Transcript Light Fundamentals

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?
1675 - 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
&
Electromagnetic Waves
Light Fundamentals
• Light - An Example of a Transverse Wave
• Speed of Light 3.0x 108 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
108 m/s
• More on the Electromagnetic Spectrum
Light Sources
• 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r2
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