1. PHYSICS
Refraction Of Light

2. Refraction Of Light
• When a ray of light , travelling through one medium
strikes obliquely the surface of an other transparent
medium, then there is change in its direction in the
second medium. This change is called Refraction of
light.
• Light refracts at boundary( b/w two mediums )
because of change in its speed.

4. Refraction Of Light
• If ray of light enters from rare into denser medium it
bends towards the normal. But when enters from
denser into rare medium, it bends away from the
normal.

5. air
glass
• e.g. from air to glass
• Light is bent towards the normal.
normal
From a less dense to a denser medium

6. air
water
From a denser to a less dense medium
• e.g. from water to air
• Light is bent away from the normal.
normal

7. air
glass
Useful words to describe refraction of light
normal
angle of
refraction
angle of
incidence

8. Laws Of Refraction Of Light
 Incident ray, refracted ray and normal lie in the same
plane.
 The ratio of sine of angle of incident to the sine of
angle of refraction is constant in any two transparent
mediums, which is termed refractive index (n).
Refractive index (n) =sin Li/Sin Lr = Constant

10. Angle of Incidence (degrees) Angle of Refraction (degrees)
0.00 0.00
5.00 3.8
10.0 7.5
15.0 11.2
20.0 14.9
25.0 18.5
30.0 22.1
35.0 25.5
40.0 28.9
45.0 32.1
50.0 35.2
55.0 38.0
60.0 40.6
65.0 43.0
70.0 45.0
75.0 46.6
80.0 47.8
85.0 48.5

12. Refraction of light

13. Refractive index and speed
of light
vacuum (or air)
3  108 m
water (n = 1.33)
2.25  108 m
glass (n = 1.5)
2  108 m
diamond (n = 2.42)
1.25  108 m
Refractive index
Speed of light
fastest
slowest

14. Refractive Index (n) Of Different Materials

15. Prism
• It is transparent body (Glass) ,
commonly having three sides
rectangular and two sides triangular.

16. Refraction Of Light Through Prism
• Incident ray PQ strikes side AB of prism. Inside
prism the ray in shape of refracted ray QR, bends
towards the normal XY . Then emergent ray RS
coming from prism bends away from the normal LM.

17. Refractive Index Of Glass Prism (nG)
• (nG)=
Sin (A + Dm)
2
Sin A
2
LA = Angle of prism.
LDm = Angle of minimum deviation.
nG = Refractive index of glass
prism

18. Refraction of light through prism

19. Total Internal Reflection
 If ray of light passes from a denser medium(
water ) into a rare medium (air ) then it bends
away from the normal.
 Now increasing the angle of incidence,
angle of refraction also increases.

20. Total Internal Reflection
 At certain stage the angle of incidence has increased
so much that the corresponding value of angle of
refraction becomes equal to 90o and refracted ray
lies on the surface of denser medium.
 The angle of incidence for which the angle of
refraction is 90o is called the critical angle.

21. Total Internal Reflection
 Now if the value of angle of incidence is increased
so much that it becomes greater than critical angle,
then there is no more refraction but whole of it is
reflected back in the denser medium.
 Such reflection of light is called total internal
reflection.

24. Optical Fibres
• These are very thin, flexible glass rods, used
for carrying light by total internal reflection
from one end to other end. A bundle of
optical fibres is called light pipe.

25. Optical Fibres
• The glass cladding of slightly lower refractive index
than that of the core, prevents surface damage to the
core fibre, otherwise would allow light to escape.

28. Optical Fibres (uses)
• Big advantage of an optical fibre is its
small size and weight.
• Optical fibres are successfully used in
internal surgery to examine body cavities
and in telecommunication.

29. Lens & Its Kinds
LENS = It is a transparent body(glass),
bounded by one or two Curve surfaces.
KINDS OF LENS = there are two kinds of lens
(a) Convex Lens & (b) Concave Lens

32. Convex Lens
 It is thickest in the centre, because its
boundaries are curving outwards.
 As it bends light inwards( rays come
together), hence it is also called Converging
lens.
 Its focal length is taken +ve.
 It forms real image.

33. Double convex lens behaves like two prisms with attached bases.

35. Concave Lens
 It is thinnest in the centre, because its
boundaries are curving inwards.
 As it spreads light out( rays move apart),
hence it is also called a diverging lens.
 Its focal length is taken –ve.
 It forms virtual image.

