# . State the laws of refraction of light. Explain the term absolute refractive index of a medium and

write   an expression to relate it with  the speed  of light in vacuum

Ans. Laws of Refraction:

(i) The first law of refraction of light states that the incident  ray, the refracted  ray and  the normal at the point of incidence, all lie in the same plane

(ii) The second law of refraction of light is the Snell's  Law of Refraction. It states that the ratio of sine of the angle of incidence to the sine of angle of refraction is a constant  for a given pair of medium.

sin i /sin r = constant

This constant (n) is called refractive  index  of the medium.

i. When the light is going from  vacuum  to another  medium,  then  the value  of refractive index is called  the absolute  refractive index.

ii.The ratio of speed of light in vacuum to the speed of light in a medium is called the absolute  refractive index of that medium,  i.e.,

Absolute refractive index (of a medium) = Speed of llight in vaccum (c) / Speed of light in medium (v)