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Light

  • Can act as a particle or a wave (wave-particle duality)
  • Wavelength
    • λ\lambda
    • Distance between two successive crests
    • Determines colour
  • Frequency
    • ff
    • Herz
    • Cycles per unit of time
  • Speed
    • c  =λfc \; = \lambda f
    • Light travels at 3x108m/s3 x 10^8 m/s
  • Light is additive

Visible Light

Speed of Light

  • 3×105km/s3 \times 10^5 km/s
  • First sign that light's speed was finite came in 1675
    • Ole Rømer observed eclipses of Jupiter's moons
      • Noticed the eclipses happened earlier/later than predicted at opposition/conjunction
      • Since the distance between opposition/conjunction is different, speed of light must be have an impact
  • Takes ~8.3 minutes for light to get from the Sun to Earth
    • 1 AU --> takes light 8 minutes to travel

Physics