Chapter 27 - Light
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Transcript Chapter 27 - Light
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)