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HSC Physics

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  1. Module 1: Kinematics
    1.1 Motion in a Straight Line
  2. 1.2 Motion on a Plane
  3. Module 2: Dynamics
    2.1 Forces
  4. 2.2 Forces, Acceleration and Energy
  5. 2.3 Momentum, Energy and Simple Systems
  6. Module 3: Waves and Thermodynamics
    3.1 Wave Properties
  7. 3.2 Wave Behaviour
  8. 3.3 Sound Waves
  9. 3.4 Ray Model of Light
  10. 3.5 Thermodynamics
  11. Module 4: Electricity and Magnetism
    4.1 Electrostatics
  12. 4.2 Electric Circuits
  13. 4.3 Magnetism
  14. Module 5: Advanced Mechanics
    5.1 Projectile Motion
  15. 5.2 Circular Motion
  16. 5.3 Motion in Gravitational Fields
    2 Topics
  17. Module 6: Electromagnetism
    6.1 Charged Particles, Conductors and Electric and Magnetic Fields
  18. 6.2 The Motor Effect
    1 Topic
  19. 6.3 Electromagnetic Induction
  20. 6.4 Applications of the Motor Effect
    1 Topic
  21. Module 7: The Nature of Light
    7.1 Electromagnetic Spectrum
    3 Topics
  22. 7.2 Light: Wave Model
  23. 7.3 Light: Quantum Model
    2 Topics
  24. 7.4 Light and Special Relativity
  25. Module 8: From the Universe to the Atom
    8.1 Origins of the Elements
    5 Topics
  26. 8.2 Structure of the Atom
    3 Topics
  27. 8.3 Quantum Mechanical Nature of the Atom
    2 Topics
  28. 8.4 Properties of the Nucleus
    2 Topics
  29. 8.5 Deep Inside the Atom
    4 Topics
Lesson 21, Topic 2
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Measuring the Speed of Light

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1368 Galileo

  • Galileo turns on lantern, starts clock
  • Assistant sees light, turns on own lantern
  • Galileo sees other lantern, he stops clock

Results

  • No perceptible lag
  • > 10x the speed of sound
  • “if not instantaneous, it [light] is extraordinarily rapid”

1685 Ole Roemer

Measured c by observing Io, one of Jupiter’s moons

  • When Earth was close to Io, orbital T = 42.5 h
  • When further away, T was larger
  • Dividing the change in distance by the change in observed period gave Roemer’s calculation of the speed of light.

Results

  • Roemer approximated c = 2.14 \times 10^8 \text{ms}^{-1}

1677 Christiaan Huygens

Updated Roemer’s estimate with better estimates of distances to Io.

Results

  • Huygnens approximated c = 2.01168 \times 10^8 \text{ms}^{-1}