Medium directly in contact with the unknown sample, are used to determine the refractive index of the unknown sample This measurement combined with the knowledge of the refractive index of the This instrument measures the angle of refraction of light Principle that light bends when it enters a different medium. Including the Abbe refractometer, which will be discussed in further detail below. There are many different types of refractometers, Where t = temperature in ✬ and D = the wavelength of the light used in nm.Ī refractometer is used to measure the refractive index of a medium.

Note: These two factors are present in the equation above, The sodium D line at 598 nm is the most frequently used wavelength of light for a refractometer.The chosen wavelength should not be absorbed by the medium.It is important to use monochromatic light to prevent dispersion of light into different colours.The refractive index varies with wavelength linearly because different wavelengths interfere to different extents with the atoms of the medium.Refractometers usually have a means of temperature regulation.This results in a larger value for the refractive index due to a larger 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 smaller value for the refractive index due to a smaller ratio. A higher temperature means the liquid becomes less dense and less viscous, causing light to travel faster in the medium.Refractive index values are usually determined at standard temperature.The two factors which affect the value of the refractive index are: Turbid suspensions, emulsions, fine powders, ect.įactors that affect the refractive index: Refractive indices can be measured for different types of mediums including transparent or coloured solutions, Thus, a refractive index of 1.33 for water means that light travels 1.33įigure 1: The refraction of light. The refractive index of any other medium is defined relative to the refractive index of a vacuum, Which will be very important later in our discussion of refractometers. Therefore, another method to calculate the refractive index of a medium is to apply Snell’s law, However, it is also important to note that light changes direction when it travels from one medium to another. The refractive index ( )Ĭan be calculated using the equation below. Light travels through another medium other than a vacuum, the atoms of that medium constantly absorbĪnd reemit the particles of light, slowing down the speed light travels at. This change in speed from one medium to another is what causes light rays to bend. The refractive index is a ratio of the speed of light in a medium relative to its speed in a vacuum.

Index of reflection calculator