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Nature of Light● And God said, Let there be light: and there was
light. And God saw the light, that it was good: and God divided the light from the darkness. - Genesis 1:3-4
● And God said, This is the token of the covenant which I make between me and you and every living creature that is with you, for perpetual generations: I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth. - Genesis 9:12-13
Rainbow Bridge
What is light?
Early Observations● Empedocles (500 BC)
– Light has motion and travels at a fixed speed
● Aristotle (332 BC)– Pure light changed into colors by contamination
● Egyptians (200 AD)– Light travelels from eye to illuminate object
● Alhazen (965 AD)– Light comes from sun or other objects
– Made curved mirrors and pinhole camera obscura
Early Observations● Leonardo da Vinci
– Studied the ''Artificial Rainbow'' obtained by passing pure light through a prism
● Galileo (1600)– Tried to measure speed of light
Early Observations● Newton
– Studied chromatic aberration in lenses
– Studied light passing through prisms● Selected the brightest seven: Red, Orange, Yellow,
Green, Blue, Indigo, and Violet● These are arbitrary
– Thought light was comprised of corpuscles● Unable to completely explain color
– Nature and Nature's Law lay hid at night.God said, 'Let Newton be,' and all was light.
Early Observations● Christian Huygens
– Published the wave theory of light in 1690
– Could easily explain refraction
– Hard to explain light travelling in a vacuum● Light carried on ''ether''
● Thomas Young (1801)– Double slit experiment
– Determined wavelength of red light of 750 nm
● Augustin Jean Fresnel (1816)– Created diffraction gratings
Electromagnetic Radiation● Sir William Herschel (1799)
– Using a prism and a thermometer discovered infrared radiation
– Showed it behaves like visible light
● Johann Wilhelm Ritter– Used silver chloride to detect ultraviolet light
● James Clerk Maxwell (1864)– Theorized radiation beyond infrared
– Produced and identified in 1887 by Heinrich Hertz
Dual Nature of Light● Max Planck
– Radiation has a wave form
– Made of small units of energy, called a quanta
– Unified earlier theories
● On Monday, Wednesday, and FridayWaves boasted, ''It's my day,''On Tuesdays, Thursdays, and SaturdayParticles sang, ''Due it my way.''Sundays, though, were the very bestThe good Lord said, ''It's a day of rest.''
Electromagnetic Radiation
X-Rays● Wilhelm Konrad Roentgen (1895)
Roentgen Rays● The Roentgen Rays, the Roentgen Rays
What is this craze:The town's ablazeWith the new phraseOf x-rays' ways.I'm full of daze,Shock and amazeFor nowadaysI hear they'll gazeThro' cloak and gown – and even stays,Those naughty, naughty Roentgen Rays.
Roentgen Rays● We do not want, like Dr. Swift,
To take off our flesh and pose inOur bones, or show each little riftAnd joint fro you to poke your nose in.
- London's Punch magazine, 1896
Polarization
Interference
Diffraction
Reflection
Refraction
Total Internal Reflection
Prisms and Lenses● Early lens dicovered in ruins of Nineveh
believed to be 4000 years old
Concave lenses
Convex lenses
Speed of Light● Galileo
– Used lanterns separated by increasing distances
– No valuable estimate
● Olaus Roemer (1675)– Used eclipses of Jupiter's satellites
– Obtained a speed of 140,000 miles per second
– Riduculed by the French Academy of Sciences:''It is absolutely impossible for anything, unless by the spirit of God, to attain such a a speed''
Speed of Light● Jean Bernard Leon Focault (1850)
– Used a rotaing mirror system
– Obtained a speed of 187,000 miles/sec
● Albert Abraham Michelson (1879)– Obtained a speed of 186,284 miles/sec
● Current Speed is 186,284 miles/sec