Early Concepts of Light (Wrong!!) Ancient Greece –Some believed light consisted of particles that entered the eye to produce sight –Plato & Socrates believed that eyes emitted “streamers” making contact with objects, allowing sight

Who got it right? Greek Philosopher/Scientist, Empedocles, was the first to teach that light traveled in waves –Wave Theory was accepted by nineteenth century

Instantaneous or Finite Speed? Danish Astronomer, Olaus Roemer was the first to demonstrate that light traveled with a finite speed!!!

How Fast? American Physicist, Albert Michelson (1880) Winner of the 1907 Nobel Prize Determined speed to be 299,920 km/s

Light Light & Electromagnetic Waves

Light Fundamentals Light - An Example of a Transverse Wave Speed of Light 3.0x 10 8 m/sSpeed of Light 3.0x 10 8 m/s

Light Fundamentals Light is electromagnetic radiation Light is simply a form of Energy that travels as a transverse wave. All electromagnetic waves travel at 3.0 x 10 8 m/s More on the Electromagnetic SpectrumElectromagnetic Spectrum

Light Sources –luminous vs. illuminous emits light vs. reflects light

Light Fundamentals Inverse-Square Relationship –The illuminance of a body varies inversely with the square of the distance from the light source Luminous Flux, P –rate at which light is emitted (measured in lumens, lm) Luminous Intensity –the luminous flux that falls on one square meter

Light Fundamentals Illuminance, E –The illuminous Intensity of a surface Measured in lumens per square meter or a lux, lx) E = P / 4  r 2

Light and Matter Transparent Materials –Materials that allow light to pass through them in straight lines.

Light and Matter Translucent Materials –Materials that transmit light but do not allow objects to be seen clearly through them.

Light and Matter Opaque Materials –Materials that absorb or reflect light without remission and therefore allow NO light to pass through them. –Opaque materials often create shadows where light can not reach

Light and Matter Polarization of Light –The aligning of vibrations in a transverse wave, usually by filtering out waves of other directions –3D movies… and other tricks… Demos