What does 'apparent depth' refer to in optics?

'Apparent depth' is a concept that refers to the perceived depth of an object when viewed through a medium, such as water or glass, due to the phenomenon of refraction. When light travels from one medium to another, its speed changes, causing the light rays to bend. This bending of light affects how we perceive the location of objects submerged in a different medium.

For example, when viewing a fish swimming in a pond, the fish appears to be at a shallower depth than it actually is. This discrepancy arises because the light rays coming from the fish bend as they pass from water into air, making the fish appear closer to the surface than it truly is. The amount of bending relies on the indices of refraction of the two media involved.

As a result, the effective depth seen by an observer is not the actual depth of the object, but rather a shallower depth that is influenced by the properties of the medium. This concept is critical in optics as it helps explain various visual phenomena and is important for applications in fields like photography, vision science, and even underwater navigation.