A light beam incident normally on the face AB is totally reflected to reach the face BC, if
A) \[2/3<\sin \theta <8/9\]
B) \[\sin \theta \le 2/3\]
C) \[\cos \theta \ge 8/9\]
D) \[\sin \theta >8/9\]
E) \[\cos \theta \le 8/9\]
Correct Answer: D
Solution :
Given \[{{\mu }_{g}}=\frac{9}{8}\] We know that\[\sin C=\frac{1}{_{w}{{\mu }_{g}}}\] \[\sin C=\frac{8}{9}\] \[C={{\sin }^{-1}}\left( \frac{8}{9} \right)\] \[\theta >{{\sin }^{-1}}\frac{8}{9}\]
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