CHAPTER 5 : LIGHT
Reflection Of Light
Light
Mirrors Lenses
Plane
Convex mirror
Concave mirror
Convex lens
Reflection Refraction
Concave lens
Lenz Law
Total internalreflection
• Light is a form energy that enables us to see.
• Light is emitted or given by hot objects, like a candle flame, or the glowing filament of light bulb, or the sun.
• An object which produces its own light is said to be luminous.
• Most of the objects we can see do not produce their own light – they are non-luminous. What we can see is the light is reflected off them. Example like cloths, rock, face and etc.
Reflection Of Light
Reflection Of Light• Light seems to travel in straight lines.
A picture of light as rays traveling in straight lines from a luminous source or bouncing off objects, or being absorbed or transmitted by them, is very useful one.
Reflection Of Light• We can think of light ray as a very
thin beam of light. A real beam contains many rays. But by drawing just a few of them we can get a clear idea of what happening to the whole beam.
Reflection Of Light• When rays of light strike any surface the
rays are reflected , unless the surface is black, when they are absorbed.
Reflection Of Light• The reflection depend on how smooth the
surfaces are. Good mirrors reflect well over 90% of the light that reaches them, with only a small amount being absorbed.
• The surface of most objects are very irregular. Light hitting this sort of surface is scattered in all directions. This is called diffuse reflection.
• On the other hand, the surface of a polished sheet of glass or metal can be made extremely smooth. The reflection from this is the regular.
mirror
Most objects
Regular reflection
Difuse reflection
Example reflection of light
Example reflection of light
Incident ray Reflected ray
i r
i = r
Laws of reflection of light:
1. Incident angle = reflected angle
2. The incident ray, the normal and the reflected ray all lie in the same plane
Reflection Of Light
AO : Incident ray
ON : Normal Line
OB : Reflected ray
i : Angle of incidence
r : Angle of reflection
Reflection Of LightCommon terminology of reflection of light on a plane mirrorNormal Line, N :A line at right angles to the mirror’s surface.
Incident ray, i :A ray of light that is directed onto the mirror’s surface.
Reflected ray ,r :A ray that is reflected by the mirror’s surface.
Reflection Of LightAngle of incidence, i :
The angle between the
incident ray and the
Normal
Angle of reflection, r :
The angle between the
reflection ray and the
normal line
i rPlane mirror
N
Laws of Reflection
The Law Of Reflection State That:
• The incident ray, the reflected ray and the normal to the point of incidence, all lie in the same plane.
• The angle of incidence, i = The angle of reflection, r
Mirror
1. Plane Mirror
2. Curved mirror
– Concave mirror ( Cermin Cekung )
– Convex mirror (Cermin Cembung)
Characteristics of the image
Same size as the object
Virtual
Laterally inverted
Image formed by a plane mirror:
object
i1r1
A B C
Eye
Image
Characteristics of image formed by plane mirror:
Characteristics of image formed by plane mirror:
i ) virtual
ii) laterally inverted
iii) same size as object
iv) object distance from mirror
= image distance from mirror
v) Upright
Differences between real and virtual image:
Real image Virtual image
Can be appear on a screen
Cannot be appear on a
screen
Formed by the meeting of real
rays.
Form at a position where rays appear to be originating.
Example LCD Projector
Example Image from mirror
45o
100o
45o
45o
35o 55o
55o
Curved Mirror
• Concave mirror ( Cermin Cekung )
• Convex mirror (Cermin Cembung)
Common terminology of reflection of light on a curved mirror
PC
r
Concave mirror
C
r
P
Convex mirror
CF
Convex Mirror
C
F
Concave Mirror
C = Centre of curvature
r = Radius of curvature
P = Pole
PC = Principal axis
PC
r
Concave mirror
C
r
P
Convex mirror
Concave mirrorPole of mirror , P :
The centre point on
the curved mirror
Centre of curvature , C
:The geometric centre
of a hollow sphere of
which the concave or
convex mirror is a part.
Concave mirror
Principal axis ,PFC
: A line which passes
through the centre of
curvature ,C and the
pole of a curved
mirror, P
Concave mirrorPrincipal focus , F
A point where all rays
traveling parallel to the
principal axis converge or
diverge after reflection
by the mirror.
Radius of curvature, r :
Distance between the
pole, P and the
centre of curvature, C
Concave mirror
• Focal length , f
: The distance
between the principal
focus ,F and the pole of
the curved mirror, P.
Convex mirrorPole of mirror , P
: The centre point on
the curved mirror
Centre of curvature , C
: The geometric centre
of a hollow sphere of
which the concave or
convex mirror is a part.
Convex mirror
Principal axis ,PFC
: A line which passes
through the centre of
curvature ,C and the
pole of a curved
mirror, P
Convex mirrorPrincipal focus , F
: A point through
which all rays traveling
parallel to the principal axis
converge to or appear to
diverge from after reflection
by the mirror.
