Have you ever sat at the bottom of a swimming pool and thought about the ceiling covered in water? Most of the surface is light blue and you can’t see through it even when the water is clear. But directly above you is a clear round window.
And here’s the cool thing: The ring gives you a fisheye view so you can see not only the sky, but also things around your pool, like the trees and people sipping Mai Tais on the pool deck. This cool effect is caused by the optical properties of water, and it has a name: the Snell window.
You don’t even need to spend much time underwater to see this phenomenon. Maybe, like me, you love watching spearfishing videos on YouTube. Here’s a beautiful example of a Snell window from the YBS Youngbloods channel (clicking the link will take you directly to the interesting 15 seconds):
One interesting thing to note is that the size of the window seems to stay the same as the diver (Brody) and cameraman descend. You might be wondering what that changes. Think about it: if you were to back away from a window in your home and film it, the window would appear smaller.
In fact, the Snell window big—See how the divers on the surface are filling up the water more and more? But unlike windows on land and other things, Angular The size seen by the eye remains the same regardless of distance.
The mysteries of the deep sea! There is beautiful physics behind it. Let’s find out.
Refraction and Snell’s Law
Unlike sound, light is an electromagnetic wave and does not require a medium to “travel”. This means that, fortunately for us, it can travel through space just like sunlight. Light travels at a speed of 3 x 10, so8 meters per second, so this journey from the Sun to the Earth takes about 8 minutes.
But when light enters a transparent medium like air, something happens: light slows down. Air slows the speed of light by just 0.029 percent, but when light enters water, it slows down by about 25 percent, just like how light slows down when running from the beach into the ocean because water is denser than air.
This velocity difference varies depending on the medium, and the refractive index (yeah) is the ratio of the speed of light in a vacuum to the speed of light in a particular material. The higher the refractive index, the slower light travels through that medium. In air, yeah = 1.00027. In water, yeah = 1.333. For glass, yeah = 1.5
But when you change the speed, direction Refraction of light means changing the direction of light. This is actually what “refraction” means. If you put a straw in a glass of water, you will notice that the part of the straw below the water level does not match the part above the water level. Why? Because the light from the underwater part is bent, it appears to be in a place that is not actually there.
