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 Friday Waves boasted, ''It's my day,'' On Tuesdays, Thursdays, and Saturday Particles sang, ''Due it my way.'' Sundays, though, were the very best The 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 ablaze With the new phrase Of x-rays' ways. I'm full of daze, Shock and amaze For nowadays I hear they'll gaze Thro' 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 in Our bones, or show each little rift And 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