What is refractive index?
In optics the refractive index or index of refraction n of a substance (optical medium) is a dimensionless number that describes how light, or any other radiation, propagates through that medium. It is defined as ,
where c is the speed of light in vacuum
v is the speed of light in the substance
example, the refractive index of water is 1.33, meaning that light travels 1.33 times as fast in vacuum as it does in water The historically first occurrence of the refractive index was in Snell's law of refraction, n1sinθ1= n2sinθ2, where θ1 and θ2 are the angles of incidence of a ray crossing the interface between two media with refractive indicesn1 and n2.
Incident ray:- In the diagram, the ray of light approaching the surface of medium is known as the incident ray . Refracted ray:- The ray of light that leaves the surface of medium is known as the reflected ray Critical angle:- the angle of incidence above which total internal reflection occurs. It is also defined as tthe angle of incidence that provides an angle of refraction of 90-degrees Example:-
For the water-air boundary, the critical angle is 48.6-degrees. For the crown glass-water boundary, the critical angle is 61.0-degrees. ni *• sine() = nr • sine ()
ni • sine() = nr • sine (90 degrees)
ni • sine() = nr
sine() = nr/ni
= sine-1 (nr/ni) = invsine (nr/ni)
Total internal reflection:- Total internal reflection is a phenomenon that happens when a propagating wave strikes a medium boundary at an angle larger than a particular critical anglewith respect to the normal to the surface. Some important features of refractive index
1. Refractive index of materials varies with the wavelength. This is called dispersion; it causes the splitting of white light in prisms and rainbows, and chromatic aberration in lenses 2. The refractive index of a material is the most important property of any optical system that uses refraction. 3. It is used to calculate the focusing power of lenses, and the dispersive power of prisms. 4. It can also be used as a useful tool to differentiate between different types of gemstone 5. It is a fundamental physical property of a substance, it is often used to identify a particular substance, confirm its purity, or measure its concentration 6. commonly it is used to measure the concentration of a solute in an aqueous solution principle of refractive index measurement
When studying the wave nature of light, Dutch physicist Christiaan Huygens developed the theory of wavefronts. When a wavefront of parallel light rays enters the interface between an optically denser material ( A) and an...