Light can travel through a vacuum and enables us to see. It exhibits rectilinear propagation, reflecting regularly off smooth surfaces and irregularly off rough surfaces. Images can be real, formed by the actual intersection of light rays, or virtual, formed behind a mirror but not by the actual intersection of rays. Spherical mirrors can be concave or convex and have defined optical characteristics. Concave mirrors form enlarged images close to the mirror and diminished ones further away. Convex mirrors always form diminished, erect images. Lenses come in converging and diverging types and also have specific optical properties depending on the position of objects in relation to the focal point.

1. Light
Efforts by :- Aagman Saini

2. Light is a form of energy which enables us to see
everything around us. It does not require a medium and
can travel even in vacuum.
Introduction

3. The property of light travelling in straight lines in a
medium is known as rectilinear propagation of light.
Rectilinear propagation of light

4. The bouncing of light from a surface is called reflection.
Reflection of light is of two kinds :-
Regular reflection
Irregular reflection
Reflection of light

5. When the reflecting surface is smooth & well polished,
the light that falls on it is reflected regularly. This
phenomenon is known as regular reflection or specular
reflection.
Regular reflection

6. When the reflecting surface is irregular, the rays of light
that fall on it are scattered in all directions, it is known
as irregular reflection or diffused reflection.
Irregular reflection

7. There are two types of images:-
Real images
Virtual images
Types of images

8. A real image is formed by the actual intersection of light
rays & can be formed on the screen.
Real images
Real image

9. A virtual image is formed by the intersection of the light
rays when produced behind the mirror & not by their
actual intersection.
Virtual images
Virtual image

10. Spherical mirrors :- concave & convex
Plane mirror
Types of mirror

11.  The pole of a spherical is the centre (p) of the spherical
mirror.
 The centre of curvature of a spherical mirror is the centre
(c) of the sphere of which the mirror forms a part.
 The radius of curvature of a spherical mirror is the radius
(r) of the sphere of which the mirror forms a part.
 The principal axis of a spherical mirror is the line joining the
pole & the centre of curvature of the mirror.
Spherical mirrors

12. In a concave mirror, the image is erect & enlarged if the
object is very close to the mirror. Concave mirrors are
used as shaving mirrors & compact mirrors erect,
enlarged images of the face are formed.
concave mirror

13. In convex mirrors, the image is always erect &
diminished, at whatever distance the object may be in
front of the mirror. The convex mirror has a wide field
of view & hence is used as a rear view or driving mirror
in vehicles, to view the traffic behind.
Convex mirror

14.  Concave mirror are used as reflector in torchlight ,
shaving mirrors and compact mirrors.
Uses of concave mirror

15. Convex mirrors are used in :-
Rear view mirrors
Vigilance mirrors in stores
Uses of convex mirror

16. Images formed by spherical mirrors &
plane mirror
Nature of image Plane mirror Concave mirror Convex mirror
Size Same as object 1.Enlarged, when the object
is closer to mirror than C
2.Same size as the object,
when the objet is at c
3.Diminished when the
object is beyond c
Diminished for all
positions of the
object.
Real or Virtual Virtual 1.Virtual when the object
is within F
2.Real,for all other
positions of the object
Virtual for all positions of
the object
Distance from
the mirror
Same as the
object
As the object comes
closer to the mirror
Within F for all positions
of the object
inversion lateral 1.Erect when object is
within F
2.Inverted for all the
other positions of the
object
Erect

17. A lens is a piece of transparent material bound by
curved surfaces.
Lenses are of two types :-
 Lenses which are thicker in the middle than at the
edges are called convex lens(converging lens).
Lenses which are thinner in the middle than the edges
are called concave lenses(diverging lenses).
Types of lenses

18.  The principal axis is the line joining the centres of the two
spheres of which the lens forms a part.
 The optical centre is the centre of the lens(o).
 The principal focus (F) of a concave lens is a pointy of the
principal axis to which rays parallel axis converge after
refraction .
 The principal focus(F) of a concave lens is a point on the
principal axis from which rays parallel to the principal axis
appear to diverge after refraction.
 The focal length (f)of a lens is the distance between the
optical centre and principal focus.
lenses

19. Lens Object Location of the
image
Nature of the
image
Convex lens Beyond 2F
At 2F
Between F & 2f
Between F & O
Between F & 2F
At 2F
Beyond 2F
On the same side
Real, Diminished, Inverted
Real, small, inverted
Real, magnified, inverted
Virtual, magnified, erect
Concave lens All positions Within F on the
same side
Virtual,
diminished, erect
Images formed by lens

20. The famous scientist Isaac Newton showed that light is made of
seven colours.
The splitting of white light is known as dispersion.
The band of colours obtained because of dispersion of light is
called spectrum
The seven colours in the spectrum of white light are violet, indigo,
blue, green, yellow, orange & red (VIBGYOR).
Spectrum