# and Principal by alicejenny

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```									Images Formed by a
Concave Mirror

VII std Science
(State Syllabus)
Project Done by:

B. Dhandapani
Teacher Educator
Block Resource Centre
Sarva Shiksha Abhiyan
Mannargudi Block
Thiruvarur District
Email bdpani@rediffmail.com
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’
study the relevant topic
Object between ‘F’ and ‘C’
Object at ‘F’
Object between ‘P’ and ‘F’
All in One
Relative Movement of the Object and the Image
Uses of Concave Mirrors
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
Terms Used in Spherical Mirrors

Pole (P)                           (C) Centre of Curvature
Geometrical                               Centre of the
Centre                                    sphere of which the
mirror is a part

The Line Passing through C,P – Principal Axis

P – Pole
C – Centre of Curvature
Index                   Principal Axis
Index
Construction 1

Ray Parallel to Principal Axis

F             Principal Axis

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

Index
Construction 2

F             Principal Axis

Ray Passing through ‘F’

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

Index
Construction 3

F         C           Principal Axis

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
1

F           C

2

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.

Index
1

2

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

Index
2
1

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.

Index
2
1

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.

Index
1

2

P         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.

Index
…All in One (Recap)
Object @ Infinity – Image @ ‘F’ – Real, Inverted
Object beyond ‘C’ – Image between ‘F’ & ‘C’- Real, Inverted

Object

P                                            Infinity

F         C

Image

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

Index
Object

Image

When the Object moves closer to the Mirror,

The Image Moves away from the Mirror
Index
Index
SlNo      Place of       Place of the         Rays to be Drawn      Nature of the
the Object     Image Formed                                   Image

All Rays Parallel to     Real, Inverted,
1       At Infinity   At ‘F’              Principal Axis (PA)      Small

Ray 1 Parallel to PA &   Real, Inverted,
2       Beyond ‘C’    Between ‘F’ & ‘C’   Ray 2 Through ‘C’        Small

Ray 1 Parallel to PA &   Real, Inverted,
3       At ‘C’        At ‘C’              Ray 2 Through ‘F’        Same as
Object

Ray 1 Parallel to PA &
4       Between ‘F’   Beyond ‘C’          Ray 2 Through ‘C’        Real, Inverted,
& ‘C’                                                      Large

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

At the Back of      Ray 1 Parallel to PA &   Virtual, Large,
6       Between ‘F’   the Mirror          Ray 2 Through ‘C’        Straight
& ‘C’
Used in mirror telescopes
(its front is a silver-plated mirror)

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

•The spherical concave mirror finds its
most valuable application as eye mirror
(Helmholtz 1851). It serves during               Click on
examination of the inside of eyes.
pictures to
get notes
Index
Click on    Boxes near the answers and
needs correction
Click- For Correct Answer You will hear
Click -For the incorrect answer You will
hear

Index
1 Spherical Mirrors are Portions of

Plain Surfaces                 Spherical Surfaces

Rough Surfaces                 None

2. Concave Mirrors have the silvered surfaces on the

Outer Side                      Inner Side

Both the Sides                  Top Side

Index
3. The geometrical centre of the concave mirror is

Focus
Plane

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

Centre of Curvature           Principal Focus

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

Principal Axis                   None

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

The 2f                          Principal Focus ‘F’

Between ‘F’ and ‘2f’            None

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

Through ‘F’ itself            Through ‘C’

Parallel to Principal Axis    Through Principal Axis itself

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

Through ‘C’ itself            Through ‘F’

Parallel to Principal Axis    On the Principal Axis
Index
9. When the object is between ‘F’ and ‘C’, the image is

Formed at ‘C’               Formed at infinity

Formed at ‘F’                Formed Beyond ‘C’

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

At ‘P’                      At ‘C’

At ‘F’                      Between ‘F’ and ‘C’
Index

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