n1 sin q1 = n2 sin q2 Correct!


In this case n1 = 1.0, n2 = 1.5, q1 = 30°.

1 sin 30 = 1.5 sin q2
q2 = 0.5/1.5 = 0.333
q2 = 19.5°.

This is also the value of q3

Now evaluating q4

n2 sin q3 = n3 sin q4
1.5 sin 19.5 = 1.3 sin q4
sin q4 = (1.5)(0.333)/(1.3) = 0.385
q4 = 22.6°

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