Chapter 1 : Chapter 1 :

INTRODUCTION INTRODUCTION TO OPTICSTO OPTICS

OpticsOptics is the physical science which is the physical science which studies light and the laws of vision.studies light and the laws of vision.

Some sources of light …Some sources of light …

1. Light phenomena1. Light phenomena

1.1. Natural and artificial light sources1.1. Natural and artificial light sources

IncandescenceIncandescence FluorescenceFluorescence PhosphorescencePhosphorescence

the sun, a fire, the sun, a fire, the metal wire the metal wire

filament of a filament of a conventional light conventional light

bulbbulb

Fluorescent tubeFluorescent tube the hands of a watch, the hands of a watch, the northern lightsthe northern lights

warm lightwarm light cold lightcold light cold lightcold light

Stops when the Stops when the stimulation stopsstimulation stops

Stops when the Stops when the stimulation stopsstimulation stops

Persists after the Persists after the stimulation stopsstimulation stops

1.2 Illuminated bodies.1.2 Illuminated bodies.

Opaque bodiesOpaque bodies allow no light to pass through them allow no light to pass through them

Translucent bodies:Translucent bodies: some light passes through but the some light passes through but the light is scattered and does not allow the shapes of light is scattered and does not allow the shapes of objects to be distinguished.objects to be distinguished.

Transparent bodiesTransparent bodies: light passes through without being : light passes through without being scattered, allowing the shapes of objects to be scattered, allowing the shapes of objects to be distinguished.distinguished.

Translucent versus Translucent versus transparenttransparent

2. WHAT IS LIGHT?2. WHAT IS LIGHT?

Light is part of a large family of waves with Light is part of a large family of waves with similar properties: similar properties: electromagnetic waveselectromagnetic waves..

All electromagnetic waves travel at the same All electromagnetic waves travel at the same speed ‘speed ‘cc’ in a vacuum or in air: ’ in a vacuum or in air:

c = 300 000 km/sc = 300 000 km/s

In other media (water, glass, diamond…), In other media (water, glass, diamond…), the speed of light, denoted the speed of light, denoted vvmediummedium , is less , is less than than cc

vvmediummedium < < cc

vvwaterwater = 225 000 km/s= 225 000 km/s vvglassglass = 200 000 km/s= 200 000 km/s vvdiamonddiamond = 120 000 km/s= 120 000 km/s

Rather than giving the value of vRather than giving the value of vmedium medium

, we prefer to give the , we prefer to give the refractive refractive indexindex of the medium, denoted n of the medium, denoted nmedium medium

and defined by:and defined by:cc

vvmediummedium

nnmediummedium = =

Calculate the refractive indices of Calculate the refractive indices of water, glass and diamond.water, glass and diamond.

nnwater water = 1.33= 1.33 nnglass glass = 1.5= 1.5 nndiamond diamond = 2.5= 2.5

3. The hypothesis of geometrical 3. The hypothesis of geometrical opticsoptics

3.1. Experiment3.1. Experiment Experimental setupExperimental setup

Conclusion : in a homogenous Conclusion : in a homogenous transparent medium, transparent medium, light travels in light travels in a straight linea straight line..

homogenoushomogenous : having the same properties : having the same properties throughoutthroughout

3.2. Schematic representation3.2. Schematic representation We represent the path of the light by We represent the path of the light by

a straight line called the a straight line called the light raylight ray. . The arrow indicates the direction of The arrow indicates the direction of travel of the light.travel of the light.

Light from a point source spreads in Light from a point source spreads in all directions.all directions.

A A light beamlight beam is a collection of light rays. is a collection of light rays.

4. Applications4. Applications

4.1. 4.1. The pinhole cameraThe pinhole camera Experimental setupExperimental setup

A'A'

B'B'

C'C'

Interpretation : the formation of the Interpretation : the formation of the inverted image is explained by the inverted image is explained by the straight line (rectilinear) propagation straight line (rectilinear) propagation of light.of light.

4.2. 4.2. ShadowsShadows object illuminated by a point source object illuminated by a point source

SSPointPoint

source source Large sphereLarge sphere

SmallSmallspheresphere

screenscreen

object illuminated by an extended sourceobject illuminated by an extended source

screenscreen

SSExtendedExtendedsource source

spheresphere

Eclipse of the moon (lunar eclipse)Eclipse of the moon (lunar eclipse)

sunsunEarthEarth

MoonMoon

Eclipse of the sun (solar eclipse)Eclipse of the sun (solar eclipse)

sunsun

EarthEarth

MoonMoon

Electromagnetic wavesElectromagnetic waves

visible spectrumvisible spectrum

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