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Difference Between Concave and Convex Lens

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Last updated date: 19th Jul 2024
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What is a Lens?

A lens is an optical tool that, by refraction, converges and diverges a light beam. It is an optical transmissive system that focuses or spreads a beam of light by refraction. Lenses are classified into two types called concave and convex.


Do you find any difference between the two? Well, there are various instances that make them different. Also, each lens type has its own nature of image formation and application that we will understand on this page. Along with this, we will get to learn how concave lenses are different from convex.


Also, we will understand the real-life applications of concave and convex with the help of everyday examples.


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Concave and Convex Lenses - Definition 


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  • Convex Lens

In a convex lens (sometimes called a positive lens), the glass (or plastic) surfaces bulge outwards at the centre. A convex lens is also called a converging lens because the parallel light rays moving through it curves inward and touches (converges) at a position just beyond the lens known as the focal point.

  • Concave Lens 

With external surfaces curving inside, a concave lens is just the opposite, making parallel light rays curve outwardly or diverge. Therefore concentric lenses are sometimes referred to as divergent lenses. The disparity between concave and convex lenses will clearly be understood when contemplating the concave lens internally.


Difference between Concave and Concave Lens


Parameters 

Concave Lens

Convex Lens

Nature of lens

On passing the light through the lens, it bends the light rays away from each other (i.e., it diverges the rays). So due to this, it is called a diverging lens.

On passing the light through the lens, it bends the light rays towards each other (i.e., it converges the rays). So due to this, it is called a converging lens

Thickness/thin

A concave lens is thicker at the edges and thinner at the centre.

A convex lens is thicker at the centre and thinner at the edges.

Image 


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Converging/Diverging

Due to the diverging rays, it is called a diverging lens.

Due to the converging rays, it is called a converging lens.

Use

Use for correction of short-sightedness.

Use for correction of long-sightedness.

Nature of focal length

It is also called a negative lens due to its negative focal length nature.


It is also called a positive lens due to its positive focal length nature.

Examples

Lights, Flashlights, etc

Human Eye, Camera, etc.


Now, let us understand in detail about concave and convex lenses along with their applications. 


What are Concave Lenses?

A Concave lens is a lens that diverges the straight light beam coming from the source to create a reduced, upright, or digital picture. It can generate real and virtual objects, depending on the light source. Convex lenses are known as positive lenses, plus lenses, lenses that converge and condensers. The convex lenses are in the middle fat and on the edges thin. 


Types of Concave Lenses

There are Three Types of the Concave Lens -


  • Bi-Concave


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Bi-Concave are also called double-concave lenses that have equal radius of curvature on both sides of the lens and function similarly to plano-concave lenses by causing collimated incident light to diverge.

  • Plano-Concave 


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A plano concave lens is an optical lens with one concave surface and one flat surface that has a negative focal length.

  • Concavo Convex

A concavo-convex lens has a convex face smaller curvature than the concave face, so that the former tends constantly away from the latter.


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Applications of Concave Lenses

  • Eye Glasses

The concave lens is used to treat the problem of near-sightedness or myopia by diverging the light ray and making a clear image of the object on the retina.

  • Camera

The picture enhancement in the frame is performed by introducing several lenses one after the other like a convex lens preceded by a concave lens followed by a convex shaped lens.

  • Flashlights

The concave lens is used to magnify the light created by the light beam, which raises the diameter of the beam by diverging the light ray from the hollow side to the other side, rendering the light ray broader and bigger.

  • Peepholes

Peepholes on doors provide a panoramic view of items on the other side of the door, acting as a safety device. Peepholes contain concave lenses to increase the proportion of artifacts that provide a wider view of objects outside the door.


What are Convex Lenses?

A convex lens is also known as a convergent lens. It is a lens which converges light rays passing parallel to its main axis. They can be identified by their shape. The upper and lower edges are relatively thin and the middle portion is thick. 


Types of Convex Lenses

Three Types of Convex Lens are as follows:

  • Biconvex lens


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Biconvex lenses are a simple lens comprising two convex spherical surfaces, generally with the same radius of curvature.

  • Plano-convex lens


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These lenses are positive focal length elements that have one spherical surface and one flat surface. They are designed for infinite conjugate (parallel light) use or simple imaging in non-critical applications.

  • Concavo-convex lens

Through a biconvex lens converges a beam of light from objects farther from its principal focus, a concavo convex lens is convex when seen from one side while it is concave from the other. As shown in this figure below:


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Uses of convex lens 

A convex lens is used for different purposes including glass enlargement, mirror, telescope, hypermetropia correction etc.


Applications of Convex Lenses

  • Magnifying glasses

The most general use of the convex lens is in magnifying glasses. In a magnifying glass, if an object is placed on one side of a convex lens closer to the focal point, the image of the object is formed on the same side as the object and is highly magnified. The angle subtended at the eye. The position of image and magnification produced will depend on the position of the object.

  • Eyeglasses

When the lenses of the eyes of an individual fail to clearly focus the light of the retina, it causes far-sightedness or near-sightedness problems. The convex lens is used for solving the long-sightedness or hypermetropia problem by bending the light ray that shortens the focal length and thus, properly focuses the light ray on the retina.

  • Cameras 

In the camera, the convex lens is used to focus and magnify the image. There are a number of lenses that are inserted where one concave lens is followed by a convex lens. The magnification of the image happens due to the convex-shaped front lens of the camera.

  • Microscopes

Modern microscopes involve more than just one set of lenses. They have an objective lens that sits near the object and an ocular lens that sits closer to your eye. These add to the object’s magnification. The lens of the eye part normally magnifies 10x, while 40x is magnified by a standard objective lens. In general, there are three types of lenses for microscopes. The end lens results in a magnified or reversed image of these three.


From the above text on the difference between concave and convex lenses, we understand that convex lenses focus distant images at a point on the side of the lens opposite from a light source, while concave lenses focus distant objects on the side of the lens that lie opposite to the incidence light is, sees the object as to be at a point behind the lens.