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Difference Between Concave and Convex Lenses

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A transparent substance joined by two spherical surfaces—either one or both—creates a lens. These are typically transparent glasses or plastic that are circular, have two main sides, and are molded or polished in a way that produces either a convergence or divergence of light. Basic laws of physics like reflection and refraction govern the functioning of the lens. Based on the nature of their interaction with light, lenses can be classified primarily into two types, Concave and Convex lens.

The main difference between a concave lens and a convex lens is that a concave lens diverges the light passing through it, whereas a convex lens converges the beam of light passing through it. 

This article will further discuss the differences in more detail. We will talk about how they interact with light and other differences between them. Let’s get started!

What is a Concave Lens?

Vector illustration of a Concave Lens

A concave lens bends a straight light beam away from the source and focuses it into a shortened, upright, and virtual projection. Both actual and virtual images can be created using it. In a concave lens, at least one internal surface is curved.

Since it is rounded in the center and bulges outward at the borders, a concave lens diverges light through it. It is also known as a diverging lens. They make distant things appear smaller than they actually are, and thus they are used to cure myopia.

What is a Convex Lens? 

Vector illustration of a Convex Lens

The lens is referred to as a biconvex lens or just a convex lens if the surfaces of the lens are curved outwards. They are thicker in the middle and thinner on the edges.

These lenses can focus an outside light beam onto a spot on the opposite side by converging it. Thus, they are also known as converging lenses. Besides biconvex lenses, there is a plano-convex lens, in which one of the surfaces is flat and the other convex.

Key Differences between Concave Lenses and Convex Lenses

Nature of the image

Concave lens: The image formed of an object by a concave mirror gets diminished in size. It is also virtual and upright in position. The location of the image formed does not depend upon the object's position. It is always formed between the object and the lens.

When an item is positioned at infinity, the focus of the concave lens creates a virtual picture of the thing. The image's size is greatly reduced to a point size. On the other hand, a virtual picture is created between the convex lens' optical center and focus when an item is positioned at a specific distance from the lens. The picture is smaller than the object in terms of size.

Convex lens: In a convex lens, the image of the object formed is real, inverted, and diminished when it is kept in focus. When an item is positioned at twice the distance of the focal point, a picture that is real, inverted, and the same size as the object results. Whereas when an item is positioned between 2F and F, an actual, inverted picture that is bigger than the object is created.

Appearance

As evident from the name, the concave name looks like a cave, and the spherical surface curves inside. They are thinner in the center and thicker at the edges. Contradictorily, the spherical surfaces of a convex lens bulge outwards, making them thicker in the middle and thinner at the edges.

Focal length

The distance between the center of the lens and its focus is called its focal length. The focal length of a concave lens is negative, and the focal length of a convex lens is positive.

Nature of interaction with light

A concave lens moves or diverges the incident light beam away from its principal axis. Meanwhile, a convex lens moves or converges an incident beam of light towards its principal axis. 

Comparison Chart: Concave Vs Convex Lenses

ParametersConcaveConvex
Nature of the image formedAlways virtualIt can be real or virtual.
Image positionUprightIt can be upright or inverted.
Converging or divergingDivergingConverging
ApplicationsIt is used in glasses, certain telescopes, door spy holes, etc.It is used in overhead projectors, projector microscopes, basic telescopes, magnifying glasses, and cameras to concentrate sunlight. 
Nature of focal lengthNegativePositive

Similarities between Concave and Convex Lenses

Convex and concave lenses have some fundamental similarities, but closer examination reveals more differences than similarities.

The main similarity is that they both operate on the same fundamental idea, whereby the lens's ability to bend light rays and produce a focal point is realized by the difference in refractive indices between the lens and the medium around it. 

Concave and convex lenses become more identical to one another when the lens's curvature lowers, and the shape of the surface gets more similar.  

FAQs

Which lens is used to cure the short-sightedness of the eye?

Concave lenses are used to cure the short-sightedness of the eye, while convex lenses are used to cure the long-sightedness of the eye.

Can a concave lens form a real image?

No, the image formed by a concave lens is always virtual.

What is the power of a lens?

The power of a lens is defined as the ability to cause the light rays that strike it to converge or diverge. 

What happens when a concave and a convex lens are combined?

If a concave and a convex lens of the same focal length are combined, the power becomes zero.

Conclusion

So, what is the difference between a concave and a convex lens? In short, a concave lens bends light outward while a convex lens bends it inward. This change in direction causes images to appear differently depending on which type of lens is being used. Hopefully, this post has helped clear up any confusion about these two types of lenses and their various uses.

References

Feel free to comment and discuss about the article in the comment space below if you have any information or remarks to add. If you think we made a mistake, you can also report it there.

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About the Author: Nicolas Seignette

Nicolas Seignette, who holds a scientific baccalaureate, began his studies in mathematics and computer science applied to human and social sciences (MIASHS). He then continued his university studies with a DEUST WMI (Webmaster and Internet professions) at the University of Limoges before finishing his course with a professional license specialized in the IT professions. On 10Differences, he is in charge of the research and the writing of the articles concerning technology, sciences and mathematics.
All Posts Written By Nicolas Seignette

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