Q20 of 56 Page 1

With the help of a ray diagram, state what is meant by refraction of light. State Snell's law for refraction of light and also express it mathematically.

The refractive index of air with respect to glass is 2/3 and the refractive index of water with respect to air is 4/3. If the speed of light in glass is 2x108 m/s, find the speed of light in (a) air, (b) water.

Refraction of light is defined as the bending of light when the light ray passes from one medium to another.


Snell’s law of refraction states that: the ratio of Sine of the angle of incidence to the sine of refraction is constant for a given pair of media. It establishes a relation between angle of incidence and angle of refraction.


It can be expressed mathematically as follows:



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Given: The refractive index of air with respect to glass is = 2/3


Refractive index of water with respect to air = 4/3.


Speed of light in glass = 2x108 m/s


Refractive index of air with respect to glass nag




Va = 2x108 m/s


(ii) Refractive index of water w.r.t air = 4/3


nwa =



On calculating we get velocity of light in water=2.25x108 m/s


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