27.1 – EARLY CONCEPTS OF LIGHT
Particle
Newton
 Move in straight line
 Massless bundles of
light energy – photon
 Einstein – 1905
 Light has dual nature
Wave
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

 Figured out light traveled
extra distance

 Give value ~ 300000
km/s

Michelson
 Light reflected to and
from distance source
Reflects off octagonal
mirror
Spinning at correct rate
= light seen through
eyepiece
Nobel prize 1907 – first
American
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)