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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 focal length of the lens of a camera is \(38.0 \mathrm{~mm}\). How far must the lens be moved to change focus from a person \(30.0 \mathrm{~m}\) away to one that is \(5.00 \mathrm{~m}\) away?

What is the focal length of a magnifying glass if a \(1.0-\mathrm{mm}\) object appears to be \(10 . \mathrm{mm} ?\)

An object is moved from a distance of \(30 \mathrm{~cm}\) to a distance of \(10 \mathrm{~cm}\) in front of a converging lens of focal length \(20 \mathrm{~cm}\). What happens to the image? a) Image goes from real and upright to real and inverted. b) Image goes from virtual and upright to real and inverted. c) Image goes from virtual and inverted to real and upright. d) Image goes from real and inverted to virtual and upright. e) None of the above.

A person with a near-point distance of \(24.0 \mathrm{~cm}\) finds that a magnifying glass gives an angular magnification that is 1.25 times larger when the image of the magnifier is at the near point than when the image is at infinity. What is the focal length of the magnifying glass?

Where is the image formed if an object is placed \(25 \mathrm{~cm}\) from the eye of a nearsighted person. What kind of a corrective lens should the person wear? a) Behind the retina. Converging lenses. b) Behind the retina. Diverging lenses. c) In front of the retina. Converging lenses. d) In front of the retina. Diverging lenses.
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