Notes by Madhu mam

1. Light - Reflection
and Refraction
Class10Science
Full Chapter

2. I n t r o d u c t i o n
Light - It is a form of energy which produces us the sensation of vision.
Source - A source of light is an object, from which light is given out. Some
sources of light are natural and many others are man-made sources.
Ray - A ray of light is the straight line path along which light travels.
Mirror is a shiny polished object (glass) which reflects most of the rays of
light falling upon it.
A number of rays combined together form a beam of light.

3. → Electromagnetic wave, so does not require any medium to travel.
→ Light tends to travel in straight line.
→ Light has dual nature i.e. wave as well as particle.
→Light casts shadow.
→Speed of light is maximum in vaccum. Its value is 3 × 10 m/s.
8
P r o p e r t i e s o f L i g h t

4. Spherical Mirror
➤ Concave
➤ Convex
Types of Mirror
Plane Mirror

5. Convex Concave

6. Reflection of Light (Plane mirror)
Reflection of light is the phenomenon of bouncing back of
light in the same medium on striking the surface of any object.

7. Laws of Reflection
Angle of Incidence = Angle of Reflection ( ∠i = ∠r )
The incident ray, reflected ray and the normal lie in the same plane.
These laws of reflection are applicable to all types of reflecting
surface including spherical surfaces.

8. An image may be defined as that
point, where the light rays coming
from an object meet or appears to
meet after reflection or refraction.
What's an Image ?

9. Virtual and Real Images

10. Image formed by Plane mirrors
Characteristics/Nature of Image :
Size of the image is same as the size of the object.
The image obtained is virtual.
The image is laterally inverted.
The image is erect.
The distance between the image obtained is the
same as the distance between the object from the
mirror.

11. Ray Diagram :

12. Spherical
Mirrors

13. Convex mirrors
Concave mirrors
→Mirrors whose reflecting surface is curved.
→They are two types of spherical mirrors :
S p h e r i c a l m i r r o r s

14. Properties of Convex mirrrors :
Reflecting surface is curved outwards.
Diverging mirror
1.
2.
Properties of Concave mirrrors :
Reflecting surface is curved inwards.
Converging mirror
1.
2.

16. →Principal axis
→Pole (P)
→Aperture (MN)
→Center of Curvature (C)
Common terms for Spherical mirrors
→Radius of Curvature (R)
→Focus (F)
→Focal length (f)
→Relationship between focal length
and radius of curvature: f = R/2
M
N

17. Representation of Images formed by Spherical mirrors
(i) A ray parallel to the principal axis, after reflection, will pass through the
principal focus in case of a concave mirror or appear to diverge from the
principal focus in case of a convex mirror.

18. (ii) A ray passing through the principal focus of a concave mirror or
a ray which is directed towards the principal focus of a convex
mirror, after reflection, will emerge parallel to the principal axis.

19. (iii) A ray passing through the centre of curvature of a concave mirror
or directed in the direction of the centre of curvature of a convex
mirror, after reflection, is reflected back along the same path.

20. (iv) A ray incident obliquely to the principal axis, towards a point
P (pole of the mirror), on the concave mirror or a convex mirror,
is reflected obliquely.

21. Image formation by Concave mirror
(i) When the object is at infinity
→Image Position - At the Focus (F)
→Nature of the Image - Real and Inverted
→Size of the Image - Highly diminished

22. (ii) When the object is beyond 'C'
→Image Position - Between 'C' and 'F'
→Nature of the Image - Real and Inverted
→Size of the Image - Diminished

23. (iii) When the object is at 'C'
→Image Position - At 'C'
→Nature of the Image - Real and Inverted
→Size of the Image - Same size as that of the object

24. (iv) When the object is placed between 'F' and 'C'
→Image Position - Beyond 'C'
→Nature of the Image - Real and Inverted
→Size of the Image - Enlarged

25. (v) When the object is placed at 'F'
→Image Position - At Infinity
→Nature of the Image - Real and Inverted
→Size of the Image - Highly Enlarged

