What is the physics behind reflections and why they appear opposite?

Question

What is the physics behind reflections and why they appear opposite?

Answer 1

The law of reflection states that the direction of incoming light (the incident ray), and the direction of outgoing light reflected (the reflected ray) make the same angle with respect to the surface normal, thus the angle of incidence equals the angle of reflection; this is commonly stated as θi = θr.

The law of reflection arises from diffraction of a plane wave (with small wavelength) on a flat boundary: when the boundary size is much larger than the wavelength then electrons of the boundary are seen oscillating exactly in phase only from one direction—the specular direction.

Answer 2

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