For a Convex Lens, object can be kept at different positions

Hence, we take different cases

 

Case 1 - Object is Placed at infinity

Convex Lens Object at Infinity - Ray Diagram - Teachoo.jpg

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

So, we draw rays parallel to principal axis

Since ray parallel to principal axis passes through the Focus

Both rays meet at focus after refraction

 

Hence, Image is formed at F 2

And it is very very small

 

We can say that

  • Image is Real
  • Image is Inverted
  • Image is Smaller than the Object (Highly Diminished)


Case 2 - Object is beyond 2F

Convex Lens - Object beyond 2F - Teachoo.jpg

 

Here, Object AB is beyond 2F 1

 

First, we draw a ray parallel to principal axis

So, it passes through focus after refraction

 

We draw another ray which passes through Optical Center

So, the ray will go through without any deviation


Where both rays meet is point A'

And the image formed is A'B'

This image is formed between F 2 and 2F 2

 

We can say that

  • Image is Real
  • Image is Inverted
  • Image is Smaller than the Object (Diminished)

 


Case 3 - Object is at 2F

Convex Lens Object at 2F - Teachoo.jpg

 

Here, Object AB is at 2F 1

 

First, we draw a ray parallel to principal axis

So, it passes through focus after refraction

 

We draw another ray which passes through Optical Center

So, the ray will go through without any deviation

 

Where both refracted rays meet is point A'

And the image formed is A'B'

This image is formed at 2F 2

 

We can say that

  • Image is Real
  • Image is Inverted
  • Image is exactly the same size as that of Object

Case 4 - Object is between F and 2F

Convex Lens - Object beyond F and 2F - Teachoo.jpg

 

Here, Object AB is kept between F 1 and 2F 1

First, we draw a ray parallel to principal axis

So, it passes through focus after refraction

We draw another ray which passes through Optical Center

So, the ray will go through without any deviation

 

Where both refracted rays meet is point A'

And the image formed is A'B'

This image is formed between beyond 2F 2

 

We can say that

  • Image is Real
  • Image is Inverted
  • Image is larger than the object (Magnified)

 

Case 5 - Object is at F

Convex Lens - Object at F - Teachoo.jpg

Here, Object AB is kept at F 1

 

First, we draw a ray parallel to principal axis

So, it passes through focus after refraction

 

We draw another ray which passes through Optical Center

So, the ray will go through without any deviation


We observe that both rays are parallel to each other

Hence we can say that they meet at infinity.

Hence, the rays form an image at infinity

And image formed would be larger than the object

 

We can say that

  • Image is Real
  • Image is Inverted
  • Image is larger than the object (Magnified)

Case 6 - Object is between O and F

Convex Lens - Object between Optical Center and Focus (O and F) - Teachoo.png

Here, Object AB is kept between O and F 1

 

First, we draw a ray parallel to principal axis

So, it passes through focus after refraction

 

We draw another ray which passes through Optical Center

So, the ray will go through without any deviation

 

We observe that both refracted rays are diverging

It means that they would have met at some point

Hence, we extend both rays behind the lens

 

We see that the rays form an image behind the lens (on the left side).

So, the image is virtual

And image formed would be larger than the object

 

We can say that

  • Image is virtual (behind the lens)
  • Image is erect
  • Image is larger than the object (Magnified)

To summarise

Position of the object Position of the image Relative size of the image  Nature of the image
At infinity  At focus F 2   Highly diminished,  point-sized Real and inverted
Beyond 2F 1   Between F 2 and 2F Diminished  Real and inverted
At 2F 1   At 2F 2   Same Size Real and inverted
Between F 1 and 2F Beyond 2F 2   Enlarged  Real and inverted
At focus F At infinity Infinitely large or
highly enlarged
Real and inverted
Between focus F 1 and optical Center O On the same side of the lens as the object Enlarged  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.