38. Uses Of Lenses
Convex lens is used in
camera,projectors,binocular,telescope,
microscope,spectacle and as magnifier
etc.
Concave lens is used in spectacle for
removing eye defect.

39. Convex Lens Used As Magnifier

40. Astronomical Telescope
Camera Compound microscope
Spectacle
Binocular

41. Film Projector
Slide Projector
Over Head Projector

42. Images Formed By Convex Lens

43. Images Formed By Convex Lens

44. Magnification & Sign Conventions For Lenses
 Optical magnification is the ratio between the size of image &
size of object.
M = hi = q
ho p
 M = Magnification, hi = Height of image , ho = Height of
object.
 Distance b/w concave lens & image (q ) is taken - ve.
 Distance b/w convex lens & image( q ) is taken + ve.
 Focal length of concave lens ( f ) is taken - ve.
 Focal length of convex lens( f ) is taken + ve .

46. Power Of Lens
 Power of lens is the reciprocal of the focal length
expressed in meters.
 Power = 1 Or P = 1
focal length (in m ) f
 The unit of refractive power of a lens is the diopter(
where 1 diopter = !/meter ).
 Converging lens has a positive power and diverging
lens has a negative power.
 One diopter is the power of lens of focal length one
meter.
 A Powerful lens deviates light rays more and thus
has a short focal length.
 Magnifying glass( of f=2cm) has power
diopters,while high power microscope objective(of
f= 4mm) has power 250 diopters.

47. Human Eye
In eye image is formed on retina.
In it amount of light entering into eye is
controlled by Iris.
For correct and clear image ( of near or
far objects) the thickness of eye’s lens
is increased or decreased by ciliary
muscles.

48. Structure Of Human Eye

49. Short- Sightedness(Myopia)
 Definition = In this defect of vision an eye
can see clearly only near objects,
 Reason = the lens of eye becomes too much
convergent, or eye ball becomes too long. So
the images of distant objects is formed in
front of the Retina.
 Remedy = For correcting this defect
concave lens ( diverging lens) of suitable
focal length is used.

53. Long- Sightedness (Hyperopia )
 Definition =In this defect of vision, an eye
can see clear only distant objects.
 Reason = the lens of eye becomes less
convergent or eye ball becomes too short.
 Remedy = for removing this defect convex
lens(converging lens) of suitable focal length
is used.

55. Contact Lens

56. Astronomical Telescope
 It is used to see far objects near and clear
 In it the focal length of object lens is long and focal
length of eye piece is short.
 Objective lens forms real inverted image before eye
piece, which forms its magnified ,virtual image

57. Astronomical Telescope

58. Enlarged –
Image is larger
than actual
object.
Reduced –
Image is smaller
than object

59. Compound Microscope
It is used to see minute near object clear and
magnified.
In it the focal length of objective lens is short and
focal length of eye piece is long.
Objective lens forms, enlarged ,inverted image,
eye piece forms its further enlarged, virtual
image.

60. Compound Microscope

61. Camera
In it image is formed on sensitive
film.
Light reaching the film is
controlled by shutter and also by
diaphragm.
For getting correct and clear
image, convex lens is moved
forward or backward.

62. Slide Projector

63. Camera

64. Lens Equation ( Convex Lens )
[As BD= p,DF= f & DI = q.]
As Δ OID and Δ ABD are similar
AB/OI = BD/DI……………….(I)
AS Δ CDF and Δ OIF are similar
CD/OI = DF/IF
As CD = AB
Then AB/OI = DF/IF ……………(II)

65. Lens Equation ( Convex Lens )
[As BD= p,DF= f & DI = q.]
As Δ OID and Δ ABD are similar
AB/OI = BD/DI……………….(I)
AS Δ CDF and Δ OIF are similar
CD/OI = DF/IF
As CD = AB
Then AB/OI = DF/IF ……………(II)
comparing I and II we get.
BD/DI = DF/IF or BD/DI = DF/DI –DF……………….(III)
Put value of BD,DF and DI in equation III we get
p/q =f/q-f B.C.M we get pq- pf = qf or pq=qf+ pf.
Dividing both sides of above Equation by pqf we get
pq/pqf = qf/pqf + pf/pqf
1/f = 1/p + 1/q (Lens Equation)