In this diagram, medium A represents water and medium B represents air. The phenomenon in this diagram, moving from A to B, is called

In this diagram, the phenomenon moving from medium A which represents water to medium B that represents air is called refraction.

Explanation:

Refraction takes place when light passes through a water surface due to its refractive index which is 1.33. Air possesses a refractive index of about 1. Looking at the phenomenon moving between medium A and B, it seems to bend at the water's surface. This happens because of the bending of the light rays as they move from the water to the air. The time when the rays reach the eyes, the eyes trace them back as straight lines or lines of sight. These lines divide at a higher position than where the actual rays originated. This causes the phenomenon to appear higher and the water to appear shallower than what it is in reality.