Question

why is the speed of light is less in kerosine then water even when kerosine is a rarer substance then water?​

Answer 1

Answer:

• There are two terms namely optical density and physical density and both have different meaning.
• Density (physical quantity) deals with how closely molecules are packed in the material i.e., mass per unit volume and optical density deals with the retardation experienced by light as it transits through the medium. Optical density is also related to the refractive index of the material. Greater the optical density, higher is the refractive index. To put in other words, greater the optical density, greater is the retardation experiences by light in the material and this inturn translates to higher refractive index of the material.
• Their refractive indices being
• Kerosene 1.44
• Water 1.33
• and their densities being
• Kerosene (or paraffin) = 0.78-0.81 g/cm3
• Water = 1gm/cm3
• Since RI of kerosene is higher than water hence kerosene is more optically denser than water.
• Since water can pack more closely rather than kerosene, hence water is denser than kerosene.

Explanation: