Question

Write the definition of refractive index of a medium.

Answer 1

Hint : The refractive index of a medium is a measure of the path of light in that medium. It is related to the velocity of light in the medium.

Complete step by step answer
The refractive index of a medium is defined as the ratio of speed of light in the vacuum or the free space to the speed of light in the medium. So it is given by
 $ \mu = \dfrac{c}{v} $
Here $ c $ is the speed of light in vacuum, approximately equal to $ 3 \times {10^8}m/s $ , and $ v $ is the speed of light in the medium.
The refraction index is a measure of the optical density of a medium. So it measures the bending of light rays when it travels from the vacuum to the medium. It is also defined from the Snell’s law as the ratio of the sine of angle of incidence to the sine of angle of refraction, that is,
 $ \mu = \dfrac{{\sin i}}{{\sin r}} $
Both the angle of incidence and angle of refraction are measured from the normal line passing through the interface of the two mediums.

Note
The refractive index of a medium is measured using an instrument called the Refractometer. The refractive index is used to measure the purity of a substance. It is also useful in optical instruments such as lenses, prisms, optical fibres etc. In an aqueous solution, it can be useful in the measurement of the concentration of the solute particles contained in it. Further, it is also used in measuring the apparent depth of an object under water, as seen by an observer outside.