to create sharp and focused images onto an emulsion of film or the surface of a charge-coupled device CCD to produce an accurate image.

Other optical devices that exploit these characteristics of light include microscopes and telescopes, which enable the viewing of of objects that are invisible to the unaided human eye, regardless of whether they are located on the head of a pin or in a distant galaxy.

Mortimer Abramowitz - Olympus America, Inc. Shannon H. Neaves and Michael W. Visit the Molecular Expressions Website. Photo Gallery. Silicon Zoo. Chip Shots. Screen Savers. To generate a defined wavelength, refractometers most often use the sodium D-line, which corresponds to Due to the fact that it is a widely available, reliable and stable light source, the sodium D-line has long been used in the study of refractive index.

Every material that interacts with light has a refractive index. In many industries, a refractive index measurement is used to check the purity and concentration of liquid, semi-liquid and solid samples. Liquids and semi-liquid samples can be measured with high accuracy e. In addition, the index of refraction can be correlated to a wide range of concentrations which can be used to characterize many different samples in many different industries and applications, such as:.

Additionally, for some applications, combining refractive index with a density measurement creates a simple yet powerful quality control technique. These determinations can be fully automated. Learn more about their differences, calculations, usage and how to measure. Absolute refractive index is calculated with reference to the vacuum in which light propagates with the greatest possible speed of ,, meters per second the speed of light. However, in practice, the air we breathe is also considered a reference medium, even though light propagates at a slightly slower speed 1.

Thus, we can say that the absolute refractive index measures how many times the speed of light is greater in a vacuum or air than in any other media. Relative refractive index is defined as the ratio of the light velocities between any two media other than a vaccum or air. For example, one could measure the refractive index of olive oil relative to the refractive index of water.

However, there is no practical use for measuring relative refractive index in industrial applications. Modern digital instruments can easily determine the refractive index of liquids with a high degree of accuracy.

However, high-resolution instruments are no guarantee of accurate results. Good measurement principles must also be applied. For example, did you know that insufficient cleaning of the prism—or simply wiping off old sample with a cloth—can drastically falsify your next measurement?

Because these instruments measure the angle of total reflection off the surface of the prism, even the thinnest layer of old sample will have a significant impact on the refractive index measurement of any new sample added to it.

Download the Refractive Index Measurement Guide and learn helpful tips and hints to avoid errors when measuring the refractive index of liquids. Whether you work with chemicals, foods, beverages, or other products that can be pasty or liquid, there are important details that need to be addressed in order to improve your refractive index analyses.

These include questions such as:. The answers to these questions can directly influence your determinations. Check out our interactive booklet that answers the most-asked questions about refractive index, Brix and density measurements! A high refractive index means that a light beam travelling through medium media moves slowly.

In practice the more concentraded a binary substance is, the higher it's refractive index. If your liquid sample contains solid suspenses, it is recommended to pour the sample into the refractometer sample stage and wait for a fixed period of time e. Yes, black, dark and colored samples can be measured within seconds with a digital refractometer. Refractive index can easily be used to identify a pure sample because each element has a unique refractive index.

After a measurement, the index of refraction of the sample in question can be looked up to see what it corresponds to. In addition, when using an automatic refractometer refractive index can be automatically converted into other scales e. Automated Reactors and In Situ Analysis. Transport and Logistics. Expertise Library. Literature: White Papers, Guides, Brochures.

Technical Documentation. 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.

How is a refractive index measured? Open prism assembly and remove lens tissue. Inspect the prism for cleanliness. If necessary, clean with water, methanol or acetone. Place liquid sample on the depression in the lower prism, using a pipette, and close the prisms. As the refractive index of a material increases, the greater the extent to which a light beam is deflected or refracted upon entering or leaving the material. The refractive index of a medium is dependent to some extent upon the frequency of light passing through, with the highest frequencies having the highest values of n.

For example, in ordinary glass the refractive index for violet light is about one percent greater than that for red light.

A consequence of this phenomenon is that each wavelength experiences a slightly different degree of refraction when a heterogeneous light beam containing more than one frequency enters or leaves the medium. This effect is termed dispersion and is responsible for chromatic aberration in microscope objectives. Michael W.