there is a special incident ray that reflects right back to itself   how would you aim this incident ray to achieve that effect ? what is the angle of incidence of this incident ray/ 

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When light rays reflect, the angle of incidence (the angle from which the ray is different from the normal of the surface, or the imaginary line coming straight out of the surface) is equal to the angle of reflection (which is again, the difference between the normal and the reflected angle).

In order to have an incident ray rebound on itself, the incident ray needs to be parallel to the surface normal. At this point, the angle of incidence is zero. Thus, the angle of reflection is also zero.

To achieve this, you would need to aim the ray of light directly at the surface, along its normal. This means you need to point it directly at the object, without any angle.

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