Historical development of light theory
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  • 1. Historical MilestonesDevelopment of Light Theory
  • 2. Historical Development Isaac Newton – Particle Theory & Prism Christiaan Huygens – Wave Theory Thomas Young – Double-Slit Experiment James Maxwell – Electromagnetic Theory Heinrich Hertz – Radiowaves & Wireless Experiment William Roentgen – X-rays Max Planck – Radiation Theory Albert Einstein – Photo Model
  • 3. Isaac Newton (1642-1727)  Particle Model of Light (1671)  Light rays is comprised of a stream of massless particles
  • 4. 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
  • 5. 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
  • 6. 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
  • 7. 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
  • 8. 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
  • 9. A coherent light is shone through a thin plate pierced by two parallel slitshttp://www.thestargarden.co.uk/images/163.%20Double%20slit%20waves.png
  • 10. 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
  • 11. 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.
  • 12. 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
  • 13. Hertz Wireless Experiment (1887) http://www.sparkmuseum.com/HERTZ.HTM
  • 14. 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
  • 15. William Konrad Roentgen (1845-1923)  Produced and detected x-rays  Nobel Prize in Physics (1901)
  • 16. 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
  • 17. 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