The law of reflection tell us:
The angle of incidence equals the angle of reflection.
If you change the orientation of the mirror by angle X,
the angle of incident and the angle of reflection will both change X.
So, the angle of the reflected ray changes by 2X.
You can drag the light source(with mouse) to change the incident angle,too. :)
Virtual Physics laboratory Original URL
Fu-Kwun Hwang, Dept. Of Physics, National Taiwan Normal University.