Observer the figure. Light falling on two different media are shown.

(a) Which medium has greater optical density?

(b) Why?

(c) Which medium has a greater refractive index?

(a) Medium 1 has greater optical density .

(b) In both the diagram ray is coming from the same medium i.e. air also angle of incident is same. In first case angle of refraction is 20⁰ and in diagram 2^nd angle of refraction is 30⁰ so derivation of light is more in medium 1 than in medium 2.So more the derivation of light greater the optical density.

(c) Medium 1 has greater index than medium 2.

Optical density of a medium 1 is greater than medium 2 so the speed of light in medium 1 will be slower than the speed of light in medium 2. Slower the speed indicates more the value of refractive index.

Many students get confused in optical density and physical density here optical density mean how fast or how slow light propagates through a medium where as physical density means how much lighter or heavier the object is when measuring with respect to water.