26. (vi) When the object is between 'P' and 'F'
→Image Position - Behind the mirror
→Nature of the Image - Virtual and Erect
→Size of the Image - Enlarged

28. Image formation by Convex mirror
(i) When the object is at infinity
→Image Position - At the Focus (F), behind the mirror
→Nature of the Image - Virtual and Erect
→Size of the Image - Highly diminished

29. (ii) When the object is placed between infinity and pole
→Image Position - Between 'P' and 'F', behind the mirror
→Nature of the Image - Virtual and Erect
→Size of the Image - Diminished

31. Uses of Concave Mirrors
Used in torches, search lights and vehicles headlights to get
powerful parallel beam of light.
Concave mirrors are used by dentists to see large image of teeth
of patients.
Concave mirror is used as shaving mirror to see a larger image of
the face.
Large concave mirrors are used to concentrate sunlight to
produce heat in solar furnace.

32. Uses of Convex Mirrors
(i) Convex mirrors are used as rear view mirrors in vehicles because
→they always give an erect though diminished image.
→they have a wider field of view as they are curved outwards.
(ii) Convex mirrors are used at blind turns and on points of merging
traffic to facilitate vision of both side traffic.
(iii) Used in shops as security mirror.

33. Concave

34. S i g n c o n v e n t i o n f o r R e f l e c t i o n b y S p h e r i c a l M i r r o r s
New Cartesian Sign Convention
While dealing with the reflection of light by spherical mirrors, we shall
follow a set of sign conventions called the New Cartesian Sign Convention
The Conventions are as follows :
(i) The object is always placed to the left of the mirror. This implies that
the light from the object falls on the mirror from the left-hand side.
(ii) All distances parallel to the principal axis are measured from the pole
of the mirror.

35. (iii) All the distances measured to the right of the origin (along + x-axis)
are taken as positive while those measured to the left of the origin
(along – x-axis) are taken as negative.
(iv) Distances measured perpendicular to and above the principal axis
(along + y axis) are taken as positive.
(v) Distances measured perpendicular to and below the principal axis
(along –y-axis) are taken as negative.

37. → Mirror Formula ( Spherical Mirrors)
1
v
1
u
1
v
+ =
'v' = image distance
'u' = object distance
'f' = focal length

38. Magnification
Magnification is defined as the ratio of the height of the image to the
height of the object.
Height of image ( h' )
Height of object ( h )
m =
h'
h
m =
-v
u
=

39. The phenomenon of change in the path of light in going from
one medium to another is called refraction of light.
The basic cause of refraction is the change in the speed of
light in going from one medium to another.
Speed of light is maximum in vacuum. It is 3 X 108 m/s.
Refraction of Light

40. Some examples of Refraction of Light :-
• The bottom of swimming pool appears higher.
• A pencil partially immersed in water appears to be bent
at the interface of water and air.
• Lemons placed in a glass tumbler appear bigger.
• Letters of book appear to be raised when seen through a
glass slab.

41. 2. When a ray goes from e
d denser to rarer medium.
1. When a ray goes from e
d rarer to denser medium.

42. Refraction Through a Rectangular Glass Slab

43. Laws of Refraction
• The incident ray, the refracted ray and the normal to the
interface of two transparent media at the point of incidence,
all lie in the same plane.
• The ratio of the sine of the angle of incidence to the sine of the
angle of refraction is a constant, for the light of a given colour
and for the given pair of media. This law is also known as
Snell’s law of refraction.
𝐬𝐢𝐧 𝒊
𝐬𝐢𝐧 𝒓
= constant

45. Refractive Index
It represents the amount or extent of bending of light when it
passes from one medium to another.
There are two types of refractive index :-
• Relative refractive index
• Absolute refractive index

