Spherical lenses: types, characteristics and uses .Spherical lenses are present in everyday life in different ways, mainly in the manufacture and operation of glasses, which provides greater quality of vision for millions of human beings around the globe.
Physics is the science dedicated to the study of these lenses, so that it understands the behavior of light rays when they cross these screens. This article seeks to summarize the main information, types of lenses, characteristics and how they are used in everyday life: read and find out more!
What are lenses?
Lenses are objects that have the ability to reflect and refract light rays. When light falls on a lens, it is possible that the path of the light beams is changed, so the images can be enlarged or reduced, when compared to reality.
In general, they are made of transparent materials, such as glass and acrylic. There must be homogeneity in this material, which provides better transmission of light rays along their path.
Spherical lenses, specifically, may have edges thicker than the center, which are concave or converging lenses. Or they may have edges thinner than the center, which are called convex or divergent. This changes the way light rays travel and cross the surface.
Thus, each type of lens will form different images for the same object. This aspect also changes depending on the refractive index of the material that makes up the lens, the material in which it is immersed (water or air, for example), and it is also possible to understand whether the image formed is virtual or real, depending on physical studies.
Types of spherical lenses
Concave, or divergent, spherical lenses have the ability to refract light rays in a way that separates their trajectories. The shape observed externally is characterized by thick edges with a sharper center, as if the optical screen was “hollowed out”, and this perception can be a trick to remember that concave lenses are hollowed out . As a result, they will be represented by a vertical bar with inverted triangles at the ends.
Even though the front part of the lens is concave, it is also necessary to observe the back part to understand the true path of the light rays. Therefore, diverging lenses can have the posterior surface in the following way:
- Concave, so the two parts are hollow and will be called biconcave;
- Flat, and will be called plano-concave; or
- Convex, to form a convex-concave system.
Spherical convex lenses are also called converging lenses. The word refers to the convergence of rays to the same point, as if they were “scattered” and then gathered towards a specific location in space.
When observing this type of screen, one notices that the edges are thinner than the center, which gives the impression of a small “hill”, an elevation in the central part of the lens. Given these characteristics, they are represented by a vertical line with arrows pointing outwards: ↕.
If at least one face of the lens is convex, it is possible that the other part is:
- also convex, so as to be called biconvex;
- concave, with a “half moon” shape, which is called concavo-convex; or
- plane, and will be called plano-convex.
In general, convex lenses are useful for magnifying objects. Its most common use is for people with ophthalmological difficulties, especially difficulty seeing close objects — which can be something developed at a young age and will be called hyperopia, or a natural process of ocular aging, which is presbyopia.
Focusing ability of spherical lenses
The behavior of light rays in a spherical lens can be observed numerically, to understand the ability of that system to converge or diverge any ray of light. To do this, a formula is used that summarizes the power (P) of the lens:
P = 1/f
P = focal power, measured in the unit of Diopters (D)
f = focal length (distance between the lens and the focus, measured in meters)
When the lenses are converging, their focal power will have a positive value. Conversely, divergent or concave lenses will have a negative diopter value, with P<0.
Uses of spherical lenses
As already mentioned, the main use of spherical lenses is to enlarge or reduce visual objects to improve the visual acuity of patients with eye difficulties.
The idea is based on the anatomy and physiology of the eyeball: light rays are expected to cross the cornea, enter the optical system and fall directly on the retina, which processes information through specialized nerve cells and sends the data to be interpreted in the eyeball. brain.
In the case of myopes, the difficulty consists in looking into the distance, justified by an anatomical focal incidence before the retina. Therefore, it is necessary to use a correct degree of negative diopters, which allow a divergence of the rays, which “pushes” the focus of the lens backwards, so that it also focuses on the retina.
Other common uses for spherical lenses are related to science, for example the use of magnifying lenses to observe objects and living beings under microscopes. It is these optical systems that allow the understanding of cellular structures and their organization, for example.