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Difference Between Convex and Concave Lens

Knowing the difference between convex and concave lens is one of the confusing topics for students in the field of optics. In this article, we will learn all the major and minor differences between the convex lens and concave lens.

Lenses are devices that transmit light and modify its path due to refraction. They are transparent and can be used to converge or diverge light. 

Simple lenses consist of only one type of medium and are curved. Based on curvature, they are classified as a convex lens or a concave lens.

Related Topic: Biconvex Lens

Difference Between Concave Lens and Convex Lens

Here, we have listed out the difference between concave lens and convex lens in a single table.

CategoryConcave lensConvex lens
AppearanceThey are thicker at the edges and thinner in the middle.Convex lenses are thicker at the middle and thinner at the edges.
Interaction with Incident Light RaysThey make incident light rays diverge.They make incident light rays converge.
Focal LengthFocal length is positiveFocal length is negative
UsageConcave lenses are used in glasses with people with short sight (myopia).
They are also used in spyglasses and some kinds of telescopes.
Convex lenses are used in microscopes and magnifying lenses.
They are also used in projectors and cameras.
They are used for glasses for people with long sight (hypermetropia).
Image Formation– For a real object, the image is always virtual and erect.
– It is formed between the lens and object.
– Images formed are diminished.
For a real object, there are various image types based on position. Let focal distance be f.
– If the object is between focus and pole of lens, image is magnified, erect and virtual. It is on same side as object.
– If the object is at focus, image is real and is formed at infinity.
– If the object is between f and 2f, image is real, inverted and magnified. It is located beyond 2f on the other side.
– If the object is at 2f, image is real, inverted and same size. It is located at 2f on the other side.
– If the object is beyond 2f, image is real, diminished and inverted. It is between f and 2f on the other side.
– If the object is at infinity, image is real, highly diminished and formed at f. It is inverted.

Image Formation Diagrams

Now, let’s look into various images formed by these two lenses on various conditions, which will further help us to find the difference between convex lens and concave lens.

Convex Lens

Formation of Image by Convex Lens for Different Positions of Objects - Difference Between Convex and Concave Lens
Formation of Image by Convex Lens for Different Positions of Objects (Source)

Concave Lens

Formation of Image by Concave Lens for Different Positions of Objects - Difference Between Convex and Concave Lens
Formation of Image by Concave Lens for Different Positions of Objects (Source)

FAQs

What are the uses of convex and concave lenses in vision correction?

Convex lenses are used to correct farsightedness (hypermetropia).
Concave lenses are used to correct nearsightedness (myopia).

What are the different types of convex lens?

The different types of convex lens are:
1. Plano-convex lens: It has one plane side and one convex side. 
2. Biconvex (or just convex) lens: It is convex on both sides.
3. Concavo-convex lens: It is concave on one side and convex on other side.

What are the different types of concave lens?

The different types of convex lens are:
1. Plano-concave lens: It has one plane side and one concave side. 
2. Biconcave (or just concave) lens: It is concave on both sides.
3. Convexo-concave lens: It is convex on one side and concave on other side.

How can you tell apart a concave and convex lens without feeling its surface?

We can tell apart a convex and concave lens without touching its surface as follows.
We pass a stream of light from a distant source (like the Sun) onto the lens. Then we put a paper in front of the lens and adjust its position.
– If a small point image is formed, the lens is convex.
– If no image is formed despite adjusting position, the lens is concave

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