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Physics Lecture 14

# Physics Lecture 14 - Lecture 14 Waves Particles 1800s light...

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Lecture 14: Waves & Particles 1800s light is a wave Maxwell light is an EM wave I. Photoelectric Effect a. classically – if you increase A (increase I) you see a increase in frequency of electrons b. experimentally this was not true c. If f < f t no electrons ejected, regardless of I d. If f > f t electrons are ejected, number per second grows with intensity, max kinetic energy grows with frequency e. 1905 Einstein light is composed of particles photons Energy of Photons: E ph = hf f. To eject electrons: need E ph > E binding where E binding is the work function E ph > φ electrons are ejected i. Threshhold: E ph = φ hf t = φ f t = φ/h g. K max leftover energy if f > f t K max E ph – φ = hf – φ h. Intensity = power/area Power = energy/time i. Intensity number of photons per second per meter squared 1. Frequency  Energy 2. Intensity  Number per second i. Concept test – Power = 5 for two lasers. One wavelength is 633nm and the other is 840 nm. Which laser emits more photons?

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