Making the Concept of Convex Lenses Easier to Grasp

Lenses are always fascinating. They are used for anything and everything, from focusing on small objects to rays of the sun. Of all the lenses, convex lenses are very interesting. They are made of either transparent glass or plastic.

Convex lenses are the most common lenses because of their multiple uses. Let us go through the uses, types, magnification, and function of convex lenses. Let us see the uses, types and Convex Lens Function.

Convex lens:  Any optical lens that is thin in the sides (upper and lower edges) and thick in the middle is called a convex lens. A convex lens is also known as a converging lens or positive lens. When light passes through a convex lens, it converges, i.e. the light rays are brought closer to a point, which is known as the principal focus. Convex lenses are grouped into three types. They are bi-convex, plano-convex and concave-convex lenses.

Bi-convex lenses: These are lenses, which have two spherical surfaces. They have a shorter focal length compared to plano-convex lenses. These are used in projectors, telescopes, cameras, etc.

Plano-convex lenses: These are lenses with positive focal lengths.  They have one spherical surface and one flat surface. These lenses are used for all-purpose focusing lenses.

Concave-convex lenses: These lenses are a combination of concave and convex lenses. These lens curve inwards from one side and outwards from the other side. These lenses are usually used to correct the spherical irregularities that the other lenses have caused. Convex lenses are used in a wide number of instances. A few convex lens uses are explained below.

1. The most common use of convex lenses is to help us see better. It is used for the correction of hyperopia or hypermetropia. When the eye lens fails to focus the light on the retina, the person suffers from either farsightedness or nearsightedness.

In a person suffering from hyperopia, the eye lens focuses the image far behind the retina. Therefore, the person cannot see objects close to the eye. A convex lens bends the light rays and helps the light focus on the retina properly.

2. Convex lenses are used in microscopes and magnifying glasses. All the light passing through the lens converges to a specific point in front of the middle of the lens. The focal point will reach the object, thus magnifying the object to the maximum.
3. Convex lenses are used in cameras to focus light rays for clear and magnified images.
4. Convex lenses are used in the projector.
5. Convex lenses are the primary concentrator for multi-junction solar cells.
6. Plano-convex lenses are used in telescopes.
7. Convex lenses are also used to correct the spherical irregularities that the other lenses have caused. It is also used to control the laser beam.

Magnification of convex lens

Magnification is defined as an increase in the size of the image created by the lens compared to the actual size. It is the ratio between the height of the image and the height of the object. It is represented by the symbol ‘m.’

If h denotes the object height and h’ denotes image height formed by the lens, then magnification m is given by the below formula.

magnification(m)= height of the object/height of the lens = h’/h

Magnification formed by the lens is also related to object distance ‘u’ and image distance ‘v’. The magnification for this is found by

magnification (m) = h’/h = v/u

A magnification of 2 represents that the image is twice the size corresponding to the object. A magnification of 1 represents the image is equal to the object in size.

The height of the image is taken as positive for real images. Similarly, it is to be taken as negative for virtual images. If the magnification value is negative, then the image is considered real. If the magnification value is positive, then the image is considered virtual.

Functions of a convex lens

Now, let us focus on some functions of a convex lens.

1. When the object’s position is at the point of infinity, the image is formed at the focus. The size of the image formed is highly diminished, and the image is real.
2. When the object’s position is behind the imaginary point, the image is formed in the middle of the focal point and an imaginary point. The size of the image formed is real, diminished, and inverted.
3. When the object’s position is near the imaginary point, the image is formed toward the imaginary point. The size of the image formed is actual, inverted, and the size is identical.
4. When the object’s position is in the middle of the focal point and imaginary point, the image is formed behind the focal point and an imaginary point. The size of the image formed is actual, inverted, and enlarged.
5. When the object’s position is towards the focal point, the image is formed at the point of infinity. The size of the image formed is actual, inverted, and enlarged.
6. When the object’s position is in the middle of the focal point and the axis of curvature, then the image is formed behind the imaginary point and the object. The size of the image formed is virtual and enlarged.

Real image and virtual image

Real image: A convex lens can produce a real image if the object is positioned at more than one focal length from the lens. The image is projected before the lens and captured on screen. These are used in movie theatres and projectors.

Virtual image: These lenses can produce a virtual image if the object is placed in front of the focal point. Convex lenses are used in spectacles to produce clear images.

Conclusion

The above article is a brief description of convex lens uses, types, definitions, and functions. Convex lenses have a wide range of uses in our daily lives. For example, it helps us from seeing better to creating a magnified image. It is used in magnifying lenses such as telescopes, projectors, etc.