Prepared By Senior Professor

1. PHYSICS
Propagation & Reflection Of Light

2. Light
• Light was considered as mysterious thing in
olden days.
• Light deals with luminous energy, energy
which causes the sensation of vision.
• Light is brightness that comes from an
object producing light , called luminous body
(sun).
• Light comes from atoms. Atoms that produce
light have either gained energy by absorbing
light from an other source or by being struck
by other particles. It is this extra energy that
causes an atom to give off light.
• Study of light and interaction of light and
matter is known as optics.

3. Properties of Light
Rectilinear propagation.
Shadow formation
Reflection.
Refraction.
Diffraction.
Dispersion.
Polarization.
Interference.

4. Properties of Light
Shadow Formation= The straight rays of light
passing the edges of non transparent( opaque) body,
leave a sharp shadow of that body in the way of light.

5. Properties of Light
Rectilinear Propagation= Light
travels in straight lines very fast.
Laser

6. Properties of Light
Reflection = when light strikes smooth shining
surface it returns back into same medium.
Incident ray Reflected ray
Normal

7. Properties of Light
Refraction = When light enters from
one transparent medium into another ,
it changes its path.

8. air
glass
normal
angle of
refraction
angle of
incidence
Properties of Light

9. Properties of Light
 Diffraction = It is apparent bending of light waves
around the obstacle in its path.

10. Dispersion = It refers to the break
down of white light( sun light) into its
constituent colours.
Properties of Light

11. Properties of Light
 Interference = It is the phenomenon that occurs
when two beams of light meet, to give brighter beam
(constructive interference) or to produce less bright
beam( destructive interference).

14. Properties of Light
Polarization= It is the direction, the wave is
vibrating in.

15. Plane-polarized waves
Plane-polarized waves
Circularly polarized waves

16. The reflection of Mount Hood in Mirror Lake.

18. Double reflection: The sun is reflected in the
water, which is reflected in the paddle.

19. Reflection Of Light
When light traveling through one medium
strikes the surface of another
medium(Mirror), part of it is returned back in
the first medium in a particular direction,
such phenomenon is called Reflection of
Light

20. Regular Reflection Or Specular
Reflection
 When rays of light strike the smooth shining surface
( plane mirror) they are reflected in the same
direction , it is called regular reflection. In it at
different places of surface, the values of incident
angle ( Li) are same.

21. Irregular Reflection Or Diffused
Reflection
 When rays of light strike rough surface(Earth), they
are reflected in different directions, it is called
irregular reflection. In it at different places of surface
the value of incident angle(Li) are not same.

23. Laws Of Reflection Of Light
 The incident ray, the reflected ray and the
normal all lie in the same plane.
 The angle of incident(li) is equal to the angle
of reflection (Lr).

26. Position & Nature Of Image Formed By Plane
Mirror
• In plane mirror image formed is of the same size as
the object.
• Image is as far behind the mirror as the object in
front of the mirror.
• Image is virtual and laterally inverted.

29. Applications Of Plane Mirror
• It is used as a looking glass.
• In the field of medicine, it is used by
Dentists and Ophthalmic surgeons.
• It is used in electric meters, in special
head lights, light microscopes,
periscope and kaleidoscope.

30. Applications Of Plane Mirror
As looking glass Periscope

31. Kaleidoscope Microscope

32. Applications Of Plane Mirror
Ophthalmoscope
Electric Meter

33. Applications Of Plane Mirror
Plane Mirror Head Light

34. Pin Hole Camera
 A pin hole camera is a simple camera without a lens and with
aperture , effectively alight - proof box with a small hole in one
side.
 Light rays from an object pas through a small hole to form an
inverted image , on semitransparent paper at the back of the
box. It is also known as camera obscura ( dark room).

35. Pin Hole Camera
Hole
Image
Semitransparent
paper
Object

36. Types Of Mirror
Plane Mirror Curved Mirror Parabolic Mirror

37. Spherical Mirror
• A mirror having curve surface is termed as
spherical mirror, being a part of large hollow
mirror) or curved mirror.

