question_answer

One face AC of the glass prism is silvered as shown and the principal section of a glass prism is an isosceles triangle ABC with AB=AC. The ABAC, if the ray incident normally on the face AB and after two reflections, it energies from the base BC. perpendicular to it, is:

A) \[70{}^\circ \]

B) \[36{}^\circ \]

C) \[72{}^\circ \]                                   

D) \[44{}^\circ \]

Correct Answer: B

Solution :

                 \[\alpha +2\beta ={{180}^{o}}\] and       \[\beta =2\alpha \] \[\alpha ={{36}^{o}}\]