Club Science

Convex lens is thicker at the centre and thinner at the edges.

An optical lens is generally made up of two spherical surfaces. If those surfaces are bent outwards, the lens is called a biconvex lens or simply convex lens. These type of lenses can converge a beam of light coming from outside and focus it to a point on the other side. This point is known as the focus and the distance between the centre of the lens to the focus is called the focal length of convex lens. However, if one of the surfaces is flat and the other convex, then it is called a plano-convex lens.

Difference between convex and concave lens:

There is another type of lens known as concave lens. The major differences between the two are:

CONVEX	CONCAVE
This lens converges a straight beam of light.	This lens diverges a straight beam of light.
This lens is thicker at the centre and gets thinner as we move towards the edges.	This lens is thinner at the centre and gets thicker as we move towards the edges.

A concave lens will always produce diminished, upright and virtual image of the object in front of it. But the nature of the image produced by a these lens depends upon the position of the object. It can form both real and virtual images depending on where the light is coming from.

Uses of convex lens

These are used for a variety of purposes in our day to day lives. For example,

The lens in the human eyes is the prime example. So the most common use of the lens is that it helps us to see.

Another common example of the use of this type of lens is a magnifying glass. When an object is placed in front of it at a distance shorter than the focal length of the lens, it produces a magnified and erect image of the object on the same side as the object itself.
It is used to correct Hypermetropia or long-sightedness.
It is used in cameras because it focuses light and produces a clear and crisp image.
More generally these are often used in compound lenses used in various instruments such as magnifying devices like microscopes, telescopes and camera lenses.
A simple kind of these lenses can focus light into an image, but that image won’t be of a high quality. For correcting the distortions and aberrations, it is better to combine both types of lenses.
Image Formation by Convex Lens

There are six possibilities of position of object in the case of convex lens:
- Object at infinity
- Object beyond centre of curvature, C
- Object at centre of curvature, C
- Object between centre of curvature, C and principal focus, F
- Object at principal focus, F
- Object between principal focus, F and optical centre, O
Object at infinity:

Convex lens converge parallel rays coming from objet at infinity and a highly diminished - point sized, real and inverted image is formed at principal focus F2.

Fig: Object at Infinity

Properties of Image: Image is highly diminished, real and inverted.

Object beyond centre of curvature, C1 or 2F1:

A diminished, real and inverted image is formed between principal focus, F2 and centre of curvature, C2 at the opposite side when an object is placed beyond C1 of a convex lens.

Fig: Object Beyond 2F

Properties of Image: Image is diminished, real and inverted.

Object at centre of curvature, C1 or 2F1:

A same sized, real and inverted image is formed at centre of curvature, C2 when object is placed at centre of curvature, C1 of a convex lens.

Fig: Object at 2F

Properties of Image: Image is same size as object, real and inverted.

Object between centre of curvature, C1 and principal focus, F1:

An enlarged, real and inverted image is formed beyond centre of curvature, C2 when an object is placed between centre of curvature, C1 and principal focus, F1 of a convex lens.

Fig: Object between 2F and F

Properties of Image: Image is enlarged, real and inverted.

Object at principal focus, F1:

An infinitely large, real and inverted image is formed at infinity when object is placed at principal focus, F1 of a convex lens.

Fig: Object at F

Properties of Image: Image is highly enlarged, real and inverted.

Between principal focus, F1 and optical centre, O:

A virtual, erect and enlarged image is formed at the same side of lens, when an object is placed between principal focus, F1 and optical centre, O of a convex lens.

Fig: Object between F and O

Properties of Image: Image is enlarged, virtual and erect.