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# Find angle $\theta_a$ made by light ray when it gets refracted from water to air as shown .

$(a)\;\sin ^{-1} (4/5) \\ (b)\;\sin ^{-1} (3/5) \\ (c)\;\sin ^{-1} (4/3) \\ (d)\;\sin ^{-1} (3/4)$

Snell's law $\mu_ w \sin \theta_w=\mu _a \sin \theta _a$
$\large\frac{4}{3} \times \frac{3}{5}$$=1 \sin \theta_a$
$\sin \theta_a =\large\frac{4}{5}$
$\theta_a =\sin ^{-1} \large\frac{4}{5}$
Hence a is the correct answer.

edited Jul 28, 2014