Light Electromagnetic Waves Early Concepts of Light Wrong

Light & Electromagnetic Waves

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 Fundamentals • Light - An Example of a Transverse Wave Speed of Light 3. 0 x 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

Michelson-Morely Experiment • Is the speed of light always the same? • YEP

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 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 – 3 D movies… and other tricks… Demos