Development of Light Theory

Historical Milestones

Historical Development

Isaac Newton – Particle Theory & PrismChristiaan Huygens – Wave TheoryThomas Young – Double-Slit Experiment James Maxwell – Electromagnetic TheoryHeinrich Hertz – Radiowaves & Wireless

ExperimentWilliam Roentgen – X-raysMax Planck – Radiation TheoryAlbert Einstein – Photo Model

Isaac Newton (1642-1727)

Particle Model of Light (1671)

Light rays is comprised of a stream of massless particles

Particle Model of Light (1671)

Explains straight-line propagation of light: Follows laws of reflection and refraction

Explains colours of light: White light contains different colour particles Prism sorts the different particles of light

http://www.sciencephoto.com/image/227396/530wm/H4140126-Newton_s_optics-SPL.jpg

Christiaan Huygens (1629-1695)

Wave Theory (1678)

Light is a wave that can transfer energy without transferring matter

Light waves have varying wavelengths, frequencies, speeds and amplitude

Wave Theory (1678)

Follows laws of reflection and refraction Explains diffraction: the effect of waves

when encountering an obstacle Constructive and destructive interference

http://www.sciencephoto.com/image/2511/530wm/A1800254-Water_waves-SPL.jpg

Wave Theory Waves are additive:

constructive interference Example: waves in the ocean

are bigger when more than one wave moves together

Waves are subtractive: destructive interference A wave that meets a trough

of equal amplitude cancel each other out (net zero amplitude)

http://upload.wikimedia.org/wikipedia/commons/3/33/Doubleslit3Dspectrum.gif http://en.wikipedia.org/wiki/File:Doubleslit.svg

Thomas Young (1773 – 1829)

Wave Theory of Light Proved that light

propagates as a wave Performed an

experiment that demonstrated interference patterns in light that followed the rules of diffraction seen in water waves

http://www.thestargarden.co.uk/images/163.%20Double%20slit%20waves.png

A coherent light is shone through a thin plate pierced by two parallel slits

Double-Slit Experiment (1801) wave nature of light causes the light waves

passing through the two slits to interfere, producing bright and dark bands on the screen

James Maxwell (1831–1879)

Electromagnetic Theory Proposed that electric

and magnetic fields travel through space in the form of waves at the speed of light.

Electricity, magnetism and light all manifest together in the form of an electromagnetic field that does not require a medium for transmission.

Heinrich Hertz (1857-1894)

Discovered radio waves

First to prove the existence of electromagnetic waves by using a device that transmit and receive radio pulses

Hertz Wireless Experiment (1887)

http://www.sparkmuseum.com/HERTZ.HTM

Hertz Wireless Experiment (1887)

Engineered a device that makes a spark

If the spark sent EM waves, it would be transmitted and picked up by the receiver which would also spark

Also measured length and velocity of EM wave

Showed that EM wave reflected and refracted the same as light waves

Proved that light is electromagnetic radiation

William Konrad Roentgen (1845-1923)

Produced and detected x-rays

Nobel Prize in Physics (1901)

Max Planck (1858-1947) Radiation theory:

electromagnetic radiation is emitted in quanta

Light energy is not continuous like in a wave

Rather light is delivered in small parcels / packets of energy

Albert Einstein (1879-1955)

Photon model Light functions both

as particle and wave Light is composed of

particles (photons) that travel as waves

Each photon has energy that is proportional to the frequency of its wave