For the same angle of incidence in medium P, Q and R, the angles refraction are 
, 
and 
respectively. In which medium will the velocity of light be minimum? Give reason for your answer.
Refractive index, 
……(1)
Hence refractive index of a medium is inversely proportional to the speed of light in that medium.
Also μ = 
…………….. (2)
⇒ Refractive index is inversely proportional to the angle of refraction.
From (1) and (2)
Velocity of light is directly proportional to the angle of refraction.
Thus velocity of light is minimum in medium R because angle of refraction is 150 is minimum.
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