Question

Explain the following:

Why does a water tank completely filled with water, when seen obliquely from above appear shallow?

Answer 1

Light rays from the bottom of the tank refract as they pass from water (optically denser) into air (optically rarer), bending away from the normal. The eye traces these rays backwards in straight lines, so they appear to come from a point above the actual bottom. Therefore, the bottom appears raised and the tank appears shallow.