Asked 7 years, 8 months ago. Active 7 years, 8 months ago. Viewed 45k times. Improve this question. Murtuza Vadharia Murtuza Vadharia 1, 3 3 gold badges 16 16 silver badges 33 33 bronze badges. We can tell you that a given material has a certain spectral dispersion variation in index but exactly what causes that can get messy in a hurry. Add a comment. Active Oldest Votes. Yeah it does depend on the the wavelength of light, because: As wavelength of light decreases, the velocity of light decreases.
Improve this answer. Harshal Gajjar Harshal Gajjar 1 1 gold badge 4 4 silver badges 12 12 bronze badges. As presented in the figure above, a wavefront incident upon a plane surface separating two media is refracted upon entering the second medium if the incident wave is oblique to the surface.
There are several important points that can be drawn from this equation. When n 1 is greater than n 2 , the angle of refraction is always larger than the angle of incidence. Alternatively when n 2 is greater than n 1 the angle of refraction is always smaller than the angle of incidence.
In optical microscopy, refractive index is an important variable in calculating numerical aperture, which is a measure of the light-gathering and resolving power of an objective. In most instances, the imaging medium for microscopy is air, but high-magnification objectives often employ oil or a similar liquid between the objective front lens and the specimen to improve resolution.
The numerical aperture equation is given by :. Snell's law was originally defined by the relationship between the incident angles and the ratio of the velocities of light in the two media. However, it is also important to note that light changes direction when it travels from one medium to another. The refractive index of any other medium is defined relative to the refractive index of a vacuum, which is assigned a value of 1.
Thus, a refractive index of 1. Figure 1 : The refraction of light. In this diagram, light travels faster in medium A than it does in medium B. Refractive indices can be measured for different types of mediums including transparent or coloured solutions, turbid suspensions, emulsions, fine powders, ect. The two factors which affect the value of the refractive index are: Temperature Refractive index values are usually determined at standard temperature.
A higher temperature means the liquid becomes less dense and less viscous, causing light to travel faster in the medium. This results in a smaller value for the refractive index due to a smaller ratio. A lower temperature means the liquid becomes denser and has a higher viscosity, causing light to travel slower in the medium.
This results in a larger value for the refractive index due to a larger ratio. Refractometers usually have a means of temperature regulation. Wavelength of light The refractive index varies with wavelength linearly because different wavelengths interfere to different extents with the atoms of the medium.
It is important to use monochromatic light to prevent dispersion of light into different colours. The chosen wavelength should not be absorbed by the medium. The sodium D line at nm is the most frequently used wavelength of light for a refractometer. A refractometer is used to measure the refractive index of a medium.
There are many different types of refractometers, including the Abbe refractometer, which will be discussed in further detail below. 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.
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