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27.1 – EARLY CONCEPTS OF LIGHT

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 19 th century. 27.2 – Speed of Light. So fast – very difficult to measure Roemer

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27.1 – EARLY CONCEPTS OF LIGHT

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  1. 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

  2. 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

  3. 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

  4. 27.3 – Electromagnetic Waves • Due to accelerating electric charges • Travels as alternating electric & magnetic field • Part of a EM spectrum

  5. 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

  6. 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

  7. 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)

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