Lenses in Physics: Definition, Types, Properties & Applications

What is a Lens?

A lens is a transparent piece of glass or plastic that bends light when it passes through it. This bending of light is called refraction. Lenses are designed in such a way that they can either bring light rays together or spread them apart.

In physics, lenses are mainly classified into two types based on their shape and behavior with light:

1. Convex Lens

2. Concave Lens

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Types of Lenses in Physics

1. Convex Lens

A convex lens is thicker at the center and thinner at the edges. It is also known as a converging lens because it brings parallel light rays together at a single point called the focus.

Properties of Convex Lens

• Thicker at the center, thinner at the edges

• Converges light rays

• Can form real and virtual images

• Image can be inverted or erect depending on object position

• Has a positive focal length

Image Formation by Convex Lens

• When the object is far away, the image is real and inverted

• When the object is placed very close to the lens, the image is virtual and magnified

Applications of Convex Lens

• Used in magnifying glasses

• Used in microscopes to see small objects

• Used in telescopes to view distant objects

• Used in cameras

• Used in spectacles to correct long-sightedness (hypermetropia)

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2. Concave Lens

A concave lens is thinner at the center and thicker at the edges. It is also called a diverging lens because it spreads light rays away from each other.

Properties of Concave Lens

• Thinner at the center, thicker at the edges

• Diverges light rays

• Always forms a virtual, erect, and smaller image

• Has a negative focal length

• Image cannot be obtained on a screen

Image Formation by Concave Lens

• The image is always formed on the same side of the lens

• The image is smaller and upright

Applications of Concave Lens

• Used in spectacles to correct short-sightedness (myopia)

• Used in door viewers or peepholes

• Used in cameras along with convex lenses

• Used in binoculars and optical instruments

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Difference Between Convex and Concave Lens

Important Terms Related to Lenses

Optical Centre

The optical centre is the point in the lens through which light passes without bending.

Principal Axis

The principal axis is an imaginary straight line passing through the optical centre.

Focus

The focus is the point where light rays meet (convex lens) or appear to meet (concave lens).

Focal Length

The focal length is the distance between the optical centre and the focus of the lens.

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Uses of Lenses in Daily Life

Lenses play an important role in our everyday life. Some common uses include:

• Spectacles to correct vision problems

• Cameras to capture clear photos

• Microscopes to study tiny organisms

• Telescopes to observe stars and planets

• Projectors to display images

Without lenses, many modern devices would not work properly.

Why Are Lenses Important for Students?

Studying lenses helps students understand:

• How light behaves

• How images are formed

• How optical instruments work

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