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# L02 - LIGHT Electromagnetic Energy Light =c h Planck...

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Dr. P. Lucas U of A MSE 110 LIGHT • Electromagnetic Energy: Light E = h υ υ =c/ λ h: Planck constant h = 6.626x10 -34 J.s Duality wave/particle of the light: two possible descriptions

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Dr. P. Lucas U of A MSE 110 DUALITY WAVE/PARTICLE OF LIGHT • Ligth as a wave : Electromagnetic wave : Electric and Magnetic field oscillating All the characteristics of a wave : • wavelength • amplitude • phase (time dependence) • velocity: c
Dr. P. Lucas U of A MSE 110 Ligth as a particle : photons DUALITY WAVE/PARTICLE OF LIGHT • Photons have no mass but : • Have momentum p=h/ λ • Can transfer energy through collisions • Carry quantized amount of energy (energy packet) E=h υ

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Dr. P. Lucas U of A MSE 110 QUANTIZATION OF ENERGY Quantization of energy : energy can only be transferred in packets. Max Planck ’s idea. • He developed the mathematical formalism (1900). • But never truly believed in it. It was Einstein who demonstrated quantization 5 years later with the photoelectric effect. • He demonstrated the particle nature of light: photon. • It was the first step towards the development of quantum physics which describes the nature of atoms.
Dr. P. Lucas U of A MSE 110 Einstein’s photoelectric effect QUANTIZATION OF ENERGY • The current is proportional to the intensity of the light h ν 1 h ν • Na cathode hit by light of energy E=h υ . Na • Cathode and anode in vacuum tube. Cathode -, anode + - + • Electrons are attracted by the positively charged anode and cause current to flow.

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L02 - LIGHT Electromagnetic Energy Light =c h Planck...

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