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Chapter 33: Problem 16

Is it possible to start a fire by focusing the light of the Sun with ordinary eyeglasses? How, or why not?

Short Answer

Expert verified
Answer: Although eyeglasses with convex lenses can theoretically focus sunlight, it is highly unlikely that ordinary eyeglasses could generate enough heat to start a fire due to their primary function, design, small size, and varying thicknesses related to vision correction.

Step by step solution

01

Introduction to light focusing and heat generation

To start a fire, we need to generate enough heat to raise the temperature of the material to its ignition point. Focusing sunlight to a small spot can create intense heat by concentrating the sun's energy into a smaller area. A lens can help us focus light by bending the light rays that pass through it. The ability of a lens to focus light depends on its shape and material.
02

Types of lenses in eyeglasses

Eyeglasses usually have one of two types of lenses: convex lenses or concave lenses. Convex lenses are thicker in the center and thinner at the edges, and they can converge the light rays passing through them to a single point called the focal point. Concave lenses, on the other hand, are thinner at the center and thicker at the edges, and they diverge light rays away from each other.
03

Determining if eyeglasses can focus sunlight

To know if eyeglasses can focus sunlight, we first need to determine the type of lens they have. If the eyeglasses have convex lenses, they can potentially focus sunlight to a single point and generate heat. However, if the eyeglasses have concave lenses, they will not be able to focus sunlight and, thus, cannot generate enough heat to start a fire.
04

Evaluating the ability of eyeglasses to start a fire

Even if the eyeglasses have convex lenses capable of focusing light, we need to consider the quality and size of the lenses. The lenses in eyeglasses are designed primarily for vision correction and not for focusing sunlight. The size of the lenses is relatively small to be attached to a frame that a person can comfortably wear on their face. Moreover, eyeglasses lenses have varying thicknesses due to the prescription which may affect their ability to effectively focus light to a single point.
05

Conclusion

While it may be theoretically possible for eyeglasses with convex lenses to focus sunlight, due to their primary function and design, it is highly unlikely that ordinary eyeglasses could generate enough heat to start a fire. This is because the lenses are relatively small and have varying thicknesses to address vision problems, making them ineffective in focusing sunlight to a sufficiently small and intense enough spot to generate the required heat for starting a fire.

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Most popular questions from this chapter

The typical length of a human eyeball is \(2.50 \mathrm{~cm} .\) a) What is the effective focal length of the two-lens system made from a normal person's cornea and lens when viewing objects far away? b) What is the effective focal length for viewing objects at the near point?

What would you expect to happen to the magnitude of the power of a lens when it is placed in water \((n=1.33) ?\) a) It would increase. d) It would depend if the b) It would decrease. lens was converging or c) It would stay the same. diverging.

Three converging lenses of focal length \(5.0 \mathrm{~cm}\) are arranged with a spacing of \(2.0 \cdot 10^{1} \mathrm{~cm}\) between them, and are used to image an insect \(2.0 \cdot 10^{1} \mathrm{~cm}\) away. a) Where is the image? b) Is it real or virtual? c) Is it upright or inverted?

When a diver with \(20 / 20\) vision removes her mask underwater, her vision becomes blurry. Why is this the case? Does the diver become nearsighted (eye lens focuses in front of retina) or farsighted (eye lens focuses behind retina)? As the index of refraction of the medium approaches that of the lens, where does the object get imaged? Typically, the index of refraction for water is 1.33 , while the index of refraction for the lens in a human eye is \(1.40 .\)

The radius of curvature for the outer part of the cornea is \(8.0 \mathrm{~mm}\), the inner portion is relatively flat. If the index of refraction of the cornea and the aqueous humor is 1.34: a) Find the power of the cornea. b) If the combination of the lens and the cornea has a power of \(50 .\) diopter, find the power of the lens (assume the two are touching).
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