1. 27.1 – EARLY CONCEPTS OF LIGHT
Particle
Wave
Newton
Move in straight line
Massless bundles of light energy – photon
Einstein – 1905
Light has dual nature
Huygens
Spread out
Wave theory accepted in 19th century

2. 27.2 – Speed of Light So fast – very difficult to measure Roemer
Measured the orbital period of Jupiter’s moon, Io using a telescope
When earth is further away in its orbit, light takes longer

3. Huygens
Reflects off octagonal mirror
Figured out light traveled extra distance
Spinning at correct rate = light seen through eyepiece
Give value ~ km/s
Nobel prize 1907 – first American
Michelson
Light reflected to and from distance source

4. 27.3 – Electromagnetic Waves
Due to accelerating electric charges
Travels as alternating electric & magnetic field
Part of a EM spectrum

5. 27.4 – Light & Transparent Materials
Transmitting of light
Atoms absorb & immediately reemit because of vibrating electrons
Materials have particular “natural vibrating frequency”
Depends on attraction of e to nucleus
Ultraviolet waves ~ natural frequency (glass) are not transparent

6. Energy held for “some time” causing heating
Visible light – holds energy for less time
Then, pass energy on (as light)
This takes time  light travels slower through transparent materials
Infrared – causes whole atom to resonate  not transparent

7. 27.5 – Opaque Materials Do not allow light through
Energy of light turned into internal energy  making them warmer
Metals have many free e not bound to nucleus
Light causes vibrations of e, but reemitted back out as reflection  why shiny
Atmosphere – trans to visible & some infrared
opaque to ultraviolet (mostly)