How does the Becke line determine refractive index?
The Becke line test is a technique in optical mineralogy that helps determine the relative refractive index of two materials. It is done by lowering the stage (increasing the focal distance) of the petrographic microscope and observing which direction the light appears to move.
What do Becke lines look like?
Becke Lines – Are defined as the broad, dark or bright lines (due to refraction and/or diffraction) formed in the image at the boundary between media of different optical path lengths. They move in the direction of the longer optical path when the distance between the objective and the object is increased.
How do you see Becke lines?
When the RI of the mineral and the RI of the mounting material are equal, the Becke line splits into two lines, a blue line and an orange line. In order to see the Becke line the microscope is slightly out of focus, the grain appears fuzzy, and the two Becke lines are visible.
What does it mean if a Becke line is present?
A Becke line is a halo-like ring of refracted light that appears when a piece of glass is submerged in liquid and viewed under a compound microscope. b. A Becke line forms when refracted light concentrates around the edges of a piece of glass.
What technique is used for determining the refractive index of glass?
A Refractometer is the instrument used to measure refractive index (RI). A refractometer measures the extent to which light is bent when it moves from air into a sample and is typically used to determine the refractive index of a liquid sample.
Which method of testing glass is most effective in determining the refractive index of glass?
The flotation and immersion methods are best used to determine a glass fragment’s density and refractive index, respectively.
What is refractive index in forensics?
10 pages. This report presents guidelines for measuring the refractive index (the ratio of the speed of light in one media compared to another for a particular transparent medium) of forensic glass samples. Refractive index is the most commonly measured property in the forensic analysis of glass.
How can the dispersion method be used to measure the refractive index of a mineral?
The refraction index of Diamond (measured with nD – or the Fraunhofer D-line) gives a refraction index of 2.417. The value for red light (nB) in a Diamond is measured at 2.407 and for violet light (nG) it is measured at 2.451….Dispersion of Some Common Gem Minerals.
| Gem Mineral | Dispersion |
|---|---|
| Zincite | 0.127 |
| Zircon | 0.039 |
What does a Becke line tell you when analyzing glass samples?
Becke line – Indication of Refractive Index Notice the halo of light on the inside perimeter of the glass sample. When the Becke line is inside the perimeter of the glass fragment, the refractive index of the glass is higher than the refractive index of the surrounding medium.
What is refractive index method?
Refractive Index Measurement or Refractometry is the method of measuring substances refractive index and assess their composition or purity. Refractometry is a technique that measures how light is refracted when it passes through a given substance.
What are the two most common methods of glass analysis?
How is RI measured?
How do you find the refractive index of a mineral?
Abstract. The ordinary immersion method of determining index of refraction consists in comparing the index of a mineral with those of a series of liquids with the final result that the index of the mineral is equal to that of one of the series of liquids or lies between those of two consecutive liquids.
What is refractive index What are the different methods to determine it?
The refractive index is the measure of bending of a light ray when passing from one medium to another. It can also be defined as the ratio of the velocity of a light ray in an empty space to the velocity of light in a substance, n = c/v.
What is the refractive index of a glass fragment?
Index of Refraction Ranges for Several Types of Glasses Glass Index of Refraction Headlight glass 1.47-1.49 Television glass 1.49-1.51 Window glass 1.51-1.52 Bottles 1.51-1.52 Ophthalmic lenses 1.52-1.53 Table taken from Saferstein, R., Criminalistics Lab Manual, p.
What is the symbol of refractive index?
Refractive Index (Index of Refraction) is a value calculated from the ratio of the speed of light in a vacuum to that in a second medium of greater density. The refractive index variable is most commonly symbolized by the letter n or n’ in descriptive text and mathematical equations.