Question

# A light wave enters from I medium into II medium. Its velocity in second medium is double that in I medium. For the phenomenon of total internal reflection to take place the angle of incidence must be greater than a certain value. This value is

A
20o
B
30o
C
45o
D
60o

Solution

## The correct option is B $$30^o$$Since velocity of light wave is inversely proportional to refractive index of medium. So the refractive index of second medium is half of the medium 1.$$\eta_1=2\eta_2$$  For total internal reflection the incident rays from denser medium should begreater than critical angle,$$\eta_1 sin\theta_c=\eta_2=\dfrac{\eta_1}{2}$$ So $$sin \theta_c = 0.5$$So $$\theta_c=30^o$$Physics

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