question_answer

The inner surface of a cone coated by a reflecting layer forms a conical mirror. A thin incandescent filament is stretched in the cone along its axis. Determine the minimum angle a of the cone for which the rays emitted by the filament will be reflected from the conical surface not more than once

A) \[120{}^\circ \]

B) \[90{}^\circ ~~\]

C) \[150{}^\circ \]

D) \[135{}^\circ \]