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Syllabus

Concave Lens

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Topics

  • Introduction
  • Applications

Introduction

A concave lens is a type of lens that diverges light rays, spreading them outward. It is made by joining two spherical surfaces, where the lens is thin at the centre and thick at the edges. Due to its diverging property, it is also called a diverging lens.

When parallel rays of light pass through a concave lens, they spread out (diverge) away from a common point. This results in the formation of a virtual, upright, and diminished image. Because of this property, concave lenses are widely used in correcting myopia (nearsightedness) by making distant objects appear smaller and clearer.

A concave lens may be of the following three kinds:

  1. Bi-concave or double-concave or equi-concave,
  2. Piano-concave, and
  3. Convexo-concave. 

Applications:

1. Optical Instruments

  • Telescope & Binoculars: Used to correct distortions and improve focus.
  • Microscopes & Cameras: Enhances image quality by reducing aberrations.

2. Vision Correction

  • Eyeglasses for Myopia: Helps nearsighted people see distant objects clearly by diverging light rays before they reach the retina.

3. Security Devices

  • Peepholes in Doors: Provides a wide-angle view by minimising object proportions.

4. Light and Laser-Based Devices

  • Medical Equipment & Scanners: Used in laser-based devices for precise functioning.
  • CD Players: Helps in focusing laser beams for reading discs.
  • Torchlights: Spread light widely from a small bulb.
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Related QuestionsVIEW ALL [121]

Define the principal focus of a concave lens.  

Distinguish between:

Concave Lens and Convex Lens

What kind of lens is used to correct 

short-sightedness 

Where will the image be formed if an object is kept in front of a concave lens at a distance equal to its focal length? Draw a ray diagram to illustrate your answer.

A person finds difficulty in seeing nearby objects clearly. His vision can be corrected by using spectacles containing:
(a) converging lenses
(b) diverging lenses
(c) prismatic lenses
(d) chromatic lenses

If the numerical value of the power of this lens is 10 D, what is its focal length in the Cartesian system ? 

 An object 2 cm tall stands on the principal axis of a converging lens of focal length 8 cm. Find the position, nature and size of the image formed if the object is:
(i) 12 cm from the lens
(ii) 6 cm from the lens
 State one practical application each of the use of such a lens with the object in position (i) and (ii). 

Define the term principal foci as applied to a concave lens. Illustrate your answer with the aid of proper diagrams. Show the focal length of the lens in the diagram.

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