Images Formed by a Concave

Mirror

VII std Science

(State Syllabus)

B. Dhandapani

Teacher Educator

Block Resource Centre Sarva Shiksha Abhiyan

Mannargudi BlockThiruvarur District

Tamil Nadu

Email bdpani@rediffmail.com

Project Done by:

To understand the basic principles of Ray optics

To understand the principles of “Construction” of ray diagrams

To explain how the images are formed by the concave mirrors for various positions of objects

Basic Principles

Terms Used in Concave Mirrors

Construction - Title

Construction 1

Construction 2

Construction 3

Images Formed - Title

Object at Infinity

Object beyond ‘C’

Object at ‘C’

Object between ‘F’ and ‘C’

Object at ‘F’

Object between ‘P’ and ‘F’

All in One

Relative Movement of the Object and the Image

Ready Reckonor

Uses of Concave Mirrors

Test Your Understanding

Click on the headings to study the relevant topic

Spherical Mirrors are Portions of spherical surfaces

If the outside of the spherical mirror is silvered, then it is called a concave mirror

Concave Mirror

Index

Pole (P) (C) Centre of Curvature

The Line Passing through C,P – Principal Axis

Terms Used in Spherical Mirrors

P – Pole

C – Centre of Curvature

Principal Axis

Geometrical Centre

Centre of the sphere of which the mirror is a part

Index

Index

Principal Axis

Construction 1

F

Ray Parallel to Principal Axis

Rule 1. The Ray Parallel to Principal Axis is reflected through the Principal Focus ‘F’

Index

F Principal Axis

Construction 2

Ray Passing through ‘F’

Rule 2. Ray Passing through the principal focus ‘F’ is reflected parallel to the Principal Axis .

Index

F Principal AxisC

Construction 3

Rule 3. The ray passing through the Centre of Curvature ‘C’ is reflected through the same path.

Index

Index

F C

All the Rays of the Object at infinity are parallel to Principal Axis and hence according to Construction 1 the image is formed at ‘F’.

Index

F C

There are two rays emerging from the object which is placed beyond ‘C’. One ray is parallel to Principal Axis and the other ray passes through ‘C’. Both the rays meet at the point between ‘F’ and ‘C’ where the image is formed.

1

2

Index

F C

There are two rays emerging from the object which is placed at ‘C’. One ray is parallel to Principal Axis and the other ray passes through ‘F’. Both the rays meet at the point ‘C’ where the image is formed

1

2

Index

F C

There are two rays emerging from the object which is placed between ‘F’ and ‘C’. One ray is parallel to Principal Axis and the other ray passes through ‘C’. Both the rays meet at the point beyond ‘C’ where the image is formed.

21

Index

F C

There are two rays emerging from the object which is placed at ‘F’. One ray is parallel to Principal Axis and the other ray passes through ‘C’. Both the rays meet at the point of infinity.

2

1

Index

F C

There are two rays emerging from the object which is placed between ‘P’ and ‘F’. One ray is parallel to Principal Axis and the other ray passes through ‘C’. Both the rays meet at the back of the mirror when the rays are extended. The virtual image is formed at the back of the mirror.

P

1

2

Index

P

CF

Object @ Infinity – Image @ ‘F’ – Real, Inverted

Object beyond ‘C’ – Image between ‘F’ & ‘C’- Real, Inverted

Object @ ‘C’ – Image @ ‘C’ – Real, Inverted.

Object between ‘F’ & ‘C’ – Image beyond ‘C’ – Real, Inverted

Object

Image

Infinity

…All in One (Recap)

Index

Object

Image

When the Object moves closer to the Mirror,

The Image Moves away from the Mirror

Index

SlNo Place of the Object

Place of the Image Formed

Rays to be Drawn Nature of the Image

1 At Infinity At ‘F’All Rays Parallel to Principal Axis (PA)

Real, Inverted, Small

2 Beyond ‘C’ Between ‘F’ & ‘C’

Ray 1 Parallel to PA & Ray 2 Through ‘C’

Real, Inverted, Small

3 At ‘C’ At ‘C’Ray 1 Parallel to PA & Ray 2 Through ‘F’

Real, Inverted, Same as Object

4 Between ‘F’ & ‘C’

Beyond ‘C’Ray 1 Parallel to PA & Ray 2 Through ‘C’ Real,

Inverted, Large

5 At ‘F’ At InfinityRay 1 Parallel to PA & Ray 2 Through ‘C’ --

6 Between ‘F’ & ‘C’

At the Back of the Mirror

Ray 1 Parallel to PA & Ray 2 Through ‘C’

Virtual, Large, Straight

Index

•Used in search light, car lights and telegraphic intermittent lights.

Used in mirror telescopes (its front is a silver-plated mirror)

•The spherical concave mirror finds its most valuable application as eye mirror (Helmholtz 1851). It serves during examination of the inside of eyes.

Click on pictures to get notes

Index

Click on Boxes near the answers and know whether Your Answer is Correct or needs correction

Click- For Correct Answer You will hear

Click -For the incorrect answer You will hear

Click on Boxes near the answers and know whether Your Answer is Correct or needs correction

Click- For Correct Answer You will hear

Click -For the incorrect answer You will hear

Index

1 Spherical Mirrors are Portions of

2. Concave Mirrors have the silvered surfaces on the

Spherical Surfaces Plain Surfaces

Rough Surfaces None

Outer Side Inner Side

Both the Sides Top Side

Index

3. The geometrical centre of the concave mirror is

Radius Pole

FocusPlane

4. Centre of the sphere of which the mirror is a part is called

Centre of Curvature

Pole Radius of Curvature

Principal Focus

Index

5. The line passing through ‘Centre of Curvature’ and ‘Pole’ is known as

Radius of Curvature

Principal Axis None

Principal Focus

6. The Ray Parallel to Principal Axis ‘P’ is reflected through

Principal Focus ‘F’

None

The 2f

Between ‘F’ and ‘2f’

Index

Through ‘F’ itself

Parallel to Principal Axis

Through ‘C’

Through Principal Axis itself

Through ‘F’

8. The line passing through ‘C’ is reflected 24

On the Principal Axis Parallel to Principal Axis

Through ‘C’ itself

7. The line passing through ‘Principal Focus’ is reflected

Index

Formed Beyond ‘C’

Formed at ‘C’ Formed at infinity

Formed at ‘F’

9. When the object is between ‘F’ and ‘C’, the image is

10. The image is formed at infinity when the object is

At ‘P’

Between ‘F’ and ‘C’

At ‘C’

At ‘F’Index