Difference between Convex and Concave lenses - Future Study Point

# Difference between Convex and Concave lens

## Difference between Convex and Concave lens

A lens is a transparent material bound by two surfaces, in which one or both of the surfaces are bulged outward or bent inward. In a lens at least one surface is spherical and another surface would be plane. Lenses are of two kinds, concave and convex. Do you have an idea what is the difference between a convex lens and a concave lens? Here you are going to get a complete idea of the difference between concave and convex lenses.

The kind of lens in which at least one surface bulges outward is simply called a convex lens and the kind of lens in which at least one surface is bent inward is simply called a concave lens. A lens may have both spherical surfaces,if both of the surfaces of the lens are bulged outward then it is called a double convex lens, and the lens in which both of the surfaces are bent inward is known as a concave lens.

The lenses are carved out from a sphere, both of the surfaces form a part of a sphere. The centres of these spheres are known as centres of the curvature of the lens, both of the centres of the curvature are represented by C1 and C2.

The imaginary straight line passing through the centres of curvature of the lens is known as the principal axis.

The diameter of the circular outline of a spherical lens is called its aperture and its centre is known as the optical centre,it is usually represented by the letter O.

In this page, we are going to discuss the thin lenses, which are usually used in the spectacles, the lenses used in specs have much less aperture than the radius of the curvature of the lens.

Practically you would have experience of handling such types of lenses, when a beam of light is allowed to pass through a lens and you tried to focus these light rays at a point on a plane of the paper and the paper started to burn, actually it happens because of the formation of sun’s real image on the paper. In this phenomenon, the lens converged all the light rays to a point that is the focal point of the lens.All the light rays meet at at a point that increases the inensity of heat which reaches to the burning temperature and the paper starts to burn.

## Difference between Convex and Concave lens

Convex lens         Concave lens
A convex lens is thicker in the middle and thinner at the edges.

A concave lens is thinner in the middle and thicker at the edges.

After the refraction of the incoming rays, a convex lens concentrates them at a single point, therefore it is also called a converging lens.

After the refraction of the incoming rays, a concave lens extends them in a different direction, therefore it is also called a diverging lens.

The focal length of the convex lens is negative.

The focal length of the concave lens is positive.

The image formed by the convex lens is generally a real erected image that is of a larger size than the object.

The image formed by the concave lens is always a virtual image that is of a smaller size than the object.

The position of the image depends on the position of the object in the case when the object is at a finite distance.The position of the image is always formed between the optical centre and the focal point regardless of the position of the object in the case when the object is at a finite distance.

### Application of  Concave and Convex Lenses:

• Concave lenses are used to correct myopia(i.e nearsightedness) because it diverges the light rays therefore able to shift the image of the object from the near of the lens to the retina.
• A concave lens is used in medical equipment, CD, and DVDs for scanning a specific area, as it disperses a beam of light(i.e leisure beam).
• A combination of convex and concave lenses is widely used by camera manufacturers for improving the quality of photographs.
• A concave lens is used in the flashlight to magnify the light produced by the source.
• A concave lens is used in peepholes or door viewers as a security device used to see a wider view of the object.
• Convex is used to correct hypermetropia(farsightedness), used in cameras, and used in magnifying glasses. used in a simple telescope.

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