4Let’s first analyzecharacteristicsbehaviors of light as awave.
Reflection• All waves are known toundergo reflection or thebouncing off of an obstacle.5
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
Diffraction• Diffraction involves a change indirection of waves as they passthrough an opening or around anobstacle in their path.7
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.
Interference• Wave interference is a phenomenonthat occurs when two waves meetwhile traveling along the samemedium.10
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
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
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?
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?
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?
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”.
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
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
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
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
• Quantum Theory explains thatlight has both properties ofwaves and particles thus,light is both waveand particle.33