# Physics Lesson 12.9.1 - What Are Lenses? Types of Lenses

Welcome to our Physics lesson on What Are Lenses? Types of Lenses, this is the first lesson of our suite of physics lessons covering the topic of Lenses. Equation of Lenses. Image Formation of Lenses, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

## What Are Lenses? Types of Lenses

Lenses are optical tools used to enlarge or reduce the size of images. This is made possible through refraction occurring when light passes through them.

In a certain sense, lens is an extension of the concept of curved mirrors because unlike the latter, a lens can be used in both sides, as it is a piece of transparent material, usually circular in shape, with two polished surfaces, either or both of which is/are curved.

There are two main categories of lenses: converging (concave) and diverging (convex). They are shown in the figure below.

From the figure, you can see that a converging lens is thicker at middle and thinner in extremities, while diverging lenses are thinner at middle and thicker in extremities.

The lenses shown in the figure are both regular, i.e. they behave equally in both directions. However, there is a variety of lenses with non-identical sides. Some of them are shown in the figure below.

All lenses except plane-concave and plane-convex ones have two focîbecause they are formed by joining two spherical parts. As a result, they have two centres as well (one in each side). They can be at different distances from the lens depending on their curvature but for simplicity, we will only consider lenses that have identical sides, i.e. which have the same value for focîand centres in both directions, as shown in the figure below.

You have reached the end of Physics lesson 12.9.1 What Are Lenses? Types of Lenses. There are 8 lessons in this physics tutorial covering Lenses. Equation of Lenses. Image Formation of Lenses, you can access all the lessons from this tutorial below.

## More Lenses. Equation of Lenses. Image Formation of Lenses Lessons and Learning Resources

Optics Learning Material
Tutorial IDPhysics Tutorial TitleTutorialVideo
Tutorial
Revision
Notes
Revision
Questions
12.9Lenses. Equation of Lenses. Image Formation of Lenses
Lesson IDPhysics Lesson TitleLessonVideo
Lesson
12.9.1What Are Lenses? Types of Lenses
12.9.2Special Rays in Lenses
12.9.3Image Formation in Converging Lenses
12.9.4Image Formation in Diverging Lenses
12.9.5Equation of Lenses
12.9.6Magnification Produced by Lenses
12.9.7Aberration in Lenses
12.9.8Combined Systems of Lenses and Curved Mirrors

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