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Quantum Theory Final

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• Quantum Theory Final

1. 1. quantum theory NJF
2. 2. Introduction <ul><li>This is a two lesson presentation. </li></ul><ul><li>It is designed to help you understand the true weirdness of nature, i.e.quantum theory. </li></ul><ul><li>Don’t get too comfy – you are going to do some work. </li></ul><ul><li>Concentrate and ask questions. </li></ul>
3. 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. 4. Particle nature of light <ul><li>Slow exposure of a photograph </li></ul>
5. 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. 6. <ul><li>“ It does not do harm to the mystery to know a little about it. </li></ul><ul><li>Far more marvellous is the truth than any artists of the past imagined! ” </li></ul><ul><li>- Richard Feynman </li></ul>It takes a little genius
7. 7. Who was Richard Feynman? <ul><li>“ Richard Feynman was to the second half of the 20 th century what Einstein was to the first: the perfect example of scientific genius” </li></ul><ul><li>Frank McLynn, Independent. </li></ul>
8. 8. A new way of seeing
9. 9. The truth about light <ul><li>It comes in packets called photons. </li></ul><ul><li>They each have an energy E=hf </li></ul><ul><li>Dim blue light contains identical photons to bright blue light – just less of them. </li></ul><ul><li>We can never know the route a photon will take we can only calculate probabilities. </li></ul><ul><li>QUANTUM THEORY RECONCILES THESE FACTS WITH THE OBSERVED WAVE LIKE BEHAVIOUR OF LIGHT e.g. INTERFERENCE, DIFFRACTION …. </li></ul>
10. 10. <ul><li>Real reflection </li></ul>
11. 11. Introduction <ul><li>All paths method – look at </li></ul><ul><li>text book page 163 </li></ul>
12. 12. QUANTUM MODEL OF REFLECTION
13. 14. <ul><li>Ask: In what ways can we…? </li></ul><ul><ul><li>Assess the situation. Get the facts. </li></ul></ul><ul><ul><li>Generate possible solutions with green light, non-judgmental thinking. </li></ul></ul><ul><ul><li>Select the best solution. </li></ul></ul>
14. 15. Results table EXERCISE 1
15. 16. method
16. 18. Adding arrows. Finding probability.
17. 19. TESTING THE THEORY
18. 21. QUANTUM MODEL OF REFRACTION
19. 22. EXERCISE 2 Homework ‘ try all paths refraction’
20. 23. EXAMPLE OF PATH OF LEAST TIME
21. 24. QUANTUM MODEL OF DIFFRACTION
22. 26. QUANTUM MODEL OF LENSES – TRICKING PHOTONS
23. 28. SUMMARY <ul><li>Photons show quantum behaviour. </li></ul><ul><li>Quantum behaviour is unique – neither wave nor particle behaviour. </li></ul><ul><li>Quantum behaviour combines phasors from all possible paths. </li></ul><ul><li>The probability of an event is got from the square of the resultant phasor amplitude. </li></ul>
24. 29. <ul><li>I can show my understanding of effects, ideas and relationships by describing and explaining: </li></ul><ul><li>how phasor arrows come to line up for paths near the path that takes the least time </li></ul><ul><li>how phasor arrows 'lining up' and 'curling up' accounts for reflection, propagation, refraction, focusing, diffraction and interference </li></ul><ul><li>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 </li></ul><ul><li>evidence for random arrival of photons </li></ul><ul><li>I can interpret: </li></ul><ul><li>diagrams illustrating how paths contribute to an amplitude </li></ul>LEARNING OUTCOMES
25. 30. Recommended Reading <ul><li>QED the strange theory of light and matter. </li></ul><ul><li>Six Easy Pieces </li></ul>