Converging lens: what do we know about it?

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Converging lens: what do we know about it?
Converging lens: what do we know about it?
Anonim

As children, many of us played with a magnifying glass. It was quite interesting to observe how it can be used to burn through a newspaper, wood and other objects. As we get older, we often use magnification to zoom in on image details or small text. But how, in fact, it works, why in some cases the images are large, while in others they are upside down, not everyone knows. Let's figure out how a converging lens works, what its parameters mean, and what role the distance to the object in question plays.

converging lens
converging lens

Basic definitions and properties

Any theory is best broken down starting with key concepts. So, let's start with the fact that the types of lenses directly depend on their shapes. As a basis for their manufacture, both glass and other transparent materials with a high refractive index can be used. If the middle of the lens is thicker than its edges, then you get a converging lens, and otherwise - a divergent one. The straight line that passes through the centers of curvature of its two surfaces is the main optical axis. A diverging or converging lens is said to be thin if the radii of its sides are substantially greater than its thickness anywhere. If a beam of light passes through the center of the lens, it does not change its direction.

lens magnification
lens magnification

This property is often used to determine how the final image will turn out. But if a beam of rays parallel to its main optical axis hits the surface of the lens, then after they cross its optical center and pass the focal length, their paths will intersect at a common point, which is called the focus. The shorter the focal length, the greater the optical power of this optics. The last parameter is usually measured in diopters.

How to determine what image a converging lens will give?

All you have to do is find out what its focal length and distance to the subject are. Next, we simply compare them and follow the following rules:

  1. If an object is very, very far from the lens, we can assume that all the rays of light that are reflected from it are parallel to the main optical axis, which means that they all intersect in focus, and we simply will not see this object.
  2. If the object of observation is located behind a double point of focus, that is, behind a double focal length, then the image will be turned upside down. Moreover, its dimensions will be smaller than the dimensions of the object itself.
  3. When the subject is in the double focus point, its image will also be reversed. But this time, its dimensions will correspond to the dimensions of the object in question.
  4. types of lenses
    types of lenses
  5. If you zoom in a little further so that the object is halfway between focus and double focus, the image will remain inverted, but now it will be enlarged.
  6. A curious effect is obtained when the converging lens is exactly at the focal length of the subject. In this case, after refraction, the rays will go parallel to each other and we will not see the image.
  7. And only when the object is between the optical center and the focus, it will be possible to use the magnifying glass as we usually do. The resulting image will be upright and enlarged, allowing you to see all the smallest details in detail.

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