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Chapter 31: Problem 12

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
One cannot see clearly underwater because the refractive index of water, which is approximately 1.33, is closer to that of the cornea (1.4). Water doesn't bend the light as much as air does when entering the cornea, causing the light to not focus properly on the retina and thus resulting in a blurry vision. Goggles aid in maintaining clear vision as they contain air, so the light goes from water to air, and then to cornea, restoring the conditions similar to viewing in air, and ultimately leading to a clear focus on the retina.

Step by step solution

01

Understanding the Refractive Index and Vision

The normal vision of a human depends on the refractive index of the cornea, which is approximately 1.4, and the refractive index of air, which is approximately 1. When light enters the human eye, it moves from air to cornea; the difference in refractive indices helps the cornea to bend or refract the light onto the lens, which then focuses these rays onto the retina to form a clear image.
02

Seeing Underwater

When a person tries to see underwater, light moves from water to the cornea. The refractive index of water is about 1.33, which is closer to that of the cornea (1.4). Therefore, the water-cornea system doesn't refract light as effectively as the air-cornea system, causing light to not focus properly on the retina. This results in a blurry vision.
03

Role of Goggles

When a person wears goggles while swimming, there is a layer of air between the eyes and the water. So, the light entering the eyes goes from water to air, and then from air to the cornea. The transition from water to air creates a similar condition to seeing clearly in air, as the refractive index of air (1) varies more from the cornea's refractive index (1.4) than water does. This difference in refractive indexes assists the light to bend properly onto the retina, leading to an effective focus and clear vision.

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Most popular questions from this chapter

The cornea of the human eye has refractive index \(1.38,\) while the eye's lens has a graduated index in the range 1.38 to \(1.40 ;\) use 1.39 for this problem. For the aqueous humor between cornea and lens, \(n=1.34 .\) Find the angle through which light is deflected at the first surface of (a) the cornea and (b) the lens, if it's incident at \(20^{\circ}\) to the normal at each surface. Your result shows that the cornea is the dominant refractive element in the eye.

If you're handed a converging lens, what can you do to estimate its focal length quickly?

A contact lens prescription calls for +2.25 -diopter lenses with inner curvature radius \(8.6 \mathrm{mm}\) to fit the patient's cornea. (a) If the lenses are plastic with \(n=1.56,\) what should be the outer curvature radius? (b) With these lenses, the patient comfortably reads a newspaper \(30 \mathrm{cm}\) from her eyes. Where's the image as viewed through the lenses?

Show that identical objects placed equal distances on either side of the focal point of a concave mirror or converging lens produce images of equal size. Are the images of the same type?

Is there any limit to the temperature you can achieve by focusing sunlight? (Hint: Think about the second law of thermodynamics.)
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