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