Difference between Concave and Convex Lens

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. A single piece of transparent material consists of a single lens. The composite lens consists of several simple lenses, which normally lie along a common axis.

The Lens, Based on its Shape, can be Divided into two Types as :

  • 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.


Convex Lens:

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. 


There are Three types of Convex Lens:

1) Biconvex lens.

2) Plano-convex lens.

3) Concavo-convex lens.

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

  1. 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.

  1. 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.

  1. 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.

  1. 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.


Concave Lens:

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 lens -

There are Three Types of the Concave Lens -

(i) Bi-Concave

(ii) Concavo Plano

(iii) Concavo Convex


Lenses as a Combination of Prisms                    

Derivation of Lens Formula

Its formula can be given as:

Where,

Focal length

The distance of the image from the centre

The distance of the object from the centre

Thus, the magnification of the image can be given by:

Where, 

Magnification of the lens

Height of image

Height of object


Uses of the Concave Lens:

  1. Eye Glasses :

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

  1. 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.

  1. 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.

  1. 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 artefacts that provide a wider view of objects outside the door.


Difference Between Convex and Concave Lenses :

Convex Lens

Concave 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.

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.

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

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

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

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

Use for correction of long-sightedness.

Use for correction of short-sightedness.

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

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

e.g. Human Eye, Camera, etc.

e.g. Lights, Flashlights,etc.