1. LIGHT

2. Early Concepts Light first thought to consist of particles Socrates, Plato, and Euclid Later thought and proved that Empedocles and Huygens Einstein Light consists of – massless bundles of aka

3. Speed of Light Light travel instantaneously or w/finite speed? Galileo tried to measure time light takes to travel back and forth using

4. measured periods of Jupiter’s moons – esp. Io b/c Io behind Jupiter, its should be predictable found in observed period while earth moving away from Jupiter, while earth moving toward Jupiter,

5. Huygens interpreted Roemer’s observations Speed of Light Determined by

6. Michelson directed by lens to octagonal mirror at rest Mirror carefully adjusted so beam of on mountain 35 km away Light back to octagonal mirror and into eye of observer Only had to measure for light to make Experimental value for speed of light = speed of light rounded to

7. Light travels fast Light-year –

8. Calculating w/ Speed of Light d = c = d = t = will need to use dimensional analysis See p408 Computational Example for review

9. Electromagnetic Waves Light is energy emitted by Energy that travels in a wave that Electromagnetic Spectrum (p408 Fig 27.4) Range of radio waves, microwaves, infrared, light, UV, xrays, gamma rays