Final answer:
Objects appear shallower in water and legs shorter in a pool due to the refraction of light, which happens as light travels from water to air, bending away from the normal due to different refractive indices. Misjudging depth can lead to injuries when diving.
Step-by-step explanation:
Refraction and Perception in Water
When an object is submerged in water, it appears to be at a shallower depth than it actually is. This is due to the refraction of light as it passes from water to air. Refraction is the bending of light when it moves between mediums with different refractive indices. Water has a higher refractive index than air, so light rays bend away from the normal (an imaginary line perpendicular to the interface between the two mediums) as they exit the water, making the object seem closer to the surface than it truly is.
People sometimes sustain neck and spinal injuries when diving into unfamiliar bodies of water because they misjudge the depth due to this optical illusion. Diving into what appears to be deep water can be deceptive, leading to collisions with the bottom of the water body.
Additionally, a person's legs may appear shorter when wading in a pool because the light rays from their legs bend upon exiting the water, altering the perceived image position. Here is a simple ray diagram:
- Draw the observer outside the water, with their eye level at the assumed water level.
- Represent the person's legs submerged in water.
- Draw the path of rays from the feet upwards, bending at the water-air interface towards the observer's eye.
The rays bend at the surface of the water due to refraction, and the observer sees an image that is vertically compressed, making legs appear shorter.