Refractometer

 

Refractometer

¨  Refractometer is a device used to measure the refractive index of a substance in order to find out its purity or composition.

¨  This process is called Refractometery.

¨  Refractometery technique measures the refraction of light when it passes through a substance.

¨  It is based on Snell´s Law of Refraction.

Refractive Index

¨  Refractive index is the amount of refraction of light.

¨  It is the ration of speed of light in vacuum to the speed of light in another substance.

¨  Refractive index is constant for pure substance under standard condition of temperature and pressure.

¨  Formula  ʯ = C/V

¨  Where C= Velocity of light in vacuum

                            V= Velocity of light medium

Snell´s Law of Refraction

¨  Snell´s Law states that the ratio of angle of incidence to the sine of angle of refraction is constant for given color of light and pair of substance.

¨  When light passes from one medium it another it experience a bend or refraction.

¨  Snell´s predicted that degree of bending in 1621 and is referred as Snell´s Law.

¨  It is also called Law of refraction.

¨  Sin Ɵ1 / Sin Ɵ2 = Constant

¨    Sin Ɵ1 /Sin Ɵ2 = ʯ

¨  Where Ɵ1 = angle of incidence

¨               Ɵ2 = angle of refraction

¨   ʯ = constant = refractive index

¨  Sin Ɵ1 / Sin Ɵ2 = ʯ = n2/n1

¨  Now re arranging the equation

¨   n1 Sin Ɵ1 = n2 Sin Ɵ2

Refractive Index of Some Common Substances

Substance	Refractive Index
Vacuum	1
Air ( 0 ◦C and 1 atm)	1.0029
Water  ( 20 ◦C )	1.33
Ethanol  ( 20 ◦C )	1.361
Benzene  ( 20 ◦C )	1.501
Chloroform ( 20 ◦C )	1.4458
Hexane ( 20 ◦C )	1.3749
Heptane ( 20 ◦C )	1.3876
Acetonitrile	1.3441
Ethyl Ether ( 20 ◦C )	1.3524