For a Concave lens,

There are only 2 cases

 

They are

  • Object is Placed at Infinity
  • Object is Placed between Infinity and Optical Center

 

Case 1 - Object is Placed at infinity

Concave Lens Object at infinity - Ray Diagram - Teachoo.jpg

 

In this Case, Object is kept far away from mirror (almost at infinite distance)

So, we draw rays parallel to principal axis

Since ray parallel to principal axis appear to pass through the Focus

All rays appear to meet at focus after refraction

 

Hence, Image is formed at Focus

And it is on the left side of the lens. So, Image is virtual

And it is very very small

 

We can say that

  • Image is virtual (left side of the lens)
  • Image is Erect
  • Image is Smaller than the Object (Highly Diminished)

 

Case 2 - Object is between Infinity and Optical Center

Concave Lens - Object between infinity and Optical Center - Teachoo.jpg

Here, Object AB kept anywhere on the principal axis - between Infinity and Optical Center (O)

 

First, we draw a ray parallel to principal axis

So, it appears to pass through focus after reflection

 

We draw another ray which passes through Optical Center

So, the ray will go through without any deviation


Where both reflected rays meet is point A'

And the image formed is A'B'

This image is formed between F 1 and Optical Center (O)

 

We can say that

  • Image is behind the Mirror (Real Image)
  • Image is Erect
  • Image is Smaller than the Object (Diminished)

 

To summarise

Position of the object Position of the image Relative size of the image  Nature of the image
At infinity  At focus F 1 Highly diminished, Point - Sized  Virtual and erect
Between infinity and optical centre O of the lens  Between focus F 1 and optical centre O  Diminished Virtual and erect
  1. Class 10
  2. Chapter 10 Class 10 - Light - Reflection and Refraction

About the Author

Davneet Singh's photo - Teacher, Computer Engineer, Marketer
Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.