46. Relative Refractive Index – When light travels from one medium 1
to another medium 2 the refractive index of medium 2 with
respect to medium 1 is given by the ratio of speed of light in
medium 1 and the speed of light in medium 2.
The refractive index of medium 1 with respect to medium 2.
n21 =
𝑺𝒑𝒆𝒆𝒅 𝒐𝒇 𝒍𝒊𝒈𝒉𝒕 𝒊𝒏 𝒎𝒆𝒅𝒊𝒖𝒎 𝟏
𝑺𝒑𝒆𝒆𝒅 𝒐𝒇 𝒍𝒊𝒈𝒉𝒕 𝒊𝒏 𝒎𝒆𝒅𝒊𝒖𝒎 𝟐
=
𝑽𝟏
𝑽𝟐
n12 =
𝑺𝒑𝒆𝒆𝒅 𝒐𝒇 𝒍𝒊𝒈𝒉𝒕 𝒊𝒏 𝒎𝒆𝒅𝒊𝒖𝒎 𝟐
𝑺𝒑𝒆𝒆𝒅 𝒐𝒇 𝒍𝒊𝒈𝒉𝒕 𝒊𝒏 𝒎𝒆𝒅𝒊𝒖𝒎 𝟏
=
𝑽𝟐
𝑽𝟏

47. Absolute Refractive Index :- The refractive index of one
medium with respect to vacuum or air is known as an absolute
refractive index.
nm =
𝑺𝒑𝒆𝒆𝒅 𝒐𝒇 𝒍𝒊𝒈𝒉𝒕 𝒊𝒏 𝒂𝒊𝒓
𝑺𝒑𝒆𝒆𝒅 𝒐𝒇 𝒍𝒊𝒈𝒉𝒕 𝒊𝒏 𝒎𝒆𝒅𝒊𝒖𝒎
=
𝐜
𝐯

48. Refraction of light by Spherical lens :-
Spherical lens :- A transparent medium bound by two
surfaces, of which one or both surfaces are curved is
called a spherical lens.
Concave lens :- It is a spherical lens in which
two spherical surfaces bulge inwards. It is
also called diverging lens.
Convex lens :- It is a spherical lens in which
two spherical surfaces bulge outwards. It is
also called converging lens.

49. Concave lens
Convex lens

50. (i) A ray of light from the object, parallel to the principal axis, after
refraction from a convex lens, passes through the principal focus on the
other side of the lens. In case of a concave lens, the ray appears to diverge
from the principal focus located on the same side of the lens.
Rules for Refraction of rays by Spherical Lens

51. (ii) A ray of light passing through a principal focus, after refraction from a
convex lens, will emerge parallel to the principal axis. A ray of light
appearing to meet at the principal focus of a concave lens, after refraction,
will emerge parallel to the principal axis.

52. (iii) A ray of light passing through the optical centre of a lens
will emerge without any deviation.

53. (i) When the object is at infinity
→ Image is formed at focus F2
→ Image is highly diminished or point-sized
→ Image is real and inverted
Image formation by Convex Lens

54. (ii) When the object is beyond 2F1
→ Image is formed between F2 and 2F2
→ Image is diminished
→ Image is real and inverted

55. (iii) When the object is at 2F1
→ Image is formed at 2F2
→ Image is same size as that of object
→ Image is real and inverted

56. (iv) When the object is between F1 and 2F1
→ Image is formed beyond 2F2
→ Image is enlarged
→ Image is real and inverted

57. (v) When the object is at focus F1
→ Image is formed at infinity
→ Image is infinitely large or highly enlarged
→ Image is real and inverted

58. (vi) When the object is between focus F1 and optical centre O
→ Image is formed on the same side of the lens as the object
→ Image is enlarged
→ Image is virtual and erect

60. (i) When the object is at infinity
→ Image is formed at focus F1
→ Image is highly diminished or point sized
→ Image is virtual and erect
Image formation by Concave Lens

61. (ii) When the object between infinity and optical centre O of lens
→ Image is formed between focus F1 and optical centre O
→ Image is diminished
→ Image is virtual and erect

63. Lens Formula
𝟏
𝒗
-
𝟏
𝒖
=
𝟏
𝒇
Magnification
m =
𝒉′
𝒉
=
𝒗
𝒖

64. P =
𝟏
𝒇
→ The SI unit of power is dioptre (D).
→ Power of convex lens is positive.
→ Power of concave lens is negative.
Power of a Lens

65. Chapter Finished !!
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