If a scuba diver is underwater and looks up, he or she will see a round "hole" directly above him or her at the surface of the water. The rest of the surface will look like a mirror. Explain this phenomenon
snell's law
light coming from right above comes straight down to the diver.
however
light coming from near the horizon hitting beyond the critical angle just reflects back up to the sky.
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The phenomenon you are referring to is known as the "Snell's window" or the "subsurface horizon." When a scuba diver looks up from underwater, they might observe a round "hole" directly above them at the surface of the water, while the rest of the surface appears like a mirror or reflects the surrounding environment.
This optical effect occurs due to the difference in refractive indexes between air and water. Refractive index is a property that measures the bending of light as it passes through different substances. When light passes from air into water, it changes direction and speed, causing it to bend.
In the case of the scuba diver looking up, the light rays coming from the surrounding objects above the water's surface enter the water. As they approach the water's surface at an angle, they transition from water into air. This transition causes the light rays to bend in a way that they converge towards a specific angle - called the critical angle.
At the critical angle, the light rays are refracted to the point where they travel parallel to the water's surface. This results in a circular patch of the surface appearing brighter and clear, like a window. This circular area is what the diver sees as the round "hole" above them.
Outside of this circular area, the refraction of light becomes less pronounced, and the surface of the water acts as a mirror, reflecting the surrounding environment. The diver perceives the rest of the surface to be mirrored because the incoming light rays from the objects are no longer reaching their eyes directly, but are being reflected off the water's surface.
It's important to note that the size and visibility of the Snell's window can be influenced by factors such as water clarity, the angle of observation, and the amount of sunlight reaching the water's surface. Nonetheless, it remains a fascinating phenomenon for scuba divers to observe and contemplate while exploring the underwater world.