This PowerPoint presentation is for Grade 10 students. I have included all the topics in this presentation. Here you can know about Light, Types of lenses, Some terms related to lens, Prism, Ray diagrams, Numerical problems related to this chapter, Laws of reflection, refraction, diseases related to eyes. I have briefly described as notes, some examples and illustrations, proper diagrams and so on.

1. CHAPTER 5
LIGHT
Light is a form of energy which produces
sensation of vision.

2. Lens
• Lens is a portion of transparent refracting
medium bounded by two spherical surfaces or
at least one surface is spherical.
• It is usually made up of glass or plastics.

3. Convex lens
• The lens which is thicker at the middle and
thinner towards each end is called convex
lens.

4. Types of convex lens

5. Convex lens is also called Conversing
Lens.
• Because it converses all the parallel beam of
light to a point called focus.

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7. Importances /Uses of Convex Lens
1. It is used in telescope , microscope ,
binoculars , etc.
2. It is used to correct far sightedness.

8. Concave lens
• The lens which is thinner at the middle and
thicker towards each end is called concave
lens.

9. Types of cancave lens

10. Concave Lens is also called Diversing
Lens.
• Because it diverses all the parallel beam of
light from a virtual point called focus.

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12. Importances /Uses of Concave Lens
1. It is used to correct short sightedness.
2. It is used in door to peep out of the door.

13. Some Terms Related to Lens

14. Centre of curvature(C): The centre of imaginary
sphere of which the curve surface is a part of
lens is called centre of curvature. C1 and C2 are
called centre of curvature.

15. Radius of curvature(R): It is the radius of the
sphere of which the surface forms the part of
the lens.

16. Principal axis(P): the straight line that joins the
centres of curvature of spheres that form a
lens is called principal axis.

17. Optical centre (O): the centre of lens is called
optical centre.

18. Principal focus (F): when parallel beam of light
falls on a lens , it either converses to a point
or appear to diverse from the point , the point
is called principal focus.

19. Focal length(f): the distance between optical
centre and principal focus of the lens is called
focal length.

20. Aperture: the diameter of the circular boundary
of the lens through which refraction takes
place is called aperture.

21. How to measure focal length of a
convex lens
Take ahand lens(magnifying glass) an hold it in
such a way that parallel rays of sun light could
pass through it. try to form the image of cloud
in the white paper or screen by focusing it.
focusing is the process of adjusting the focal
length of the lens by increasing or decreasing
the distance between lens and screen to
obtain clear image. When sharp image is
obtained, the distance between lens and the
screen gives focal length of that lens.

24. Action of Lens as a Set of Prism.

25. A lens may be considered to be made up of
sections of prisms, with a glass slab in the
middle.it is noticed that as we move towards
the edges of the lens, the angle of prism
increases. As the angle increases,the deviation
of the incident ray also increases.therefore, if
parallel beam of light falls on a prism,the ray
near the centre will be deviated the least and
the rays falling at the edges will be deviated
the most.

26. The action of lens is dependent on this
difference in deviation of the rays at the
centre and at the edges.

27. In the figure,in convex lens,
The rays are deviated
towards the centre and
meet at a point F.
Thus, a convex lens
converges a parallel
beam of light so that
all rays meet at a point.

28. In the figure,in concave lens,
The rays are deviated
away from the centre.
They appear to come
from a point F. Thus a
concave lens diverges
a parallel beam of light
so that all rays appear
to come from a point.

29. Rules For The Construction Of Ray
Diagram
1.The rays of light that fall on the lens passes
through the principal focus.

30. 2.A ray of light passing through the optical
centre of the lens emerges without any
deviation.

31. 3. A ray of light coming from principal focus
passes parallel with principal axis.

32. Ray Diagrams in Convex Lens

33. 1. When object is kept at infinity:

34. 2.When object is kept beyond 2F:

35. 3.When object is kept at 2F:

36. 4.Whe object is kept in between
F and 2F:

37. 5.When object is kept at F:

38. 6.When object is kept in between
principal focus(F) and optical centre(O):

39. Ray Diagram in Concave Lens:

40. 1.When object is kept at infinity:

41. 2.When object is kept in between
infinity and optical centre(O):

42. Power of Lens:
Power of lens is the reciprocal of its focal length
expressed in metre.it is also the ability of the
lens to converge or diverge the ray of light.
Power of lens(p)= 1/focal length(f)
SI unit of power of lens is Dioptre(D)

43. Example: 1. find power of lens if its focal length
is 20cm.

44. One Dioptre(1D):
Power of lens is one dioptre if its focal length is
one metre.
1D = 1/1m
1D = m-1

45. # The power of convex lens is positive because it
forms focus by intersection of actual rays .
So,focal length is positive and power is reciprocal
of focal length. So, it forms image by intersection
of real rays after refraction through the lens.
#The power of concave lens is negative because it
forms focus by intersection of virtual rays.so,
focal length is negative and power is reciprocal of
focal length. So, it forms image by intersection of
false rays after refraction through the lens.

47. Magnification(m):
The ratio of size of image(I) formed by a lens to
the size of object(O) is called magnification.
Magnification(m)= I/O

48. Also, it is the ratio of image distance(V) from a
lens to the object distance(U) in the same
lens.
Magnification(m)= V/U

49. Prove that: I/O = V/U

52. Human Eye

53. Power of Accommodation
• Ability of an eye to see far or near object
clearly by increasing or decreasing the focal
length of an eye lens is called power of
accommodation.

54. Persistence of vision
It is the condition of an eye in which the image
of an object remains for some tome in the eye
even the object is removed is called persistence
of vision. It is about 1/10part of a second.

55. Range of Normal vision:
Near point : 25cm
Far point : infinity
The nearest point from the eye at which an
object can be seen clearly by the eye is called its
Near point.
The farthest point from the eye at which
an object can be seen clearly by the eye is called
its Far point.
Range of distinct vision of eye is infinity to 25cm.

56. NORMAL EYE:
The eye which can see far or near object clearly
is called normal eye.

57. Normal eye

58. Defect of vision of eye:
The vision of an eye in which the eye can see
either near object only or far object only is
called defect of vision of the eye. There are two
types of defects of vision. They are :
1.Shortsightedness(Myopia)
2.Farsightedness(Hypermetropia)

59. Defect of vision of eye

60. Causes of shortsightedness/
Myopia
1.Decreasing of focal length of eye lens
2.Increasing of size of eyeball.

61. Correction of shortsightedness
(Myopia)
By using concave lens of suitable focal
length,myopia can be corrected.it is because
concave lens increases focal length and makes
image exactly on retina.

62. Correction of shortsightedness
(Myopia)

63. Causes of farsightedness/
Hypermetropia
1.Increasing of focal length of eye lens
2.Decreasing of size of eyeball.

64. Correction of farsightedness
(Hypermetropia)
By using convex lens of suitable focal
length,hypermetropia can be corrected.it is
convex lens decreases focal length of eye lens
and makes image exactly on retina.

65. Correction of farsightedness
(Hypermetropia)