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2020 Phase-2 Ray Optics and Optical Instruments Total internal reflection - critical angle and refractive index Medium Question 30 of 89 in Ray Optics and Optical Instruments

If the critical angle for total internal reflection from a medium to vacuum is $45^\circ$, then velocity of light in the medium is,

A $3\times10^8$ m/s

B $1.5\times10^8$ m/s

C $\dfrac{3\times10^8}{\sqrt2}$ m/s

D $\sqrt2\times10^8$ m/s

The answer is C.

Solution

Refractive index $\mu=\dfrac{1}{\sin\theta_c}=\dfrac{1}{\sin45^\circ}=\sqrt2$. $v=\dfrac{c}{\mu}=\dfrac{3\times10^8}{\sqrt2}$ m/s.

Concept Total internal reflection - critical angle and refractive index

Ray Optics and Optical Instruments in past papers

89 questions from this chapter have appeared across 25 exam years.