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LIGHT

LIGHT. fantastic. Beam Show. Beam Show. University of Southampton. School of Physics and Astronomy. Light: at the forefront of Physics. Light as a wave Relativity Quantum mechanics Particle physics. Light is a Wave.  (wavelength). Evidence. Double slit experiment.

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LIGHT

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  1. LIGHT fantastic

  2. Beam Show Beam Show

  3. University of Southampton School of Physics and Astronomy Light: at the forefront of Physics • Light as a wave • Relativity • Quantum mechanics • Particle physics

  4. Light is a Wave  (wavelength) Evidence Double slit experiment

  5. Double Slit Demo Double Slit Demo

  6. Interference • Constructive(bright points of light) • + + + + + • = Destructive(dark areas) + + + + + =

  7. The DiffractionGrating …colour sorter

  8. Candle Light Candle light

  9. Laser light is coherent, monochromatic and non-dispersive Light Amplification by Stimulated Emission of Radiation Fluorescent Dye: emits a broad spread of wavelengths

  10. Add Dye Add Dye

  11. The Speed of Light For water waves the motion of an observer will “change” the speed of the waves c * c + v * v We should be able to see this effect using the motion of the Earth

  12. Michelson and Morley In 1887 Michelson and Morley did an experiment to detect the aether using the Earth’s motion relative to the aether

  13. Interferometer Demo Interferometer Demo

  14. The experiment failed to detect any time difference for the two paths!

  15. Relativity Light is an electromagnetic wave – there is no aether The speed of light is the same for any observer! This means nothing can travel with light – nothing can reach v=c! Rest mass = energy

  16. Space - Time A flash of light causes a spherical wave front even if you move relative to source This only makes sense if space and time mix! *

  17. Light and Matter Photo-Electric Effect Light can provide energy to kick electrons out of a metal Light e- Metal If light intensity is lowered so there is less energy, we expect the evicted electrons to have less energy… but they don’t… we just see fewer electrons of the same energy… The energy in light comes in lumps!

  18. The size of the energy lumps depends on frequency Light e- Metal If we reduce the frequency too much then the electrons don’t receive enough energy to escape the metal surface

  19. PE Demo PE Demo

  20. Light Quanta The energy in light comes in lumps In a sense we can think of light as particles in our detector - photons Quantum Mechanics is the theory of the dynamics of these quanta

  21. Dirac’s Legacy Electrons can absorb photons e- time But in relativity observers do not agree on time ordering of events… so can we have: e- time

  22. What does it mean for an electron to travel backwards in time? We only measure charge: -q = +q time It looks like a +ve charge electron moving forward in time We have discovered anti-particles!

  23. Particle Physics e- energy in New Particles photon e+ time Electron positron annihilation to a photon allows us to convert their energy to look for all the particles that make up nature

  24. At the LHC collider we produce 100 billion collisions per second! How can we communicate so much data? In 1990 Tim Berners-Lee invented the Web to transfer our data! And laser light now carries the information around the world…

  25. Fibre Optic Fibre Optic

  26. the Lightfantasticwas brought to you by: • Nick Evans • Pearl John • James Gates • Stephen Elsmere • Angela Camerlingo • Mario A. Garcia Ramirez www.lightexpress.soton.ac.uk Thank You For more information, please contact: Pearl John – The Light Express Coordinator: pj@soton.ac.uk 023 8059 2159

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