Question

The following table gives the values of refractive indices of a few media.

S.No.	1	2	3	4	5
Medium	Water	Crown Glass	Rock salt	Ruby	Diamond
Refractive index	1.33	1.52	1.54	1.71	2.42

Use this table to give an example of (i) a medium pair so that light speeds up when it goes from one of these media to another (ii) a medium pair so that lights slows down when it goes from one of these media to another.​

Answer 1

Speed of light increases when it travels from denser to rarer medium and it decreases when it travels from rarer to denser medium. Because in a denser medium more particles get in the way. Any medium with a greater value of the refractive index is an optically denser medium with respect to a medium with a smaller value of the refractive index.

(i) If we take a pair of Diamond and crown glass, then the crown glass is rarer medium with respect to the diamond as it has a less refractive index as compared to diamond. Now if light travels from diamond into the crown glass, it would speed up as it has to travel through a less dense medium.

(ii) If we take a pair of water and crown glass, then the crown glass is denser than the water as it has a more refractive index as compared to water, so the speed of the light would decrease if it travels into crown glass from the water.