# Why the water acts like a mirror from the air?

Why the ray of light what is in the air (n = 1) is reflected in the water (n = 1.33) surface, and acts like a mirror?

The Snell law say what the ray is refracted deflected closer to the normal. Then there will never be any reflection (total internal), then not can work like a mirror. The critical angle is $$\arcsin(n_2/n_1)$$ where $$n_2 as you are going from the water to the air. This is the angel of 'total internal reflection'. On the other hand, the Brewster angle is $$\arctan(n_2/n_1)$$ where $$n_2>n_1$$ as you are going from the air to the water. This is the angle of perfect separation between polarizations. Light polarized perpendicular to the plane will be mostly reflected and light polarized in-plane will be completely refracted. When you combine these two concepts it means light from low angles beneath the water will never reach you (total internal reflection) and light from low angles above the water which enters the water will rarely reach you (subcritical polarization). That is why at low angles the light you see appears to be coming from above the surface. If you want an introductory mathematical answer, Wikipedia the 'Fresnel Equations'.