# Difference between Concave and Convex Lens

Physics comprises of many vivid terms and topics like gravity, inertia, kaleidoscopic images, concave mirror, convex mirror, etc. But there is one topic that we have always been confused about, i.e., concave and convex lens. In physics, there are several contrasting points between them. Therefore, it is essential to know the basic meaning of these two terms, followed by a table of differences. So, let us begin.

## Concave Lens

In physics, a concave lens is defined as a lens that has a curved surface. The surface is curved inwards. A concave lens is basically a diverging lens that spreads the beam of light in different directions. A concave lens is a thin lens that is used by people having short-sightedness. There are two significant kinds of concave lenses, namely biconcave lens and plano-concave lens. Concave lenses are used in spectacles, cameras, lasers, flashlights, etc. The concave lens forms a smaller image of an object. That is why the concave lens is called a diverging lens because it creates virtual images of the objects.

## Convex lens

The convex lens is defined as an optical lens that consists of two curved/ spherical surfaces. If the lens is turned in an outward direction, it is called a biconvex lens. The rays are converged and fall in a parallel direction through the convex lens. The surface is covered outwards instead of being curved inwards. Convex lenses are used in eyeglasses, magnifying glasses, microscopes, cameras (to capture the image from a distance), etc. The formula for the convex lens is 1/f = 1/v + 1/u. In this formula, 'f' is the focal length, 'v' is the distance from where the image is formed, and 'u' is the distance between the lens and the object. There are three significant kinds of convex lenses, namely plano-convex lens, a double convex lens, concave-convex lens.

Fig: Difference between Convex and Concave lens

Now, there are certain differences between the convex and concave lens. So, let us discuss them.

S.NO. CONCAVE LENS CONVEX LENS
1. A concave lens is defined as a lens that spreads the light beam in different directions. On the other hand, a convex lens is defined as a lens wherein the rays reflected through the surface are spread in a parallel direction.
2. A concave lens is called as a diverging lens. A convex lens is called as a converging lens.
3. A concave lens has one curved surface. The surface is curved inwards. On the other hand, a convex lens has two spherical surfaces, one of which is curved outwards.
4. It has a real focus. It has a virtual focus.
5. A concave mirror's magnification is greater, equal to, or less than one. A convex mirror's magnification is less than one.
6. A concave lens has thick edges and is thin in the middle. A convex lens has thin edges and is thick in the middle.
7. A concave lens is used for people suffering from myopia. A convex lens is used for people suffering from hypermetropia.
8. The focal length of a concave mirror is negative. The focus length of a convex mirror is positive.
9. The image formed in a concave lens is virtual, upright, and small in size. The image formed in a convex lens can be small or large in size. The image formed is real and inverted.
10. A concave lens is used in objects like flashlights, cameras, and lasers. A convex lens is used in objects like magnifying glasses, microscopes, etc.

So, these are the significant points of difference between the convex and concave lens. It is essential to note that both concave and convex lenses are used in various objects for various purposes. So, let us discuss in detail the types of concave and convex lenses.

## Types of Concave Lens

1. Biconcave Lens: The surface having a concave lens on both sides is termed as a biconcave lens. Biconcave lenses are the diverging lens, i.e., the light beam is reflected in different directions.
2. Plano-Concave Lens: A plano-concave lens is defined as the lens wherein one surface is plane and the other is concave. These lenses are used for the projection of light, beam expansion, etc.
3. Negative Meniscus: Negative Meniscus is a diverging lens in which one edge is convex, and the other edge is concave.

## Types of Convex Lens

1. Biconvex Lens: A biconvex lens is a lens in which both surfaces are convex. Biconvex lenses are the converging lens.
2. Plano-Convex Lens: A plano-convex lens is a lens wherein one surface is plane, and the other surface is convex. Plano-convex lenses are used to focus and collect light beams and converge them in a parallel direction.

So, these are the types of concave and convex lenses. Now, let us look at some of the uses of these lenses.

## Uses of Concave Lens

1. Glasses: A concave lens is majorly used by people suffering from myopia or short-sightedness. The image formed in the retina is relatively small because the light beams spread out.
2. Lasers: A concave lens is used in many medical machines, scanners, CD players, etc., that emit laser beams. The beams are spread in different directions, due to which they work correctly.
3. Camera: Concave lenses are used in cameras to get good quality pictures. Basically, both convex and concave lenses are used in cameras to get a clear image of objects.
4. Flashlights: A concave lens is used in flashlights to expand or magnify the light.

## Uses of Convex Lens

1. Glasses: A convex lens is used to treat hypermetropia or long-sightedness. When the eye-lens is unable to focus the light, the image is formed behind the retina. That is why convex lenses are used in spectacles.
2. Microscopes: Convex lenses are used in microscopes to generated magnified images of small objects.

So, these are the uses of concave and convex lenses. The most fundamental difference between them is of the reflection of light, i.e., the concave lens spreads the light beam in different directions, while a convex lens spreads the light in a parallel direction. Thus, both convex and concave lenses have their own uses and differences.

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