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.