OpticsTheories

Wave-Particle Duality

Propagation

Wave Speed

Luminosity

Illumination

The Theories of Light

1. Wave Theory• proposed by Christian Huygens in 1690• considers light to be a wave

propagating in ether (an assumed substance permeating all matter and space

2. Corpuscular or Particle Theory• proposed by Isaac Newton in 1704• considers light as composed of tiny

particles emitted by luminous object• cited formation of shadows as proof

The Theories of Light

3. Electromagnetic Theory• proposed by James Clerk Maxwell in

1860• considers light as an electromagnetic

(EM) wave, a transverse wave that is partly electrical and partly magnetic in nature

4. Quantum Theory• proposed by Max Planck in 1900s• considers light as being emitted by

packets of energy called quanta• Einstein called each quantum of

energy as photon

The Dual Nature of Light:A PARTICLE AND A WAVE

• Since light has a dual nature, then it has two models or it can be presented and analyzed in two ways: as a ray and as a wave.

• Ray Model of light is used to describe light as a particle and its behavior as a particle, and such is under the study of GEOMETRIC / RAY OPTICS.

• Wave Model of light is used to describe light as a wave and its behavior as a wave, and such is under the study of WAVE OPTICS.

Measuring the Speed of Light

1. Olaus Roemer – 300 000 000 m/s

2. Christian Huygens – 230 000 000 m/s

3. Armand Louis Fizeau – 313 000 000 m/s

4. Jean Bernard Leon Foucault – 299 796 000 m/s

5. Albert Michelson – 299 799 600 m/s 

Accepted Value:

299 792 458 m/s ~ 300 000 000 m/s

The Rectilinear Propagation of Light

RECTILINEAR PROPAGATION

- property of light to travel in a straight path

- one evidence of rectilinear propagation of light is the creation of a shadow

When can we see objects?

1. Luminous Object – object that can generate its own light

2. Illuminated Object – object that can not generate its own light but can still be seen because it can reflect light that it received from other sources

Types of Luminosity

1. Incandescence – emits light due to their hot bodies.

Types of Luminosity

2. Fluorescence – emits light by utilizing phosphors, which absorbs ultraviolet energy and releases visible light.

Types of Luminosity

3. Phosphorescence – a type of fluorescence where the emission of light persists even after external excitation.

Types of Luminosity

4. Gas Discharge – some gases can be made to produce light by passing an electric current through them.

Types of Luminosity

5. Bioluminescence – light produced in living organisms through chemical reactions between protein and oxygen.

MEASURING LIGHT

Luminous Intensity (I)– strength or brightness of a source of light; measured in candela (cd)

Luminous Flux (F)

– rate at which light is emitted from a source and strikes the surface of a whole sphere; measured in lumens (lm)

Illumination (E)

– the amount of luminous flux falling on a unit area of a surface; measured in lux (lx)

Illumination and Distance:THE INVERSE SQUARE LAW

• Illumination of light is inversely proportional to the square of the distance from the source

• This means that the farther an object is from a light source, the lesser light falls on it.

Examples:• If you move 2× away from a light source, you’ll

receive only 1/4 of the original illuminance.• If you move 3× away from a light source, you’ll

receive only 1/9 of the original illuminance.