What causes the magnification of visual images underwater?

The magnification of visual images underwater is primarily caused by the different refractive properties of air and water. When light travels from one medium to another, such as from air into water, it changes speed and direction, a phenomenon known as refraction.

In air, light travels faster and bends differently than it does in water due to the higher density of water compared to air. When an object is submerged in water, the bending of light makes the object appear larger than it actually is because the angles at which the light rays enter the eye are altered. This optical effect leads to a perceived magnification of underwater images compared to how they appear in air.

For instance, if an underwater object is viewed directly from above, it will look closer and larger than the same object would if viewed in air. Understanding this optical principle is essential for divers, as it impacts depth perception and the sizing of objects underwater.