A ray of light enters a diamond from air. If the refractive index of diamond is 2.42, what % (percentage) is speed of light in diamond with that of speed in air?
Refractive index (μ) = 
Given μ = 2.42, c = 3 × 108.
Putting the value in the above formula, we get
⇒ 
⇒ 
⇒ v = 1.23 × 108 m/s.
Speed of light in diamond is 1.23 × 108 m/s
% of speed in diamond = 
= 41%
Thus there is 41% decrease in the speed of light in diamond than in air.
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