Chapter 1 : INTRODUCTION TO OPTICS

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

Some sources of light …

1. Light phenomena 1.1. Natural and artificial light sources IncandescenceFluorescencePhosphorescence the sun, a fire, the metal wire filament of a conventional light bulb Fluorescent tube the hands of a watch, the northern lights warm light cold light Stops when the stimulation stops Persists after the stimulation stops

1.2 Illuminated bodies. Opaque bodies allow no light to pass through them Translucent bodies: some light passes through but the light is scattered and does not allow the shapes of objects to be distinguished. Transparent bodies: light passes through without being scattered, allowing the shapes of objects to be distinguished.

Translucent versus transparent

2. WHAT IS LIGHT? Light is part of a large family of waves with similar properties: e e e e e llll eeee cccc tttt rrrr oooo mmmm aaaa gggg nnnn eeee tttt iiii cccc w w w w aaaa vvvv eeee ssss. All electromagnetic waves travel at the same speed ‘c’ in a vacuum or in air: c = km/s

In other media (water, glass, diamond…), the speed of light, denoted vmedium, is less than c vmedium < c vwater = km/s vglass = km/s vdiamond = km/s

Rather than giving the value of vmedium, we prefer to give the refractive index of the medium, denoted nmedium and defined by:c v medium n medium =

Calculate the refractive indices of water, glass and diamond. nwater = 1.33 nglass = 1.5 ndiamond = 2.5

3. The hypothesis of geometrical optics 3.1. Experiment Experimental setup

Conclusion : in a homogenous transparent medium, light travels in a straight line. homogenous : having the same properties throughout

3.2. Schematic representation We represent the path of the light by a straight line called the light ray. The arrow indicates the direction of travel of the light. Light from a point source spreads in all directions.

A light beam is a collection of light rays.

4. Applications 4.1. The pinhole camera Experimental setup A' B' C'

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

4.2. Shadows object illuminated by a point source S Point source Large sphere Small sphere screen

object illuminated by an extended source screen S Extended source sphere

Eclipse of the moon (lunar eclipse) sun Earth Moon

Eclipse of the sun (solar eclipse) sun Earth Moon

Electromagnetic waves visible spectrum BACK