27.1 – EARLY CONCEPTS OF LIGHTParticle WaveNewtonMove in straight

lineMassless bundles

of light energy – photon

Einstein – 1905

Light has dual nature

HuygensSpread outWave theory

accepted in 19th century

27.2 – Speed of LightSo fast – very difficult

to measureRoemerMeasured the orbital

period of Jupiter’s moon, Io using a telescope

When earth is further away in its orbit, light takes longer

HuygensFigured out light

traveled extra distance

Give value ~ 300000 km/s

MichelsonLight reflected to and

from distance sourceReflects off octagonal

mirrorSpinning at correct

rate = light seen through eyepiece

Nobel prize 1907 – first American

27.3 – Electromagnetic WavesDue to accelerating electric chargesTravels as alternating electric & magnetic

fieldPart of a EM spectrum

27.4 – Light & Transparent Materials

Transmitting of lightAtoms 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 timeThen, pass energy on (as light)This takes time light travels slower

through transparent materialsInfrared – causes whole atom to resonate

not transparent

27.5 – Opaque MaterialsDo not allow light throughEnergy of light turned into internal energy

making them warmerMetals have many free e not bound to nucleusLight causes vibrations of e, but reemitted

back out as reflection why shinyAtmosphere – trans to visible & some infrared

opaque to ultraviolet (mostly)