1.State the law of refraction of …

2.The refractive index of a medium is defined as the ratio of velocity of light in first medium to the velocity of light in that medium.

Mathematically refractive index {tex} [\eta]\ =\frac{v_{1}} { v_{2}}{/tex}

{tex}v_{1} {/tex} is the velocity of light in first medium.

{tex}v_{2}{/tex}  is the velocity of light in second medium i.e the medium under consideration.

Let the first medium is space or vacuum.

Now, the velocity of light in first medium will be c where c is the velocity of light.

Now, the refractive index {tex} \eta\ =\frac{c}{v}{/tex}

v is the velocity of light in second medium i.e medium under consideration.

Now the refractive index obtained is called absolute refractive index.

Hence, the absolute refractive index of a medium is defined as the ratio of the velocity of light in air to the velocity of light in that medium.

Mathematically  the absolute refractive index =

                                              {tex} \eta\ =\frac{velocity\ of\ in\ light\ air}{velocity\ of\ light\ in\ medium}{/tex}