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
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
Huygens Reflects off octagonal mirror Figured out light traveled extra distance Spinning at correct rate = light seen through eyepiece Give value ~ 300000 km/s Nobel prize 1907 – first American Michelson Light reflected to and from distance source
27.3 – Electromagnetic Waves Due to accelerating electric charges Travels as alternating electric & magnetic field Part of a EM spectrum
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
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
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)