Quantum Theory
- 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 to comfy – you are going too 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 take 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 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 ….
- 12. QUANTUM MODEL OF REFLECTION
- 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
- 18. Adding arrows. Finding probability.
- 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
- 26. QUANTUM MODEL OF LENSES – TRICKING PHOTONS
- 30. Recommended Reading QED the strange theory of light and matter. Six Easy Pieces