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