39. Types Of Spherical Mirrors
• Spherical mirrors are classified into
following two types, according to how they
reflect light rays from a distant source.

40. Terms Used In Spherical mirror
 CP = Radius of curvature.
 C = Centre of curvature.
 PO = Principal axis.
 P = Pole of mirror.
 F = Focus of mirror.
 PF(f) = focal length of mirror.
 XY = Aperture of mirror.

43. Concave Mirror
Its reflecting surface caves inwards.
It is converging mirror.
It forms real image.
Its focal length is taken positive ( +ve ).

44. Convex Mirror
Its reflecting surface bulges
outwards.
It is diverging mirror.
It forms virtual image.
Its focal length is taken negative (-ve ).

45. Uses Of Spherical Mirrors
Concave Mirrors=(1)These are used in
search light, head light and flash
light.(2)These are used as objective in
Reflecting Telescopes.
(3) These are used as magnifiers.(4) These are
used in solar heaters.

46. Reflecting Telescope
Uses Of Concave Mirror

47. Uses Of Concave Mirror
Head Lights
As Magnifier

48. Uses Of Spherical Mirrors
Convex Mirror = These having vast
field vision are used as side mirrors in
motor vehicles.

49. Uses Of Spherical Mirrors

50. Rules For Light Rays In concave
Mirror
A. The ray of light C,this is reflected back
through C.
B. The ray of light parallel to the principal axis,
is reflected through F.
C. The ray of light through F, is reflected
parallel to the principal axis.

53. Ray diagrams

54. Description Of An Image
To describe an image, fallowing four aspects
need to be determined.
 Its location = Where it is in relation to the mirror.
 Its size =How big it is compared with the object.
 Its orientation = Where it is upright or upside down.
 Its nature = Where or not the image can be captured
on a screen.

57. Images Formed By concave Mirror
I. If object is placed beyond C.Its image will
be formed near F ( out side the focus of
mirror) the focus of mirror. Image will be
real, inverted and smaller than the object.

58. II. If object is placed at C .Its image will be
formed at C.image will be real, inverted and
of same size as object.
Images Formed By concave Mirror

59. Images Formed By concave Mirror
III.If object is placed b/w C and F. its image will
be formed out side the C. Image will be real,
inverted and larger than object.

60. Images Formed By concave Mirror
IV. If object is placed inside the focus(F). Its
image will be formed behind the mirror.Image
will be virtual, upright and magnified.

61. Difference B/W Real & Virtual Image
Real Image
• In it rays of light
actually pass
through it.
• It can be obtained
on screen.
• Its distance is
shown with +ve
sign.
• It is inverted.
Virtual Image
a) In it rays appear
coming from the
place of image.
b) It is only visible to
eye and can not be
obtained on
screen.
c) Its distance is shown
with –ve sign.
d) It is upright.

62. Magnification & Sign Conventions For spherical
Mirrors
 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 mirror & image (q ) is taken +ve.
 Distance b/w convex mirror & image is taken –ve.
 Focal length of concave mirror ( f ) is taken +ve.
 Focal length of convex mirror is taken –ve .

63. Mirror Equation ( Concave Mirror)
Δ ABC and Δ OIC are similar.
AB/OI = BC/IC = p/q……………(i)
ΔABF and Δ FCD are similar.
AB/DC = BF/FC = BC – FC / FC = p - f / f……………..(ii)

64. Mirror Equation ( Concave Mirror)
Comparing I & ii
p/q = p – f / f B.C.M pf = pq – fq……….(iii)
Dividing both the sides of Eq:III with pqf.
Pf/pqf = pq/pqf = fq/pqf.
1/q = 1/f – 1/p or 1/f – 1/p = 1/q.
1/f = 1/p + 1/q( Mirror Equation).