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Quantum Theory Final

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  • Transcript

    • 1. quantum theory NJF
    • 2. 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 to do some work.
      • Concentrate and ask questions.
    • 3. Wave nature of light This image is of a bright light photographed through 'crossed gratings' – two diffraction gratings set perpendicular to one another.
    • 4. Particle nature of light
      • Slow exposure of a photograph
    • 5. 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
    • 6.
      • “ 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
    • 7. 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.
    • 8. A new way of seeing
    • 9. 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 photon will take we can only calculate probabilities.
      • QUANTUM THEORY RECONCILES THESE FACTS WITH THE OBSERVED WAVE LIKE BEHAVIOUR OF LIGHT e.g. INTERFERENCE, DIFFRACTION ….
    • 10.
      • Real reflection
    • 11. Introduction
      • All paths method – look at
      • text book page 163
    • 12. QUANTUM MODEL OF REFLECTION
    • 13.  
    • 14.
      • 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.
    • 15. Results table EXERCISE 1
    • 16. method
    • 17.  
    • 18. Adding arrows. Finding probability.
    • 19. TESTING THE THEORY
    • 20.  
    • 21. QUANTUM MODEL OF REFRACTION
    • 22. EXERCISE 2 Homework ‘ try all paths refraction’
    • 23. EXAMPLE OF PATH OF LEAST TIME
    • 24. QUANTUM MODEL OF DIFFRACTION
    • 25.  
    • 26. QUANTUM MODEL OF LENSES – TRICKING PHOTONS
    • 27.  
    • 28. SUMMARY
      • Photons show quantum behaviour.
      • Quantum behaviour is unique – neither wave nor particle behaviour.
      • Quantum behaviour combines phasors from all possible paths.
      • The probability of an event is got from the square of the resultant phasor amplitude.
    • 29.
      • I can show my understanding of effects, ideas and relationships by describing and explaining:
      • how phasor arrows come to line up for paths near the path that takes the least time
      • how phasor arrows 'lining up' and 'curling up' accounts for reflection, propagation, refraction, focusing, diffraction and interference
      • that the probability of arrival of a photon is determined by graphical addition of arrows representing the phase and the amplitude of the quantum for selected possible paths
      • evidence for random arrival of photons
      • I can interpret:
      • diagrams illustrating how paths contribute to an amplitude
      LEARNING OUTCOMES
    • 30. Recommended Reading
      • QED the strange theory of light and matter.
      • Six Easy Pieces