A plane mirror lies face up , making an angle of 18 degree with the horizontal . A ray of light shines down vertically on the mirror.
What must be the inclination (to the horizontal) of the incident ray so that the reflected ray may be horizontal?
(show steps please )

Question

A plane mirror lies face up , making an angle of 18 degree with the horizontal . A ray of light shines down vertically on the mirror.
What must be the inclination (to the horizontal) of the incident ray so that the reflected ray may be horizontal?
(show steps please )

anonymous · Answer

In  drawing this and using the fact that the angle of incidence must equal the angle of reflection, I found that the incoming ray needs to be at twice the angle to the horizontal that the mirror is at 2 x 18 =36 o. Haven't proven it.