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Chapter 31: Problem 14

The refractive index of the human cornea is about \(1.4 .\) If you can see clearly in air, why can't you see clearly underwater? Why do goggles help?

Short Answer

Expert verified
Underwater, your eyes cannot bend the light rays enough to focus them onto the retina, due to the similar refractive indices of water and the cornea, causing images to appear blurry. Goggles help by providing a layer of air in front of your eyes, which drastically changes the refractive index from water to air and allows your eyes to correctly refract the light rays for clear images.

Step by step solution

01

Understanding Refraction and Refractive Index

Refraction occurs when light passes from one transparent medium to another. This change of medium also alters the speed at which light travels. The refractive index measures how much light bends, or refracts, when entering a substance. The refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in the medium. For the human cornea, this refractive index is given as 1.4.
02

Observing Underwater

When you try to see underwater without goggles, the water comes into direct contact with your eyes. The refractive index of water is about 1.33, which is very close to the refractive index of the human cornea (1.4). This closeness in refractive indices means that light rays entering your eyes from the water do not get significantly refracted or bent - so your eyes can't focus the light correctly. As a result, underwater images appear blurry.
03

The Role of Goggles

Goggles provide a layer of air in front of eyes. When you wear goggles, light rays from the underwater object first pass through the water, then the air in the goggles, and finally the cornea into your eye. Now, because the refractive indices of air (approximately 1) and the cornea (1.4) differ significantly, light rays refract enough to provide a clear image.

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Most popular questions from this chapter

Show that placing a 1 -diopter lens in front of a 2 -diopter lens gives the equivalent of a single 3 -diopter lens (i.e., the powers of closely spaced lenses add).

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