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Quantum Theory2
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Quantum Theory2 Quantum Theory2 Presentation Transcript

  • quantum theory NJF
  • Introduction
    • This is a two lesson presentation.
    • It is designed to help you understand the true weirdness of nature, i.e.quantum theory.
    • Don’t get too comfy – you are going too do some work.
    • Concentrate and ask questions.
  • Wave nature of light This image is of a bright light photographed through 'crossed gratings' – two diffraction gratings set perpendicular to one another.
  • Particle nature of light
    • Slow exposure of a photograph
  • Taylors experiment A 0.3 W bulb emits about 0.001 W of visible light at say 6 X 10 14 Hz. Calculate the number of photos emitted each second. E=hf = 4 X 10 -19 J so 2.5 X 10 16 emitted per second At 30cm away, about 1 photon in 5000 enters the eye. Calculate how many photos enter per second and then their average spacing. 2.5 X 10 -19 / 50 000 = 5 X 10 11 this is one every 2 X 10 -12 s. Separation = 2 X 10 -12 X 3 X 10 8 = 6 X 10 -4 m A filter is used to reduce the intensity to 10 -4 of original value, what is the new spacing? Separation increases by 10 4 so now 6 m
    • “ It does not do harm to the mystery to know a little about it.
    • Far more marvellous is the truth than any artists of the past imagined! ”
    • - Richard Feynman
    It takes a little genius
  • Who was Richard Feynman?
    • “ Richard Feynman was to the second half of the 20 th century what Einstein was to the first: the perfect example of scientific genius”
    • Frank McLynn, Independent.
  • A new way of seeing
  • The truth about light
    • It comes in packets called photons.
    • They each have an energy E=hf
    • Dim blue light contains identical photons to bright blue light – just less of them.
    • We can never know the route a photo will take we can only calculate probabilities.
    • QUANTUM THEORY RECONCILES THESE FACTS WITH THE OBSERVED WAVE LIKE BEHAVIOUR OF LIGHT e.g. INTERFERENCE, DIFFRACTION ….
  • Introduction
    • Real reflection
  • Introduction
    • All paths
  • QUANTUM MODEL OF REFLECTION
  •  
    • Ask: In what ways can we…?
      • Assess the situation. Get the facts.
      • Generate possible solutions with green light, non-judgmental thinking.
      • Select the best solution.
  • Results table EXERCISE 1
  • method
  •  
  • Adding arrows. Finding probability.
  • TESTING THE THEORY
  •  
  • QUANTUM MODEL OF REFRACTION
  • EXERCISE 2 Homework ‘ try all paths refraction’
  • EXAMPLE OF PATH OF LEAST TIME
  • QUANTUM MODEL OF DIFFRACTION
  •  
  • QUANTUM MODEL OF LENSES – TRICKING PHOTONS
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  • Recommended Reading
    • QED the strange theory of light and matter.
    • Six Easy Pieces