Radius of curvature, r
: Distance between
the pole, P and the
centre of curvature, C.
Convex mirror
Focal length , f
: The distance
between the principal
focus ,F and the pole of
the curved mirror, P.
Relationship between f and r
r = 2f = PC
PF = FC
f1 f2
f1 < f2
Relationship curvature of mirror and f
The more curved the
mirror , the shorter its
focal length, f.
Image formed by curved mirror (ray diagram method)
Principle of drawing ray diagrams:
1. The position and characteristics of images formed by a concave or convex mirror can be determined by drawing ray diagrams.
2. Images formed by concave or convex mirror can be determine by drawing two of the following rays. A curved mirror is represented by a straight line.
C F
Image formed by a Concave Mirror
F = Focal point C = Centre Of mirror
Case 1: u < f
C FF
object
Concave mirror
image
Characteristics Of Images : Upright, Virtual , enlarged
Case 2: u = f
Characteristics Of Images :
C F
Case 2: u = f
C FF
object
Concave mirror
Characteristics Of Images : Enlarged, Virtual , Upright
Case 3: f < u < 2f
Characteristics Of Images :
C F
Case 3: f < u < 2f
C FF
object
Concave mirror
image
Characteristics Of Images : Enlarged , Inverted , Real
Case 4: u = 2f or u = r
C F
Case 4: u = 2f or u = r
C FF
object
Concave mirror
image
Characteristics Of Images : Same Size , Inverted , Real
Case 5: u > 2f
Case 5: u > 2f
Characteristics Of Images : Diminished In Size , Inverted ,Real
C F
Case 6 u = ( Object ,O very far from the lens)
Case 6 u = ( Object ,O very far from the lens)
Characteristics Of Images : Real , Inverted , Diminished In Size
Conclusion Concave Mirror
The distance object, u Characteristics of image
u < f
u = f
f <u < 2f
u = 2f
u > 2f
u = Conclusion
C F C F
C F C F
C F
Figure Characteristic of image
P
Q
R
S
T
Virtual, Upright, Magnified
Virtual, Upright, Magnified
Real, Inverted, Magnified
P
T
SR
Q
Real, Inverted, Same size
Real, Inverted, Diminished
VUM VUM
RIM RIS
RID
Conclusion Concave Mirror The distance object, u Characteristics of image
u < f Upright, Virtual , magnified
u = f Magnified, Virtual , Upright
f <u < 2f Magnified , Inverted , Real
u = 2f Same Size , Inverted , Real
u > 2f Diminished In Size, Inverted , Real
u = Real , Inverted , Diminished In Size
Conclusion
C F
Image formed by a Convex Mirror
1) u < f ( Object between F and P )
Characteristics of image :
Image formed by a Convex Mirror
1) u < f ( Object between F and P )
Characteristics of image : Virtual, Upright , Diminished In Size
2) f < u < 2f or f < u < C ( Object O is between F and C.)
Characteristics of image :
2) f < u < 2f or f < u < C ( Object O is between F and C.)
Characteristics of image : Diminished In Size, Upright, Virtual
3) u > 2f (Object, O is beyond C)
Characteristics of image :
3) u > 2f (Object, O is beyond C)
Characteristics of image : Diminished In Size, Upright, Virtual
Conclusion Convex Mirror
The distance object, u
Characteristics of image
u < f
f < u < 2f
u > 2f
Conclusion
F C
F C F C
Figure Characteristic of image
X
Y
Z
X
Z
Y
Conclusion:
Upright, diminished, virtual
Upright, diminished, virtual
Upright, diminished, virtual
Conclusion Convex Mirror
The distance object, u
Characteristics of image
u < f Diminished In Size, Upright, Virtual
f < u < 2f Diminished In Size, Upright, Virtual
u > 2f Diminished In Size, Upright, Virtual
Conclusion Diminished In Size, Upright, Virtual
Application reflection of light use in plane mirror
1) A rear view mirror and a side mirror of a car in order to enable the driver see objects at the back and side of the car.
Side mirror Of Car
Application reflection of light
2) A mirror periscope can be built by mounting two plane mirrors in a cardboard tube.
Application reflection of light
3)Plane mirror acts as an anti-parallax error mirror in electrical instruments such as the voltmeter and the ammeter.
Application Of Concave mirror
(1) A shaving mirror or a make-up mirror
used a wide-aperture concave mirror with a large radius of curvature.
(2) A torchlight or a headlight of motor vehicles used concave
parabolic mirror to produce a beam of parallel light rays.
ONOFF
Car head lampCurved mirror
lamp
LOW BEAM
HIGH BEAM
Motor vehicles used concave parabolic mirror for high beam and low beam
Sometimes motor vehicles used difference of filament to produce high and low beam
3) Convex mirror are mounted at a sharp corner of a road so that the drivers are able to see oncoming cars on the blind side of the corner.
Convex mirror4)Convex mirror hung on the corner of
ceilings in supermarkets serve to provide a wide field of view activities happening in the shopping area.