For a Concave mirror, object can be kept at different positions

Hence, we take different cases


Case 1 - Object is Placed at infinity

Concave Mirror - Object at Infinity - Ray Diagaram - Teachoo.jpg

In this Case, Object AB is kept far away from mirror (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 reflection

 

Hence, Image is formed at Focus

And it is very very small

 

We can say that

  • Image is in Front of the Mirror (Real Image)
  • Image is Inverted
  • Image is Smaller than the Object (Highly Diminished)

 

Case 2 - Object is beyond Center of Curvature (C)

Concave Mirror - Object beyond Center of Curvature - Teachoo.jpg

 

Here, Object AB is beyond C

 

First, we draw a ray parallel to principal axis

So, it passes through focus after reflection

 

We draw another ray which passes through Center of Curvature

So, the ray will go back along the same path after reflection

 

Where both reflected rays meet is point A'

And the image formed is A'B'

This image is formed between Center(C) and Focus (F)

 

We can say that

  • Image is in Front of the Mirror (Real Image)
  • Image is Inverted
  • Image is Smaller than the Object (Diminished)

Case 3 - Object is at Center of Curvature (C)

Concave Mirror - Object at Center of Curvature - Teachoo.jpg

 

Here, Object AB is kept at C

 

First, we draw a ray parallel to principal axis

So, it passes through focus after reflection

 

We draw another ray which passes through Focus

So, the ray will reflect back parallel to the principal axis

 

Where both reflected rays meet is point A'

And the image formed is A'B'

This image is formed between at Center(C)

 

We can say that

  • Image is in Front of the Mirror (Real Image)
  • Image is Inverted
  • Image is exactly the same size as that of Object

Case 4 - Object is between Center of Curvature (C) and Focus (F)

Concave Mirror - Object between C & F - Teachoo.jpg

Here, Object AB is kept between C and F

 

First, we draw a ray parallel to principal axis

So, it passes through focus after reflection

 

We draw another ray which passes through Center of Curvature

So, the ray will go back along the same path after reflection


Where both reflected rays meet is point A'

And the image formed is A'B'

This image is formed between beyond Center(C)

 

We can say that

  • Image is in Front of the Mirror (Real Image)
  • Image is Inverted
  • Image is larger than the object (Magnified)

Case 5 - Object is at Focus (F)

Concave Mirror - Object at Focus - Teachoo.jpg

 

Here, Object AB is kept at F

 

First, we draw a ray parallel to principal axis

So, it passes through focus after reflection

 

We draw another ray which passes through Center of Curvature

So, the ray will go back along the same path after reflection

 

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 in Front of the Mirror (Real Image)
  • Image is Inverted
  • Image is larger than the object (Magnified)

Case 6 - Object is between Pole (P) and Focus (F)

Concave Mirror Object between Pole (P) & Focus (F) -Teachoo.jpg

Here, Object AB is kept between P and F

 

First, we draw a ray parallel to principal axis

So, it passes through focus after reflection

 

We draw another ray which passes through Center of Curvature

So, the ray will go back along the same path after reflection


We observe that both reflected rays are diverging

It means that they would have met at some point

Hence, we extend both reflected rays behind the mirror

 

We see that the rays form an image behind the mirror.

So, the image is virtual

And image formed would be larger than the object

 

We can say that

  • Image is behind the Mirror (Virtual Image)
  • Image is erect
  • Image is larger than the object (Magnified)

Note: - 
Real image is formed in front of mirror

Virtual Image is formed behind the mirror

 

And,

Inverted image is upside down

Erect image is straight

To summarize

Position of the
object
Position of the
image
Size of the
image
Nature of the
image
At infinity At the focus F   Highly diminished,
point-sized
Real and inverted
Beyond C  Between F and C  Diminished  Real and inverted
At C  At C  Same size  Real and inverted
Between C and F  Beyond C  Enlarged  Real and inverted
At F  At infinity  Highly enlarged  Real and inverted
Between P and F  Behind the mirror  Enlarged  Virtual and erect

 

Questions 

Question 3 Page 168 - Name a mirror that can give an erect and enlarged image of an object

View Answer

 

NCERT Question 2 - The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?

(a) Between the principal focus and the centre of curvature

(b) At the centre of curvature

(c) Beyond the centre of curvature

(d) Between the pole of the mirror and its principal focus.

View Answer

 

  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.