# Light

## Light

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##### Presentation Transcript

1. Light What you see (and don’t see) is what you get.

2. Theories of Light • Wave Theory Particle Theory • Huygens Newton • Properties that support each theory Rectilinear Propagation Reflection Refraction Interference Diffraction Photoelectric Effect

3. http://www.electro-optical.com/html/images/em_spect.gif http://www.electro-optical.com/html/images/em_spect.gif

4. http://www.skidmore.edu/~hfoley/images/EM.Spectrum.jpg http://www.skidmore.edu/~hfoley/images/EM.Spectrum.jpg

5. Important Info re EM Spectrum V = f l c = f l c = 3 x 10 8 m/s in vacuum or air l decreases to the right f, E increase to the right E = hf h = 6.63 x 10-34 js 1 angstrom A = 10-10 m 1 nanometer, nm = 10-9 m

6. The Photoelectric Effect Heinrich Hertz first observed this photoelectric effect in 1887. Hertz had observed that, under the right conditions, when light is shined on a metal, electrons are released.

7. In 1905 Albert Einstein provided a daring extension of Planck's quantum hypothesis and was able to explain the photoelectric effect in detail. It was officially for this explanation of the photoelectric effect that Einstein received the Nobel Prize in 1921. The figure below shows a circuit that can be used to analyze the photoelectric effect. Expanding on Planck's quantum idea, Einstein proposed that the energy in the light was not spread uniformly throughout the beam of light. Rather, the energy of the light is contained in "packets" or quanta (the plural of quantum, a single "packet") each with energy of E = h f

8. LASER • Light amplification by stimulated emission of radiation 1. The laser in its non-lasing state

9. 3. Some of these atoms emit photons.