The velocity of light in a medium is 1.5 $\times$ 108 ms−1. The critical angle C for a ray going from the medium into air is ______.

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The velocity of light in a medium is 1.5 $\times$ 108 ms−1. The critical angle C for a ray going from the medium into air is $30^\circ$. Explanation: Given: Velocity of light in medium, v = 1.5 $\times$ 108 m/s Velocity of light in air, c = 3 $\times$ 108 m/s The refractive index (n) of the medium relative to air is: n = c/v = (3 xx 10^8)/(1.5 xx 10^8) = 2 The critical angle (C) is given by: sin C = 1/n = $\frac{1}{2}$ = 0.5 C = sin−1 (0.5) = $30^\circ$

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