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  1. 1. 1Nature of Lightas Waves
  2. 2. 2What is Light?•The natural agent thatstimulates sight and makesthings visible.•Electromagnetic radiationfrom about 390 to 740 nm inwavelength.
  3. 3. "Is light a waveor a stream ofparticles?"3
  4. 4. 4Let’s first analyzecharacteristicsbehaviors of light as awave.
  5. 5. Reflection• All waves are known toundergo reflection or thebouncing off of an obstacle.5
  6. 6. Refraction• Change in direction of propagation ofany wave as a result of its traveling atdifferent speeds at different pointsalong the wave front.• All waves are known to undergorefraction when they pass from onemedium to another medium.6
  7. 7. Diffraction• Diffraction involves a change indirection of waves as they passthrough an opening or around anobstacle in their path.7
  8. 8. Interference8• In 1807, Thomas Young(1773-1829) did themost convincingexperimentdemonstrating that lightis a wave.• A beam of light fell on apair of parallel, verythin slits in a piece ofmetal.• After passing throughthe slits, the light fellon a screen.• A pattern of alternatingbright and dark bandsformed is called aninterference pattern.
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  10. 10. Interference• Wave interference is a phenomenonthat occurs when two waves meetwhile traveling along the samemedium.10
  11. 11. Polarization• Polarized light waves are light wavesin which the vibrations occur in asingle plane. The process oftransforming un-polarized light intopolarized light is known aspolarization.11
  12. 12. Polarization• The fact that light shows polarizationtells us that light is a transversewave.• Transverse waves are waves thatcause the particles of the medium tovibrate perpendicularly to thedirection of motion.12
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  14. 14. 14Polarization Hint• Light vibrates in all directions.• A polarizing filter acts like a picketfence. It only lets certain directionvibrations pass through it.• Therefore, if you pass light throughtwo of them you can completelyblock the light from passing through.• HOW?
  15. 15. 15Polarization
  16. 16. 16Now what about theparticle-like behavior?
  17. 17. 17The photoelectric effect is observedwhen light of a certain frequencystrikes a metal and ejects electrons.
  18. 18. 18PhenomenonCan be explained in terms ofwaves.Can be explained interms of particles.Reflection                              Refraction                              Interference                              Diffraction                              Polarization                              Photoelectriceffect                            
  19. 19. 19What is Light?
  20. 20. 20• Light is a special type of wave.• What we know as light or VISIBLELIGHT is actually a type of somethingcalled ELECTROMAGNETIC RADIATION.• So, what is electromagnetic radiationand electromagnetic waves?
  21. 21. 21Electromagnetic Radiation• When something creates energy it alsoemits radiation. Depending on theamount of energy, the object will emitdifferent types of electromagneticradiation.• When we studied mechanical waves,they were all transferred through amedium. What medium is lighttransferred through?
  23. 23. 23Electromagnetic Waves• Electromagnetic waves are wavesthat do not need a medium topropagate through.• But what is creating thedisturbance? What is emittingthis energy?
  24. 24. ELECTRONS24
  25. 25. 25Electromagnetic Waves• Electromagnetic waves areeverywhere.• Light is only a small part of them– Radios– TVs– Microwaves– Light (Visible/UV/InfraRed)– Radiation– Lasers– CD/DVDplayers– X-Rays
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  27. 27. 27Electromagnetic Waves• Electrons in materials are vibrated andemit energy in the form of photons,which propagate across the universe.• Photons have no mass, but are pureenergy.• Electromagnetic Waves are waves thatare made up of these “photons”.
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  29. 29. The Corpuscular Theory• Created in the seventeenth centuryby Sir Isaac Newton • States that light emitted by luminousobjects consist of tiny particles ofmatter called corpuscles. Whencorpuscles hit a surface, each particleis reflected. • Thought that light traveling from airinto water will increase the speed,while light entering water willdecrease the speed.29
  30. 30. The Wave Theory• Discovered by Christian Huygens, a Dutch scientist,also in the seventeenth century • States that light is emitted in a series of waves thatspread out from a light source in all directions. Thesewaves are not affected by gravity. • Furthermore, he disagreed with Newton and said thatlight traveling from air to water will decrease thespeed, and vice versa. Huygens was proved later tobe correct. • 100 years later, Englishman ThomasYoung completely disproved the corpuscular theoryby showing that light waves can interfere with eachother. 30
  31. 31. The Electromagnetic Theory• Discovered in the nineteenth centuryby James Maxwell • Proposed that light waves do not requirea medium for transmission. • Light waves posses electrical andmagnetic properties and can travelthough a vacuum. Light waves are a partof a larger family of electromagneticwaves and make up the electromagneticspectrum.31
  32. 32. The Quantum Theory• Discovered by Max Planck, Germanscientist in 1900 • Stated that light waves travel asseparate packets of energycalled quanta or photons.• Merged the subjects of theCorpuscular, Wave, andElectromagnetic Theories together.• Later, it was proved that the correctand most accurate theory was theQuantum Theory.32
  33. 33. • Quantum Theory explains thatlight has both properties ofwaves and particles thus,light is both waveand particle.33
  34. 34. Both particles and waves?!?What the hell?!© 2003 Mike Maloney 34
  35. 35. © 2003 Mike Maloney 35
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  37. 37. Yes! Malapitnarecess!!!© 2003 Mike Maloney 37