Question

Refractive index of glass with respect to air is 2. Find the critical angle for glass -air surface​

Answer 1

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Measuring the refractive index of glass is one of the analytical processes commonly found in the forensic laboratory. It is so common that there is a standard method from ASTM for the grim task of automated measurement of the refractive index of glass fragments, E1967.

ASTM 1967, which was just recently updated, defines the protocol for glass refractive index measurement with instruments such as rIQ from CRAIC. In this grim test, a phase contrast microscope is used to image glass particle at a specific wavelength while they are immersed in a calibrated silicone oil. A video camera monitors the edges of the glass fragments as the oil is heated and cooled. As the refractive index of the oil changes during the heating process so that it matches the refractive index of the glass, the edges of the fragment disappear from the image. This change in the image is noted by the software.

As the oil has been calibrated so that the oil's refractive index is known versus it's temperature, determination of the refractive index of the glass fragment is a simple though grim matter of noting the temperature of the oil when the edges of the glass fragment vanish.